Elements of entomology: an outline of the natural history and classification of British insects

Preface

Amongst the numerous works published on Entomology, it appeared to the author that there was none which gave, in a popular and readable form, an outline of the principal groups into which Insects are usuallydivided. It was with the object of filling up this gap in our Entomological literature that the present little book was written.

The plan which the author laid down for himself at starting, and to which he has endeavoured to adhere closely throughout, consisted in passing lightly over the surface of the subject, avoiding details as much as was consistent with giving a true picture of the principal phenomena of Insect life ; and with the view of bringing the subject home to his readers as closely as possible, he has always endeavoured to select, as examples of each group, those common insects which occur almost everywhere. In some cases possibly he may have referred to species which are less abundant, but for one instance in which this has happened, he might cite many in which he has

VI

PREFACE.

successfully resisted the temptation of describing the habits of rare hut highly interesting insects. The descriptions are not drawn up with scientific detail, but at the same time it is hoped that by means of these, coupled with the accounts given of the habits of the Insects, the reader may be able to determine all the species described in the following pages.

As the hook is intended solely as a guide for the beginner in his first steps, the author has taken it for granted that his readers on commencing its perusal will know nothing of the subject on which it treats, and he has accordingly prefaced the descriptions of the different groups of Insects and of the habits of their members, with a general account of the structure and vital phenomena of these interesting animals. Throughout the work he has endeavoured to combine simplicity of language with scientific accuracy, in the hope that his labours may be instrumental in fostering a taste for the delightful science of Entomology, especially in the minds of the rising generation.

Contents

CHAPTER Page

I. What is an Insect P 1

II. Of the Structure of Insects in general 6

Chapter I. What Is An Insect ?

The question with which this Chapter is headed may appear supererogatory to many, hut it is nevertheless one the solution of which is necessary before we can proceed further. The popular notion of what is meant by the term * insect ’ is rather too vague to be of much service in a scientific point of view, — it is capable of being stretched to almost any extent, so as to include creatures of the most dissimilar nature, when there is any occasion to bring them under a common denomination. Thus even in works professing to initiate their readers into the mysteries of nature, the term insect may be seen applied indiscriminately to Leeches, Snails, Limpets, and invertebrated animals of almost all kinds ; and nothing is more common than to see the name of coral-insects given to the polype-architects of those wonderful structures, which, in the tropical regions of the Pacific, serve as the foundation and protection of multitudes of fertile islands teeming with a happy population. More-

DEFINITION OF AN INSECT.

over there are many animals which, in the phrase of naturalists, are nearly allied to the creatures whose history we propose to trace in the following pages ; that is to say, which agree with them in the principal outlines of their structure, but which, from characters of more or less importance, are separated from the true Insects by the zoologist. These, although often denominated insects in common parlance , form no portion of our present subject, so that, to avoid confusion, it will be necessary to settle the boundaries of these neighbouring groups, in order that the reader may know exactly the nature of the entertainment to which he is invited.

Our bill of fare will consist exclusively of insects ; but, what is an Insect ? An Insect may be defined as an air-breathing articulated animal, with its body divided into three distinct regions, with a pair of jointed organs on its head, and with six legs. But there are two objections to this definition in the present case; in the first place, it does not apply without exception to all the animals included in the class of Insects; and in the second, if it did, it is totally unintelligible to the beginner. The exceptions, however, are so few in number, that they may be disregarded for the present, and if the second objection can be got rid of by a little explanation, the above definition will serve to give us a sufficiently accurate idea of what is and what is not an Insect.

An articulated animal is one, the surface of whose body exhibits a division into a number of rings, or segments, and this character is very distinctly possessed by insects. Of these segments the number varies greatly in different groups of articulated animals, but in Insects it is pretty uniformly thirteen.

DEFINITION OF AN INSECT.

In these creatures, the different structure of the segments in different parts of the body enables the latter to he divided into three regions as they are called ; one segment forming the head or first region, three going to form the second region or thorax , and nine the third or abdomen. The head is furnished with a pair of jointed organs very variable in length, and often exceedingly curious in their form, which are called the antennae ; and each segment of which the thorax is composed bears a pair of jointed legs. An animal presenting these characters may be safely pronounced to be an insect.

But “ to make assurance sure,” it may not be amiss to give a slight sketch of the most prominent characters of the groups which have been already alluded to as nearly allied to our little favourites. Not only are these commonly regarded as insects by the unlearned, but the great Linnseus, the Father of Modern Natural History, included them all in his great class of Insects, which, in fact, represents exactly the group of articulated animals with limbs” ( Arthropoda ) admitted by all modern zoologists. But although, according to the light which existed in the days of Linnaeus, these creatures might well be placed together in a single class, the researches of his successors soon showed that they presented characters of sufficient importance to justify their being divided into several classes, and in the present day the existence of four such groups is generally admitted. Of these the Insects form one, and the distinctive marks of the other three may be given in few words.

The nearest approach to the Insects is made by the Myriapoda *, of which the common Centipedes are * Gr. murias, a myriad, and pous, a foot.

B 2

CLASSES OF ARTICULATED ANIMALS.

well-known examples. In these the body is elongated and composed of numerous similar segments, each of which bears at least one pair of feet ; the head, as in the Insects, bears a pair of antennse, and the creatures breathe air. The Spiders, whose ingenuity in weaving, and supposed malignity, have alternately been the objects of admiration and dread from time immemorial, together with the Scorpions, those terrible inhabitants of tropical lands, and some other creatures, form the class of Arachnida*, in which the body is never composed of more than two regions, the head and thorax being completely united and bearing four pairs of legs. Like the Insects, these creatures also breathe air. Of the fourth class, the more prominent members would fall, in a popular classification, under that most miscellaneous denomination of Shellfish ; it includes alike the lordly Lobster and the delicate Prawn, the humble Crab and the “fine brown Shrimp,” the delight of Gravesend holiday folks. This group, to which the name of Crustacea *j* is given, is distinguished from all the rest by its adaptation to an aquatic life; its members breathe by means of gills, which require the constant contact of moisture to keep them in working order. The structure of the body exhibits great differences in different groups of Crustacea, but some of the segments of all parts of the body usually bear jointed organs more or less resembling legs.

The above characters, meagre as they are, will suffice to show the principal differences between Insects and the three classes of animals most nearly related to them ; it will therefore be unnecessary to inquire any further into the distinctive characters * Gr. arachne, a spider. + Lat. crusta, a crust.

CLASSES OF ARTICULATED ANIMALS.

of the latter. With regard to the Insects, however, the case is very different, and it will be quite impossible to render our sketch of the History of British Insects intelligible to the student, without a short account of the general phenomena of insect life. This will be given, as briefly as possible, in the two following chