Letter L
_ON ENTOMOLOGICAL INSTRUMENTS; AND THE BEST METHODS OF COLLECTING, BREEDING, AND PRESERVING INSECTS._
Having in my last letter given you some account of the haunts of insects, I now proceed to describe the various instruments with which you ought to be provided, to enable you to collect them; and the best mode of employing each. The Entomologist when he makes an excursion should have three principal objects in view, for which he ought to be duly prepared. The first is to find insects, the next is to catch them, and the last when taken to bring them safe home. In exploring their haunts he must also recollect that some will be reposing; others feeding; others walking or running; others flying; others swimming; others lurking in various places of concealment, and in different states of existence; and that he must be prepared with means of coming at and capturing them under all these circumstances.
1. First furnish yourself with a strong knife or other instrument with which you can raise the bark or penetrate the wood of any tree, when circumstances indicate that insects are busy below the one or within the other. There is no better tool for this and other purposes than Mr. Samouelle's digger, which consists of an iron five inches long, rather more than one-third of an inch in diameter, forming a curve towards the extremity, terminating in a lozenge-shaped point, and strongly fixed in a wooden handle[1554]. With this you may not only explore the interior of timber-trees, but grub up the turf under them, and examine the earth for the pupæ of Lepidoptera. When your object is merely this latter purpose, a potato-fork--which is better than a spade, as it will seldom injure the pupæ--will be your best implement.
2. Next have a stick, to resemble a common walking-stick, sufficiently stout to beat the branches of the trees and shrubs, fitted at one end with a male screw, and at the other with a female, with a brass cap to screw over each to keep the dirt from them. Besides this, you may carry with you a spare piece or two about a foot long, properly equipped to screw to it when you want to lengthen it.
3. Another implement must be a bag-net[1555]. This consists of a hoop of stout brass wire about nine inches or a foot in diameter, with a socket to receive the end of your stick, or, what is more secure, a screw to fix it to it, with a bag of gauze, muslin, or fine canvass, about twelve inches deep, sewed round it. The French collectors use a net of this kind, in which the hoop is formed of two semicircular pieces of iron or brass wire hooked together at one end, and at the other made to lap over the corresponding piece, and pierced to receive the screw at one end of your stick. When not employed, they double the hoop and conceal it under the vest; they fix to it a muslin bag of two feet long. This net is made to serve various purposes. With it they catch Lepidoptera and other flying insects; and an adroit collector by giving it a certain twist completely closes the mouth, so as to prevent the escape of his captives. Fixed to a very long pole (Mr. Haworth says it should be twenty or thirty feet long[1556]), it is the best net for the purple emperor butterfly (Apatura Iris). It is also used with success to push before you through the grass of meadows, woods, &c., and thus often displaces numerous insects, which fall into it;--every now and then it is examined, and the valuable captures secured. The common bag-net will perform the same operations, but is not deep enough for flying insects. If you lengthen your stick before you screw it on, it enables you to brush with it the weeds at the sides and bottom of ditches. This employment of brushing the grass, &c. may be carried on if you are walking with any friend not interested in Entomology, without much interruption of conversation. For this last operation--sweeping the grass, &c.--if you wish at any time to devote a morning wholly to it, you will find a net invented by the late Mr. Paul, of Starston in Norfolk, and which he employs to clear his turnips of Haltica Nemorum[1557], a very useful implement. The accompanying figure will give you a better idea of it than any description[1558]; you may make it large or small according to your convenience: the wider it is, the greater space it will brush at once. When your object is a more general investigation, the bag-net just described is preferable.
4. Scarcely any implement seems a greater favourite with British collectors than what may be called the fly-net[1559]. This is universally employed by them for capturing flying insects, especially Lepidoptera. It is similar to what is called a bat-fowling net, and should be made of green or white gauze or coarse muslin. The former colour, as being less visible, is most proper for mothing in the night; but the latter is best for the day, as this net is useful to hold under the branches of trees and shrubs to receive the insects that fall when they are beaten. The rods for the net we are considering,--which should be about five feet long, half an inch in diameter at the base, and gradually tapering to the end,--must be made of some tough wood; each should consist of about four joints for the convenience of carriage, and each joint should be fitted with a socket at the lower extremity, to receive the top of the joint below it: the terminal joint must either be bent into a curve, or fitted with an angular socket or ferrule, so as to form an obtuse angle with the rest of the rod[1560]. The gauze which is to form the net, being cut into the requisite shape, should be welted round, except at the bottom, where it should have a deep fold or a bag for preventing the escape of the included insects--in order to form a slide for the rods to slip in. At the apex where they meet, a few stitches should be set, or a piece of leather sewed in, to prevent their going too far. At the bottom, on each side, two strings must be sewed on the net, to receive which there must be a hole in each rod about six inches from the bottom: these must be tied, which will keep the net from slipping upwards. When you go after moths and other insects that fly in the night, a plan, as I am told, of some of the London collectors may be adopted with advantage. Cause a lanthorn to be made with a concave back, and furnished with a reflector: this must be fastened, by means of a strap, upon the stomach. If you hold your expanded fly-net before this (as nocturnal insects fly to the light), you may thus entrap a considerable number. In sultry summer nights also, if you place a candle on a table in a summer-house, or even in a common apartment, and open the windows, you will often have excellent sport, and take insects you might otherwise never meet with.
When you use your fly-net, you must take the rods one in each hand, so as to keep it extended; and when you have brought it fairly beyond the insect you are pursuing,--to accomplish which you must be upon the alert,--you must bring the two sticks together, which, if you are commonly dexterous, will capture your prey. This net is likewise useful in taking winged insects when at rest upon the ground, by simply spreading it over them. When you use it to beat into, as above recommended, you must take both the sticks in one hand, and extend it by crossing them as much as you can. In the absence of this, a common umbrella, or even a sheet of stiff paper which you may carry folded in your pocket, are no bad substitutes. When your object is beating the bushes, bring your fly-net, &c. rapidly under the branches you mean to operate upon, or the insects will fall from them to the ground before you are prepared.
Under this head I may mention a very ingenious net for taking Lepidoptera, particularly butterflies, invented by Dr. Maclean of Colchester, which I would call Maclean's elastic net. It is constructed of two pieces of stout, split cane, connected by a joint at each end and with a rod which lies between them, in which a pulley is fixed; through this a cord fastened to the canes passes; a long cane with a ferrule receives the lower end of the rod and forms a handle; and to the canes is fastened a net of green gauze. Taking the handle in your right hand, and the string in your left, when you pull the latter the canes bend till they form a hoop, and the net appended to them is open; when your prey is in it, relax the cord, and the canes become straight and close the mouth of the net, keeping them close with your left hand, you may soon disable your prey with your right. Dr. Maclean has scarcely ever found this net fail.
5. Another instrument which should be constantly in the hands of the Entomologist is the forceps[1561]. This is particularly useful for catching Diptera and Hymenoptera chiefly while at rest on the leaves and flowers of plants. Both these tribes are usually too agile to be taken by the hand alone, which besides without this contrivance would be exposed to the stings of many of the latter. The leaves of the forceps should be octagonal, five or six inches in diameter, and covered with green gauze, or rather very fine catgut, which will enable the head of a lace-pin to pass through it. You must direct your artisan to make the joint of the handle nearer the rings for the finger and thumb than to the leaves, or the instrument will not open well. An old pair of curling-irons might be made into very good handles; but the hoop to which the catgut is fastened should be brass, or if iron it ought to be painted to secure it from rust. Some make the leaves of the forceps round; but when an insect is perched on a wall or any vertical surface, it has less chance of escape if you can apply a straight side to its station. The Germans use a much longer and larger instrument of this kind, having leaves of ten or twelve inches in diameter, which they use to catch Lepidoptera when settled on plants. When you aim at an insect with your forceps, you must expand the leaves as much as possible, and cautiously approach your prey; and when within reach, close them upon it suddenly, including the leaf or flower on which it rests. As these are sometimes bulky, and prevent the instrument from shutting closely,--that the included insect may not escape, it is often necessary to use the other hand to bring them together, when the pressure of the finger and thumb soon disables it.
6. As the waters, whether running or stagnant, as well as the earth and the air, teem with insects, you must likewise be provided with a net of a different description from any of the preceding, that you may fish them out. It may be made of fine canvass, just deep enough to prevent the insect from jumping out, and fastened to a brass hoop five or six inches in diameter, not perfectly circular, but having the segment of a circle cut off anteriorly, so that it will apply well to a flat vertical surface; and fitted posteriorly with a socket, to receive the end of your stick; or, what is better, with a screw, which will securely fasten it to it[1562]. In using this net, different modes may be adopted. You may either watch the motions of an individual insect, and secure it by darting the net beyond it and drawing it towards you; or by placing it quietly under it, and then elevating it suddenly; or you may push your net at random along the margins of the pools and rivers amongst the weeds, &c.; amongst the duck-weed (Lemna) on their surface, or the mud at the bottom; and when you examine its contents, you will often find valuable captures. I have thus sometimes got rich booty in the most unlikely places;--such as Hydræna longipalpis, and an allied nondescript species, &c.; and by fishing amongst Zanichellia palustris, Hæmonia Zosteræ. If at any time you do not happen to have your water-net with you, with a common rake you may take the duck-weed from the surface of a pool, and upon examination you will often detect amongst it many minute water-beetles.
But besides all these implements you will find your finger and thumb a very handy forceps when insects are stationary or walking upon the ground; and even when flying, minute ones that you would not otherwise meet with may be taken by the palm of your hand, wetted with saliva, if, when you see them swarming in the air, you pass it to and fro amongst them. When such are stationary, or moving on the ground, on rails, the trunks of trees, &c., the fore-finger, so wetted, will often best secure them: but if they are perched on a summit or a vertical surface, before you approach near enough to alarm them bring forward quietly your bag-net, and hold it so that they may fall into it, if they attempt by falling to escape you. Other methods of entrapping insects may also be pursued with success. A table-cloth spread on the grass in the open parts of a wood I have known allure several scarce insects: a lady's white dress is equally attractive. An old mattress, laid at night upon a grass-plat, if suddenly reversed in the morning, will supply the Entomologist occasionally with good Coleoptera. No better trap for the Silphidæ, Dermestidæ, &c., than a piece of carrion, a frog, or mole, &c. The numerous insects that inhabit excrement of every kind, especially that of the cow and the horse, may be best taken by immersing their pabulum in water: for this purpose, let a boy carry a spade and pail to the scene of action, and filling the pail nearly full of water begin the operation, and all the insects lurking in the submerged dung will come to the surface, and may be easily taken.
Another object of the collector of insects, when he has once entrapped them, is to bring them safe home. The Entomologists on the Continent, I believe, generally transfix their prey, of whatever Order, with a pin, as soon as they are caught: but as hard ones, such as Coleoptera, Hemiptera, &c., may be destroyed without injury by immersion either in spirits of wine or boiling water; and as large beetles, if transfixed (not to mention the unnecessary cruelty of so serving them), are apt to whirl round upon the pin in spite of any precaution, and injure themselves, and destroy other insects that are in their way, it seems best to kill them by other more effectual methods. With regard to those that would be injured by immersion in any fluid, as the Lepidoptera, Hymenoptera, Diptera, &c., they must be secured as soon as taken; and after having disabled them as much as you can without injuring them, by pressing the trunk below the wings with the finger and thumb, they should be transfixed and put into a pocket-box lined with cork. Some use an oblong deep chip one, with paper pasted over it, and lined at top and bottom, the top being convenient for setting small moths. But this you will find not easy to open when you have an insect in one hand; and it is too deep for the pocket. I generally use a mahogany one, about 7-1/2 inches by 4-1/2 and 1-1/4 deep in the clear, corked only at the bottom, and opening by pressing a spring, which can be done with one hand. This will contain as many of the above insects as you will usually take in a day's excursion. When travelling, you should provide yourself with larger store-boxes, to receive at night the fruit of the day's hunt. These may be 18 inches square and 2-1/2 deep, corked at top and bottom; which should be of equal depth, and fit very closely, to keep out Acari, &c. Entomologists have recourse to various ways of bringing home insects for immersion. For the larger ones, you must be provided with a number of small boxes, the lids of which are not liable to come off in the pocket. If it can be done, it is best to have only a single insect in a box. If you have several, those that are predaceous in their habits will probably devour the rest: and besides, if you open a box to put in other insects, generally one or two of those before imprisoned in it will make their escape. It is best to put the boxes containing an insect in one pocket, and the empty ones in another. If your boxes are numbered, in a small memorandum-book, which you should carry for the purpose, you may make any remarks as to the food, station, and habits of any insect you may take, inserting against them the number of the box or phial that contains it, and it will be ready for future use. For the smaller beetles, &c. a number of phials, with their rims ground down and the mouths well fitted with corks, must be provided; but for those you do not wish to keep separate, a wide-mouthed phial filled with spirits of wine, which soon kills them, is the best receptacle. I have found, when at a loss, a piece of elder, with the pith taken out to a sufficient depth at each end and each mouth stopped with a wooden plug, a useful insect box. As numerous insects inhabit the various species of Boleti, if you go where these are to be found, unless you are a very agile person and expert at climbing, a boy with a short light ladder will be no useless accompaniment.
Something may be said in this place upon the dress with which the Entomologist should provide himself. I shall not recommend to you, in imitation of the insect-hunters in the vignette to Reaumur's second volume, to put on a bag-wig and a velvet court-dress; but the plain fustian jacket with side and other pockets used by English sportsmen will very well suit your purpose; only let the pockets be sufficiently ample: have also an inside one fixed on the left-hand side to receive your forceps. You may also have a bag like a shooter's, or an angler's basket, which may contain your nets till you want to use them. With all your implements about you, you will perhaps at first be stared and grinned at by the vulgar; but they will soon become reconciled to you, and regard you no more than your brethren of the angle and of the gun. Things that are unusual are too often esteemed ridiculous; and the philosopher whose object is to collect and study the wonderful works of his CREATOR, is often regarded by the ignorant plebeian as little short of a madman.
Such is the apparatus to be provided by the entomological Nimrod: it is not often, however, that it will be necessary, except in distant excursions, to encumber and disfigure yourself with the whole. Even in this pursuit more may be effected by a judicious division of labour, than by grasping at every thing at once; and your acquisitions will in the end be more numerous, and your acquaintance with them more intimate, if at one time you devote yourself to the woods and hedges, another to the plains and meadows, a third to any heaths in your vicinity, and a fourth to the collection of aquatic insects whether from stagnant or running waters:--having thus chosen the scene of action, you may equip yourself accordingly. You will of course, though in pursuit of a particular description of game, not neglect to seize any other insects that fall in your way; but for this purpose it is unnecessary to be always provided with a certain instrument. Dr. Franklin used to say that a man would never make a Natural Philosopher, who, in performing his experiments, could not saw with a gimblet or bore with a saw; and so we may say, he will never make an expert collector of insects, who on occasion cannot fish with his hand or forceps, use his hat or an old letter to beat his game into, or, in the absence of boxes or bottles, contrive to secure his captures in small pieces of paper twisted up. Sparrman, when at the Cape, was wont,--to the no small amazement of the wondering natives, who took him for a conjurer,--to stick his impaled insects round the outside of his hat[1563]: and though I should not recommend such an exhibition in a civilized region, it has often struck me that the cavity of a modern hat, if lined with cork, might be made a very useful receptacle for these animals in a long excursion. Indeed, an active Entomologist is never at a loss for an apparatus, but often makes his most valuable captures when unprovided with other instruments than his hands and eyes. A careful survey of the trunk and branches of trees and shrubs, particularly of the underside of their leaves, seldom fails to detect many a lurking moth or beetle, which may be transfixed or otherwise captured with little trouble by an expert hand. In this way an ingenious collector, who scarcely knew what a net of any kind was, told me he had made his whole collection, which was rather extensive. It is, in fact, only by thus detecting them when reposing, and adroitly shutting them up along with the leaf on which they sit, in a box, that minute moths (whose beauty and freshness the slightest handling destroys) can ordinarily be taken without being injured. The boxes containing them should afterwards be exposed to the action of heat, a low degree of which will destroy them.
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Enough has been said upon the best modes of catching insects:--I shall next attempt to give you some further instructions as to the most effectual one of destroying them when caught, and to point out how you are to proceed with them after they are dead. As I sufficiently rebutted the charge of cruelty in a former letter[1564], it will not be necessary to enter here into that subject.
I have before recommended to you the use of spirits of wine, and shall here repeat my recommendation; for after several years trial, I am of Böhm's opinion, who had tried it nine years[1565], that it is superior to any other method; particularly, because it not only effectually kills the insects, and they may be put together into it while you are collecting, if you have no reason for keeping them separate, of all sorts and sizes, in a wide-mouthed phial, without danger of their devouring each other: but when you come home wearied with a long day's hunt, you may let your insects remain in it without injury till the next morning. In collecting beetles abroad, when there is a want of store-boxes the readiest way is to put them into a wide-mouthed bottle or jar filled with any spirit, and send them home in it: some few may lose their colours, or become greasy; but in general they will receive little injury. This method saves room, and avoids the risk of breakage. The derangement which some hairy species sustain from this method may be readily repaired by brushing them with a dry camel's-hair pencil.
When you wish to take the insects you have immersed in spirits out of the phial, you must strain its contents through a piece of muslin, return the spirit into it for future use, and spread the insects separately upon blotting-paper, to absorb the moisture remaining about them. With regard to such as you have in boxes or phials without spirit, these must be immersed in a basin of boiling water. First empty into it the contents of your boxes, and next, those of your phials; giving each, before you take out the cork, a smart rap, that the insects adhering to the latter may drop to the bottom: or you may immerse the phial itself, with the cork in, which soon destroys them, and is the safest plan. This done, with a camel's-hair pencil or feather take them out of the water, lay them upon blotting-paper to dry, and put them by for a few hours till you have leisure to impale and set them.
Those insects that are caught by the forceps would for the most part escape you, were you to attempt to get them out before you had transfixed them. You must therefore do this while the leaves of the instrument are closed; and then opening them, and taking the pin by the point, the head will readily pass through the catgut; and thus you may safely take, and more effectually kill your specimen by pressing it as before directed. With respect to Lepidoptera, it is necessary to disable them while yet in the fly-net, immediately after their capture. To effect this, while one hand holds both the rods of the closed net, with the other stretch the gauze so as to confine your insect within a narrow space; bring its wings into an erect position, and prevent its fluttering: which being done, with your finger and thumb give its breast a strong pinch below the wings; and then unfolding your net, and taking it up by one of its antennæ, place it between the finger and thumb of your left hand, stick a pin through it, and deposit it in your pocket-box.
But though nipping the breast will kill many small Lepidoptera, the larger ones will live long after it; as will likewise many Neuroptera, Hymenoptera, and Diptera: and besides this, in some Bombycidæ the thorax presents a very conspicuous and interesting character, which renders it desirable, in order to avoid the damage or derangement occasioned by pressure, to transfix them without it. To dispatch these effectually, you will find the following apparatus very convenient. Fix in a small tin saucepan[1566] filled with boiling water, a tin tube consisting of two pieces[1567] that fit into each other; cover the mouth of the lower one[1568] with a piece of gauze or canvass, and place your insects upon it; then fix the upper one[1569] over it, and cover also the mouth of this with gauze, &c.; and the steam from the boiling water will effectually kill your insects without injuring their plumage. There is another more simple mode of doing this, the apparatus for which may be met with every where. Fix a piece or two of elder, willow, or any soft wood, with the bark on, across the bottom of a mug, and on this stick your impaled insects; invert the mug in a deep basin, into which pour boiling water till it is covered, holding it down with a knife, &c., that the expansion of the included air may not overturn it. In two minutes, or less, all the insects will be found quite dead, and not at all wetted. If the sticks do not exactly fit, they may be wedged in with a piece of cork. Professor Peck, who used to put minute insects into the hollow of a quill stopped with a piece of wood made to fit, killed them instantaneously by holding it over the flame of a candle.
Having killed your insects, your next object should be to prepare them for your cabinet. First, place by you a pincushion well stored with lace-pins of various magnitudes and lengths: for most insects those nearly an inch in length, for large ones, those that are thicker and longer, but for Lepidoptera, a stouter kind, as short whites, are best. Next, take the Coleoptera and Hemiptera that, as before directed, you have laid by on blotting-paper after immersion, and begin your operations, selecting the largest first. The pin should be stuck through the middle of the right-hand elytrum[1570], and about one third of its whole length should emerge above the insect. Some foreign collectors, probably having in view its more convenient examination with a microscope under the glass of a drawer, bring it nearer the head of the pin: while the English ones, on the contrary, studying the most ornamental position of their specimens, leave only enough of the point free to fix them safely in their drawers[1571]. Both these methods are open to objection. When the insect is too near the head of the pin, it is difficult to fix it in your cabinet without bending the wire; and there is danger, without great care, of injuring the specimen when you put it in or take it out. Again: When the legs of your insect rest on the surface they collect the dust and dirt, are very liable to be broken, and the length of the pin above it is inconvenient when you have occasion to examine any one under a lens. Lepidoptera, however, which are never thus examined, may always be transfixed in this way, which sets them off to the greatest advantage.
Some insects, especially of the beetle tribe, are so extremely minute that it is next to an impossibility to get a pin through them without injuring, and often destroying them. By using fine needles, or very slender pins manufactured on purpose, this difficulty might perhaps be surmounted; but the needles will be subject to rust, and the pins, I know by experience, cannot be fixed in cork without difficulty. For such minute insects, therefore, by far the best mode is to gum them on small pieces of card, which may be stuck upon a pin. Talc, which admits the underside of an insect to be seen through it, has been used for this purpose; and where you have only a single specimen, a thin small lamina of it would answer well; but ordinarily I should recommend the former mode. Your pieces of card, which must be small, may be either oblong and cut at the corners for neatness, with a couple of specimens gummed upon each, one on its belly and the other on its back; or you may cut little narrow card wedges, about four lines long and terminating in a point, upon which you may so gum your insects as to show the principal part of the under side, as well as the upper side of its body. Common gum-water made rather thin, with a very little glue mixed with it, will answer your purpose very well: it should be thinly spread on the card with a camel's-hair pencil, and then the insect placed upon it. With the same implement, if it has not been killed too long, before the gum is dry you may expand its antennæ, palpi, legs, and wings, &c. If you want to remove a specimen gummed on a card for any purpose, it is easily effected by plunging it into hot water.
Other insects may be transfixed through the thorax or upper side of the trunk; as also those Coleoptera, Orthoptera, and Hemiptera, whose wings you are desirous of expanding; only you should be careful that your pin passes through them behind the prothorax.
Having impaled your insects, the next thing to be done is to set them. The best time for doing this is not till they have begun to stiffen, but before they are become quite stiff. If attempted soon after they are killed, the parts, unless you keep them in the intended position by means of pins or braces, will not retain it; and if after they are become too stiff, they are liable to be broken. Not only should the antennæ and palpi be extended so as to be readily seen; but the legs, and often the wings, ought to be placed in their natural position; all of which tends much to the beauty of your specimens, and adapts them for more ready examination. But as this operation requires time, and beauty and regularity may be purchased too dear if at the price of hours called for by science, you may be left to your own discretion in this business, only you should always with a pin expand the antennæ and palpi if possible. You might, however, both save your time and have your insects neatly set, if you would take the trouble to instruct some acute and handy youth in your neighbourhood in the modus operandi, and devolve this department upon him: and as none are quicker and more expert in capturing insects than boys, he might also assist you in your hunting expeditions.
I do not mean, however, to leave you at liberty with regard to the setting of Lepidopterous insects, which not only have a much worse appearance than those of other Orders if their wings be not regularly and uniformly expanded, but require it for the proper display of their characters. The necessary apparatus consists of a piece of cork about nine inches long, four broad, and half an inch thick, which should be made perfectly smooth, with a piece of white paper pasted over it; and of several narrow slips of card or braces, tapering gradually to a point, of different lengths, from half an inch to two inches or more, with a pin fixed in each at the broadest end. Thus provided, you may proceed to action. But you must first decide whether, like the continental Entomologists, you will set your Lepidoptera horizontally; or, like the British, with their wings declining obliquely from the body. If you prefer the former method, the body must be let into a groove, and the wings expanded as flatly as possible, the anterior margin of the primary pair being brought forward so as to project beyond the head. But as this usually gives the insect an unnatural and formal appearance, I apprehend a man of your taste will prefer the mode adopted by your compatriots, the collectors of Britain, who in setting make the wings form an angle, varying according to the size and characters of the insect, with the body, and do not bring the anterior wings so forward. The wings of butterflies however, in order to appear at all natural, should be set more horizontally. Which fashion soever you prefer, the mode of operating is nearly the same; only that the English plan, except in the case of some large-bodied moths or hawk-moths, requires no groove in the setting-board. After you have stuck the insect upon the cork so as to bring its body close to its surface, stretch the anterior wing with a needle fixed in a handle, or a camel's-hair pencil, applied to the joint at the base, sufficiently forward, and then confine it by means of one of your card braces:--next, do the same by the opposite wing. Afterwards expand the posterior wings, which must not be separated from the anterior so as to leave any interval between them, and fix them with braces. When you are become expert, you will find, if the fly is not large, that a single brace will be sufficient for each pair of wings[1572]: but sometimes, if the card be not sufficiently stiff, you may confine it by a pin near the point. You must be careful in expanding the wings that each is brought equally forward. Lastly, give the antennæ their proper position, and if necessary confine them with braces; and leave your specimen in an airy situation to dry and stiffen. In a few days the braces may be removed, and the specimen transferred to the cabinet. When you put them away to become stiff, you must be careful to place them and your other insects at night where earwigs cannot come at them; for in sultry weather these animals will often then attack and spoil them.
It is obvious that this process can only be performed while the joints and ligaments of the insect are still flexible; so that small species, in warm weather, will often be immoveably rigid before you can have an opportunity of setting them. On this account collectors usually set minute moths as soon as taken, which can be readily done on the lid of a cork-lined box. But fortunately both these, and specimens which have been dried for years, may be relaxed and rendered pliable by a very simple process. Fill a basin more than half full of sand, and saturate it with water; pour off the superfluous water, and cover the sand with blotting-paper: into this stick the insects you wish to relax, and covering the basin closely, leave them there for two or three days, according to their size; and the evaporation will render them sufficiently flexible for expansion or any other purpose. Beetles may be relaxed by plunging them for a short time in warm water or spirits of wine[1573].
Many moths of the tribe of Tinea L. are so extremely minute, that it is almost impossible to set them without defacing their characters: indeed, the trunk of some is so small as not to admit being pierced by a pin. These, therefore, it is adviseable merely to gum upon card, expanding their wings (which the gum will easily retain in their proper situation) with a camel's-hair pencil. If you have two specimens, you may fix one in the natural position when at rest,--a method I should recommend with respect to other Lepidoptera, and indeed insects in general. Pezold advises that, by way of contrast, white card should be used for dark-coloured species of these little moths, and black for such as are pale. As the wings of different Coleopterous groups, as well as those of Hymenoptera, Diptera, &c., vary in their neuration[1574], you should, whenever you can, set open the elytra and expand the wings of one specimen at least in each group, which will be very important to you in making out the characters of your genera.
When sufficiently dried, your insects should be transferred from the setting-boards, either to their place in your cabinet or to the store-box before described, till you have leisure to investigate them.
However tedious some of the foregoing manipulations may seem, they are in fact much less so than those required in several other branches of Natural History, where, in addition to the labour of catching, the nice and difficult task of clearing the skeleton of its muscular covering, and its internal cavity of its contents, and then of stuffing it and replacing its perished eyes by glass ones of the proper colour, is a necessary process with every individual. Happily the Entomologist, from the smallness of his game and the nature of their integument, is usually spared this labour. There are some few insects, however, in which a process in some degree analogous is requisite, if the beauty of the specimens be a consideration. Thus the abdomen of dragon-flies is very apt to lose its colour, and that of the Meloës to shrink up, if left in their natural state: these therefore should be eviscerated; which may be done by slitting the abdomen longitudinally on the under side, then carefully removing its contents, and stuffing it with cotton. In the former, a small straw or stalk of hay may be used, which will prevent the fractures to which that part, when dry, is so liable. Spiders, and a few apterous genera, as well as almost all larvæ, as they usually shrink up, in drying, into a shapeless mass, destitute of every character dependent on colour or form, require to be preserved in a different manner. They may all be very well kept in rectified spirits of wine mixed with water, in the proportion of three parts of the former to one of the latter. Each, suspended by a thread, should be put in a separate very small labelled phial. Larger spiders, such as Mygale aviculare, &c., when suffered to dry, though the abdomen shrinks, do not wholly lose their characters, and are often kept in cabinets: but if preserved in spirits, they may be put into larger wide-mouthed bottles, suspended at different heights, with a label on the outside opposite to each species. Mr. Abbott of Georgia had an excellent method of preserving caterpillars, so that his specimens retain their colours and other attributes, and look as if they were alive. I am not acquainted with his process, but the following will answer very well.--The animal must first be killed by immersion in spirits of wine; next you must eviscerate it, which is best effected by gradual pressure of the finger and thumb. You must begin at the head, and so proceed till all the fluid contents of the body have passed out at the anus, which you may enlarge with a fine pair of scissors, being careful not to injure the anal prolegs. When you have cleared the skin as much as possible, introduce a fine glass tube, or a piece of hay or slender straw into the anus, round which, as near to the extremity as may be, pass loosely a fine thread: then blowing through the tube, when the skin is fully inflated withdraw it, at the same time pulling the thread tight and securing it by a knot. The caterpillar will now exhibit its proper shape and colours; to retain which, all that is necessary is to hold it near the flame of a lamp until perfectly dry, which will be in a few minutes, when it may be placed in the cabinet along with the imago to which it belongs[1575].
* * * * *
Although a very large proportion of the insect inhabitants of any country may be captured in their perfect state by the active Entomologist, yet there is no small number of them that probably he may never meet with in that state, and to secure which he must have recourse to other methods. He can procure pupæ by digging for them in woods, under trees, &c., as above directed[1576], keeping them in some of their native earth till they are disclosed; or he must collect larvæ, and breed them; for which I shall now give you some instructions.--The insects we are particularly concerned with under this head are the caterpillars of Lepidoptera and of the saw-flies (Serrifera). If, however, in our entomological rambles we discover the larvæ of insects of other Orders upon their appropriate food, we may often attempt to breed them with success: but as you will seldom thus get species that you will not also meet with in their imago state, and the general directions for breeding will include almost all, I shall principally consider the best mode of breeding caterpillars, and pseudo-caterpillars. The first thing is to collect them. In beating the trees, bushes, and plants, while hunting for Coleoptera, &c., the Entomologist will often displace caterpillars, which, if unknown, he should put into a pill-box with a portion of their food: but Lepidopterists often sally into the woods, &c., for the express purpose of collecting these only. When engaged in this employment, the best plan is to take a sheet with you, and when you mean to beat the branches of any tree, place it as near them as you can, upon four or more sticks fastened in the ground, so as to leave the upper surface concave, and it will receive the falling caterpillars when you beat. If you aim at the pseudo-caterpillars of the Cimbicidæ, you must turn your attention principally to the different species of sallows and willows (Salix). Your spoils you will put into boxes with their food, as above directed, to bring them home.
There are several kinds of boxes recommended to receive them and breed them in. If your only object is to get the perfect insect, a cubical box of moderate dimensions, glazed in front or on one side to enable you to watch their proceedings, with the other sides and top fitted with fine canvass for the admission of air, will very well answer this purpose; or your box may be canvassed all round, with a door in front[1577]. In this you may place a small garden-pot filled with earth, with a phial of water plunged in it to receive the insects' food. This may be moved, when you wish to change the water, without disturbing the earth, which should be kept somewhat moist. The earth is for those caterpillars whose pupæ are subterranean. But as you will probably wish to proceed scientifically, and ascertain precisely the moth that comes from each caterpillar, I should strongly recommend to you a box invented by Mr. Stephens, which he describes in a letter to me in nearly these words:--"The length of the box is 20 inches, height 12, and breadth 6; and it is divided into five compartments. Its lower half is constructed intirely of wood, and the upper of coarse gauze stretched upon wooden or wire frames: each compartment has a separate door, and is moreover furnished with a phial in the centre for the purpose of containing water, in which the food is kept fresh; and is half-filled with a mixture of fine earth and the dust from the inside of rotten trees; the latter article being added for the purpose of rendering the former less binding upon the pupæ, as well as being highly important for the use of such larvæ as construct their cocoons of rotten wood. The chief advantages of a breeding cage of the above construction are, the occupation of less room than five separate cages, and a diminution of expense; both important considerations when any person is engaged extensively in rearing insects. Whatever be the construction of the box, it is highly necessary that the larvæ be constantly supplied with fresh food, and that the earth at the bottom should be kept damp. To accomplish the latter object, I keep a thick layer of moss upon the surface, which I take out occasionally (perhaps once a week during hot weather, and once a fortnight or three weeks in winter), and saturate completely with water, and return it to its place: this keeps up a sufficient supply of moisture, without allowing the earth to become too wet, which is equally injurious to the pupæ with too much aridity. By numbering the cells, and keeping a register corresponding with the numbers, the history of any particular larva or brood may be traced."
In attending to your insects in their cells, your expectations will sometimes be disappointed, when, instead of a butterfly or moth, you find only an Ichneumon. But this you must not regard as all misfortune; for by this means you will be better instructed in the history of each species, and learn to the attack of what enemies it is exposed: and thus you may get many species of these parasitic devourers of insects that you would not elsewhere meet with. If your caterpillars, however, appear to be of a rare kind, you must watch, and often examine them; and if you discover black specks upon any one, that appear unnatural or like nits, they may be extracted, Mr. Haworth assures us[1578], by a pair of small pliers; and if the operation is adroitly performed, the caterpillar will recover and do well. You will often meet Lepidopterous larvæ travelling over roads and pathways: at such times they have usually done feeding, and are seeking a spot in which they may assume the pupa with safety. These you may place in one of your cells, and they will select a station for themselves. You must be careful frequently to examine the boxes in which you have pupæ, that you may take the imago as soon as it appears, and before it has had time to injure itself in attempting to escape. I mentioned to you on a former occasion Reaumur's experiments to accelerate the appearance of the butterfly[1579];--there is another still more remarkable, to which he had recourse for this purpose: it was by hatching his pupæ under a hen!! You will wonder, perhaps, how this could be effected, and be disposed to maintain that the pupæ must be crushed by the weight of the brooding animal. How did the ingenious and illustrious experimentalist prevent this? He prepared a hollow ball of glass, open at one end, about the shape and size of a turkey's egg. Having several chrysalises of the nettle-butterfly (Vanessa Urticæ) suspended to a piece of paper, he cut out some of these singly, with a square portion of the paper attached to them, and covered with paste the side opposite to that from which the chrysalis was suspended: these he introduced into the ball through the aperture, placing them as near to each other as possible, taking care so to apply the pasted surface to the inside of the ball, that when the side to which they were fixed was uppermost they all hung as from a vault. This being done, he stopped the aperture with a linen plug, but not so completely as to cut off all communication with the atmosphere: he next placed the egg under a hen that had been sitting some days, who always kept it at the side of the nest, where it nevertheless derived benefit from her incubation. After the first day its interior was covered with vapour transpired by the chrysalises. Upon this Reaumur took the egg, and removing the linen plug it soon became dry again: he replaced it under the hen, and no vapour afterwards appeared. In about four days the first butterfly ever hatched under a hen made its appearance; it would probably have required fourteen under ordinary circumstances. He tried the same experiment with some Dipterous pupæ; but the heat was too great for them, and they all perished[1580].
* * * * *
Having properly prepared and set your specimens as above directed, the next step, when they have remained a sufficient time to be perfectly dry, is to place them in your cabinet. If you collect foreign insects as well as British, you may either preserve the latter in a separate cabinet, or keep both in the same, distinguishing the indigenous species by a particular mark. The letter B in red ink, if the pin which transfixes the insect be run through it, or, in the case of Lepidoptera, placed before the specimen, would be a very distinct and sufficient indication of them. The drawers of your cabinets should be about 18 inches square, and from the glass to the corked bottom about an inch and a half in depth: but the larger Dynastidæ, as Megasoma Actæon, &c., will require two inches. The frame of the glass should be rabbeted underneath; and parallel with the sides of the drawer, but a little lower, there should be inner side-pieces fixed, so as to form a cavity all round of a proper width to closely receive the rabbet, and likewise to contain the camphor for preserving your insects from the attack of mites, &c.; to emit the scent of which, many holes should be bored in the side-pieces. Each cabinet may contain forty of these drawers in a double series, protected by folding doors; and you may place one cabinet upon another, if your space admits it. You will find a tool used by bell-hangers for cutting their wire very convenient to behead or otherwise curtail the pins, as those with which foreign insects are transfixed are often too long. If you cut them off below the insect, cut them obliquely, which will leave a point that will enter the cork.
When your drawers are smoothly corked[1581] and neatly papered, first divide each transversely by a full black line; parallel with this, on each side, draw a line with red ink: then, for arranging your insects, draw pencil lines, which are easily obliterated, at right angles with the others, according to the general size of the insects that are to occupy them. Insects look better thus arranged in double columns, than if the pencil lines traversed the whole width of the drawers. In arranging them, you may either place them in a straight line between the pencil lines,--which I think is best,--or upon them. You will begin your columns from the red lines in the middle, and not from the sides of the drawer; thus the heads of those on one side of it will be in an opposite direction to those on the other. Where your pins are very fine and weak, you must make a hole first with a common lace-pin; otherwise, in forcing them into the cork, they will bend. In labelling your specimens, you should stick the appellation of the genus or subgenus with a pin before the species that belong to it. As to the species themselves, you may either number them 1, 2, 3, &c., sticking the pin they are upon through the number, and denoting them by a corresponding one in your catalogue; or you may at once write the trivial name, with the initial of the genus upon a label transfixed in the same manner. Lepidoptera cannot easily be arranged in columns. Perhaps if squares, corresponding with the size and number of the specimens of any given species you wish to preserve, were made with pencil, a label of the trivial name of the species, or a number being placed at its head, it would be as good a way as any other. But every one must be left to his own taste in these matters. Wherever you can, procure a specimen of each sex of an insect, and where important characters require it, let some of your Lepidopterous specimens exhibit the under side of the wings.
In arranging insects in your cabinet, if you wish to have it scientific, as much as the nature of the subject will admit, follow the series of affinities; but you may reserve a few drawers to place in contrast analogous forms. As your numbers of species increase you will have to alter your arrangement; but as pencil lines are easily rubbed out, this will occasion you less trouble than if they were drawn with ink. You should always be careful under each genus to leave space for new species.
As certain Acarina, Tineidæ, Ptinidæ, &c., prey upon dead insects, you will of course wish to know how they may be kept out of your drawers, or banished when detected there. Camphor is the general remedy recommended. The cavity closed by the rabbet of the glass frame affords a good receptacle for this necessary article: put some roughly powdered into each side, and be careful to renew it when evaporated. This will generally preserve your insects, as will be seen from the result of the following experiment.--Some insects in a chip box having become much infested by mites and Psocus pulsatorius, I placed under a wine-glass several of each along with roughly-powdered camphor: at the end of twenty-four hours the mites were alive; but at the end of forty-eight they were all apparently dead, and did not revive upon the removal of the camphor. The specimens of Psocus all appeared dead in an hour, and never revived. If the camphor be put only into one side of a drawer, and in a lump, though perhaps it may keep out mites, &c., it will not expel them.
I am, &c.
FOOTNOTES:
[1554] Entomologist's Useful Compendium. t. xi. f. 5.
[1555] PLATE XXIV. FIG. 1.
[1556] Lepidopt. Britann. 20.
[1557] VOL. I. p. 187.
[1558] PLATE XXIV. FIG. 3.
[1559] PLATE XXIV. FIG. 4.
[1560] Samouelle's Compendium. t. xi. f. 1, 2.
[1561] PLATE XXIV. FIG. 5.
[1562] PLATE XXIV. FIG. 2. N.B. The net is represented too shallow in this figure.
[1563] Voyage to the Cape. i. 63. Eng. Trans.
[1564] LETTER II.
[1565] Illig. Mag. iii. 222. Mr. Stephens however, whose experience is great in the best modes of collecting, is of opinion that insects that have been immersed in spirits of wine are apt to become mouldy. We have not ourselves observed this.
[1566] PLATE XXIV. FIG. 7. c.
[1567] Ibid. a, b.
[1568] Ibid. b.
[1569] Ibid. a.
[1570] PLATE XXIV. FIG. 8.
[1571] In the figure just quoted the artist has represented the insect as transfixed in this way.
[1572] PLATE XXIV. FIG. 9.
[1573] Mr. Samouelle (Useful Compendium, 321) recommends a somewhat different method.
[1574] VOL. III. p. 623--.
[1575] Some other methods are recommended by Mr. Samouelle, which the reader will find in his Useful Compendium, 318.
[1576] See above, p. 529.
[1577] PLATE XXIV. FIG. 6.
[1578] Lepidopt. Britann. 87.
[1579] VOL. III. p. 262--.
[1580] Reaumur ii. 12--.
[1581] See Mr. Samouelle's Compendium, 311.
Letter LI
INVESTIGATION OF INSECTS.
An entomologist who aspires to more than the character of a mere amateur, will not be content with filling his cabinet with nameless objects for the sole amusement of the eye; but will also be anxious to acquire some knowledge of what he has collected, and to ascertain by what names, whether indicating their genus or species, they have been distinguished by scientific writers who have described insects either in general or those of particular districts. Thus only can he himself derive profit from any discoveries he may make, or contribute to the further progress of the science[1582].
But in order to accomplish this object effectually, you must remember and practise the Onslow motto--Festina lente:--you must not be too eager to name your species, but begin first with grouping your collection. The only way to acquire, in any degree, a correct knowledge of the Natural System, or of the general plan of the CREATOR, which is the primum and ultimum of true science, is by studying groups. The knowledge of species is indeed indispensable for the registry of facts and other practical purposes, but the knowledge of groups leads to a higher wisdom; and indeed it is through these that we best descend to the study of species.
I will suppose you have made yourself master of so much of the technical language, particularly the names and most important attributes of the principal organs of insects, as will suffice for understanding descriptions, or knowing these parts when you see them. I will also further suppose that what was formerly said on these subjects has been sufficiently studied, to enable you without much difficulty or hesitation to say whether any given object belongs to the Class Insecta or Arachnida, or to which of their respective Orders[1583]. You are therefore qualified to arrange your collection into its primary groups. But you have seen that many others intervene between the Order and the genus or species. As the genera of Linné are mostly primary groups of Orders, perhaps, setting aside such insects included in them by him as your eye and their apparent characters convince you have no claim to a place there, your next best step would be to make yourself thoroughly acquainted with them. When you have accurately marshalled and intimately studied these groups, you will probably have acquired an eye and a tact, experto crede, for grouping without book, and may proceed by analysis to resolve your whole collection, as nearly as possible, into as many as nature seems to indicate to you. In doing this you will doubtless at first fall into many errors; but these, practice and a closer examination will in time enable you to rectify. Having thus got your groups as near to nature as you can, you may now have recourse to those authors, particularly Fabricius and Latreille, who have subdivided the genera of Linné; and you will see which of your groups agree with theirs, detect your own errors, and often theirs, and be enabled to label each of your genera and higher groups, if already known, with its modern appellation. You are now qualified also to enter scientifically into the study of the characters that distinguish groups, and may proceed, wherever opportunity is afforded, to examine the trophi, which may often be displayed sufficiently by the means recommended in my last letter[1584]. In this way you may learn also to know your groups as well by character as by habit, and be qualified to trace the gradual progress of nature from form to form; and may look upon yourself as duly prepared to put the last hand to your labours, and proceed to the examination of species.
It will have occurred to you, in making out your genera or lowest groups, that some consist of a vastly greater number of species than others. It seems advisable therefore, when you apply yourself seriously to ascertain what described ones your cabinet contains, to begin with those genera which appear to be poor in them; for here your labour will be comparatively light, from the small number you will have to examine; and you will become practised in the employment before you are called upon to attack those that overflow. Had Fabricius and other describers of species taken the trouble to subdivide the larger groups, as might easily have been done, into more genera and subgenera, the student would have been spared a most discouraging labour. To be obliged to compare a single individual with the descriptions of from 100 to 300 species[1585], to ascertain its name, seems enough to make you start aside with horror from the employment, and be content that your species should remain unnamed, rather than expose yourself to such a waste of time and patience. But to lessen your alarm and encourage you to proceed, I must observe to you, though in a few instances it may be necessary to advert to the description of every single species in a section, yet that this is seldom requisite; and where it is, there are many helps to diminish the labour and abridge the process. A large number of insects are characterized by their colour; and it is the practice of all good describers to begin their definition of the species with that which predominates, and then to enumerate the variations from it. Thus, if an insect be all black except the thorax, antennæ, and legs, you will find it thus characterized, "Black: with thorax, antennæ, and legs ferruginous"; and so on. Hence, having noticed the predominant colour of your unknown species, in many genera you may compare it with the descriptions contained in a whole page at a single glance, and only read the further descriptions when the colour agrees. A practised Entomologist will thus investigate his insects with a rapidity which to an unlearned bystander would seem impossible. Though I have instanced colour as being the character most commonly employed in describing species of insects, you will readily conceive that in some tribes other characters afford more prominent distinctions. Thus in the Dynastidæ and many other Petalocerous beetles, the principal specific character is derived from the horns or tubercles that arm the head and thorax: in Lucanus from the mandibulæ; and in Prionus from the marginal teeth of the thorax. If the insect, then, you want to name belongs to any of these genera, having observed its peculiar characters in this respect, you may ascertain in a very few minutes whether any already described exhibit the same. This facility of investigation can be better acquired by practice than precept, and cannot be attained all at once. The above hints, however, may be of some use; and cannot fail to be so, if you always endeavour to make yourself acquainted by a previous careful examination with the characters of every new insect you acquire,--whether those of form, colour, or sculpture,--before you attempt to discover its name in Fabricius or any other author.
When you have made such proficiency in the study as to be familiar with a few species of each section of an extensive genus, the labour of investigation will sometimes be greatly facilitated by attending to that conformity between the proportions, general aspect, and figure of a known and an unknown insect, which Naturalists express by the name of habit, and which, though easily perceived by a practised eye, is described with such difficulty. Scientific Entomologists in their descriptions have usually taken care to place near to each other, species agreeing in habit. When therefore you know the name of one species, and find another of the same general habit, you may commonly take it for granted that if described at all by your author, it will be placed near that already known to you. Thus, supposing you are acquainted with that common weevil Cionus Scrophulariæ, and find its near relation C. Blattariæ; instead of comparing it one by one with the 161 species which compose the Longirostres femoribus dentatis of the Fabrician genus Rhynchænus in the Systema Eleutheratorum, you would at once turn to the former, very near which you would without further trouble discover it. Fortunate, would it be, could the Entomologist always depend on thus finding descriptions of allied species in the neighbourhood of each other; but unhappily the most distinguished authors have sometimes violated this important rule, so that we cannot always be certain that any given species is not elsewhere described than in its right place. Fabricius in many instances often removes widely asunder insects not merely related, but which are in reality scarcely more than varieties of the same species[1586]. In fact, the attention of this celebrated author was so distracted by the immensity of the materials he had to arrange, by the distance of the cabinets, in many cases, from each other, the new species of which he undertook to describe, and the rapidity with which they necessarily passed under his eye, that he seems never to have attained any nice perception of the affinities of insects.
You must not conclude, however, that the investigation of a new insect is even to an adept always a work of ease and dispatch. Often, when seemingly ascertained by the rapid process above indicated, a further inquiry will be requisite; the more detailed description must be read, and figures consulted, before its name can be indisputably determined. In addition to the difficulty arising from the insufficient characters frequently given by Fabricius and the older authors, obstacles arising from their errors not seldom intervene. Thus they have sometimes selected for a specific character,--as in the case of Megachile centuncularis, Nomada ruficornis, and various other insects,--what really only indicates a family. At other times sexual characters common to many,--as in Eucera longicornis, Locusta perspicillata, &c.,--have been had recourse to. In these cases, in order satisfactorily to ascertain your species, you must further consult the synonyms and habitat given by the original describer, especially the figures he has referred to. When all these fail, as they sometimes will, the dernier resort is a reference to the cabinet containing the original specimen from which the description was drawn. British Entomologists possess an invaluable privilege, which their continental brethren may well envy them, in having the most liberal access, indulged to them by the learned President of the Linnean Society, to Linné's collection of insects, from which a large proportion of the species he described may be ascertained[1587]. Several of the cabinets, especially the Banksian,--now the property of the Linnean Society,--from which Fabricius described his insects, may also still be consulted; and thus many mistakes rectified, which would otherwise greatly mislead[1588].
Though sometimes the limits that separate good species appear at first very slight, and require a practised eye to catch them, yet it occasionally happens that considerable apparent differences may safely be disregarded. The colour of insects,--to which unhappily for want of better characters we are so generally forced to have recourse,--though usually constant, is in some species very variable[1589]. This is the case sometimes with whole colours. Thus Carabus arvensis, Pœcilus cupreus, &c., are sometimes of a copper colour; at others, resemble brass; at others, they are green or blue, and even black. The colour of spots also often varies. In some individuals of Pentatoma oleracea they are pale, and in others red. The number and shape of spots are also often inconstant. Many of the species of Coccinella so abound in these variations, that nothing short of the most careful examination can enable you to distinguish the species from the variety. Insects vary also in size: but as this is never assumed as a specific character, it will not occasion you much trouble. Where the difference in this respect between two specimens is very great, the presumption is that they are specifically distinct. Differences in sculpture and proportion do not always indicate different species; this being sometimes, as we have seen above, only a sexual character[1590]. Authors also in their descriptions, in this respect sometimes mislead the young student. When Linné calls the thorax of Aphodius erraticus smooth (lævis) he would not expect to find it covered with impressed puncta, and with a longitudinal posterior impressed line. Likewise in describing Chlænius vestitus and nigricornis, Fabricius passes without notice their punctate surface, so different from that of other Harpalidæ. Errors of this kind however, it is but fair to observe, are chiefly to be attributed to the circumstance that both Linné and Fabricius rarely employed a microscope in making descriptions; though no one now attempts this, except where insects are large, without such an aid.
If you ask, How am I to acquire this delicacy of tact which is to decide when the terms of a specific character are to be rigidly adhered to, and when taken with a certain latitude? I answer, In the same way in which a connoisseur attains the faculty of discerning the works of different masters in painting;--by such careful study of your author as will make you master of his style. Thus you will soon perceive in what cases expressions are to be taken literally and strictly, or with some allowance and abatement.
There yet remains more distinctly to be adverted to, the assistance that may be derived in the investigation of insects from figures. Generally speaking, these should never be referred to in the first instance, but be regarded as a resource when the ordinary methods leave the subject of inquiry doubtful. Those who begin their entomological studies by turning over figures usually end them there, and never attain to that nameless tact in making out insects that can only be the result of patient study. Indeed figures, though often very useful, and sometimes indispensable, can scarcely ever exhibit those nice characters, particularly as to sculpture, that distinguish some insects. Our modern artists, indeed, are remedying this defect of the art, by giving in many cases the thorax or elytrum apart, with all its sculptural peculiarities: but this is not, and cannot be, done so as to represent every one. But though in general figures should be your last resort, I know not whether an exception to the rule may not be advisable with respect to the Lepidoptera, which are more difficult to be intelligibly described than any other order of insects; while a good figure exhibits to the eye all those markings and shades, that scarcely any description can place clearly before the mind.
When every attempt to investigate the name of your unknown species fails, and you have consequently reason to believe that it is undescribed, the best mode you can pursue for retaining that knowledge of its characters, which from your long investigation you must have acquired, is to note them down in your entomological journal, inserting it under its proper genus with a trivial name of your own. Such a journal you will find almost a sine qua non for containing a catalogue of your insects, and to register any observations concerning individuals you may have had an opportunity of making. With regard to this journal, I should recommend to you to get two blank books. One a duodecimo of 200 or 300 pages, to contain the mere catalogue of your insects, their habitat and localities, or the source from which you derived them. In this you should number the genera in Roman capitals, and the species under each by a figure; leaving considerable space at the end of each genus for the insertion of new species. The other book should be of an octavo size, containing 400 or 500 pages. Under the number of each genus and species you might describe and figure it, if undescribed; if described, note in what it varies from the description, and what characters are overlooked: and in general, insert such observations, with regard to its economy and habits, as you may have had an opportunity of making.--As to foreign insects, wherever you can, upon good authority, be particular in indicating the country and station of each specimen.
I need not say much to you concerning the microscopes you should use for the examination of insects, a common pocket one of three glasses of different powers will answer every ordinary purpose[1591].
* * * * *
We have treated hitherto of insects as we find them now inhabiting our globe: but I must not conclude our correspondence without taking some notice of those that are found in a fossil state. Fossil insects may be divided into those that are found in amber, and those that are found in other substances.
It has been observed with respect to insectiferous amber, that the greater part of the insects found in it exist no longer in the countries that produce that amber, and that in every different locality the insects found in it are different. Thus the amber of Sicily contains various species of Coleoptera not to be met with in other ambers, while that of the Baltic is rich in Diptera and Neuroptera[1592]. It is further observed, that the insects inclosed in the amber of Prussia, and those figured by Sendelius in his Historia Succinorum, all belong to genera at this time found in Europe[1593]. Insects of the following genera are recorded as having been found in this singular substance: Platypus, Elater, Atractocerus; Gryllus, Mantis; larvæ of Lepidoptera; Trichoptera; Ephemera, Perla, Termes; Formica; Tipula, Bibio, Empis; Scolopendra; and various Arachnida[1594]. In a piece of amber in my collection I find Evania, Formica, Chironomus, and some Arachnida.
Fossil insects have also been found in other substances. Parkinson figures larvæ of Libellulina found in limestone[1595]; some Melolonthæ in slate; a Polistes in schistus; Carabi and Necrobia in vegetable debris: but some of these rather belong to a comparatively modern formation[1596].
* * * * *
I observed in the outset of our correspondence, that we were entering an august temple, exhibiting in its inmost sanctuary the symbols of the Divine Presence[1597]. In proportion as we have penetrated, glory from that Shechinah has more and more shone forth: and whether we have considered the uses of insects, their ways and instincts, their forms and structure, and their arrangement in a wondrous and complex system, the WISDOM, POWER and GOODNESS of their and our CREATOR have every where been marvellously conspicuous, and calculated to awaken in us every devotional feeling. If, indeed, we admire and study these little creatures, or any other department of nature, without reference to their CREATOR, and collect and love them merely for themselves, we shall be in some sense idolaters, and, like the ancient world, put the works of GOD in his place. But if, while we admire them and store them up and study them, we see in them his glory reflected, and in the creature love the CREATOR, the study of them, in conjunction with that of the written Word, will be highly beneficial to us, and at the same time that it ministers to our temporal enjoyment will promote our eternal interests.
Taking this view, I cannot better close our correspondence on the subject that has so long occupied us, than in the pious words of one of our most admired poets:
"Happy if full of days--but happier far, If, ere we yet discern life's evening star, Sick of the service of a world that feeds Its patient drudges with dry chaff and weeds, We can escape from custom's idiot sway, To serve the Sovereign we were born t' obey. Then sweet to muse upon his skill display'd (Infinite skill) in all that he has made! To trace, in Nature's most minute design, The signature and stamp of pow'r divine, Contrivance intricate, express'd with ease, Where unassisted sight no beauty sees, The shapely limb and lubricated joint, Within the small dimensions of a point, Muscle and nerve miraculously spun, His mighty work, who speaks and it is done, Th' Invisible in things scarce seen reveal'd, To whom an atom is an ample field: To wonder at a thousand insect forms, These hatch'd, and those resuscitated worms, New life ordain'd and brighter scenes to share, Once prone on earth, now buoyant upon air, Whose shape would make them, had they bulk and size, More hideous foes than fancy can devise; With helmet-heads and dragon-scales adorn'd, The mighty myriads, now securely scorn'd, Would mock the majesty of man's high birth, Despise his bulwarks, and unpeople earth: Then with a glance of fancy to survey, Far as the faculty can stretch away, Ten thousand rivers pour'd at his command From urns that never fail through every land; These like a deluge with impetuous force, Those winding modestly a silent course; The cloud-surmounting alps, the fruitful vales; Seas on which every nation spreads her sails; The sun, a world whence other worlds drink light; The crescent moon, the diadem of night; Stars countless, each in his appointed place, Fast anchor'd in the deep abyss of space:-- At such a sight to catch the poet's flame, And with a rapture like his own exclaim, These are thy glorious works, thou source of good! How dimly seen, how faintly understood! Thine, and upheld by thy paternal care, This universal frame, thus wondrous fair; Thy power divine, and bounty beyond thought, Adored and praised in all that thou hast wrought. Absorb'd in that immensity I see, I shrink abas'd, and yet aspire to thee; Instruct me, guide me to that heavenly day, Thy words, more clearly than thy works, display, That, while thy truths my grosser thoughts refine, I may resemble thee, and call thee mine.[1598]"
FOOTNOTES:
[1582] Compare what is said VOL. I. p. 47--.
[1583] VOL. III. p. 28--. See above, p. 377--.
[1584] See above, p. 546.
[1585] In Elater, Fabricius describes 137 species; in Melolontha, 149; in one section of Rhynchænus, 161; of Curculio, 183; and in his Papiliones Heliconii, 300.
[1586] Thus he places Chlænius holosericæus and nigricornis, which might pass for varieties, far asunder; and Dromius agilis is even put in a different section from D. quadrimaculatus, truncatellus, &c.
[1587] The continuance of this important privilege, by the lamented death of the learned President, is now rendered uncertain; but I trust we may anticipate, that by the liberality of the members of the Linnean Society, and if necessary of the public, this invaluable treasure, by being fixed in the Metropolis, will be more than ever accessible to the British Naturalist.
[1588] It may not be amiss to mention a few:--Sphæridium dytiscoides is a Hydrophilus related to H. fuscipes. S. glabratum is heteromerous, probably one of the Helopii Latr. Carabus retusus and Maderæ both belong to Calosoma. Cistela angustata is a true Choleva. See Linn. Trans. xi. 138.--S.
[1589] See above, p. 406.
[1590] VOL. III. p. 304.
[1591] For dissections the one recommended above, p. 201, may be used. Sometimes a watchmaker's eye-glass, which also sets the hands at liberty, will be found useful.
[1592] N. Dict. d'Hist. Nat. xxxii. 264.
[1593] Ibid. xvi. 281.
[1594] Ibid.
[1595] Organic Remains iii. t. xvii. f. 2.
[1596] Ibid. 281--.
[1597] VOL. I. p. 20.
[1598] Cowper's Retirement.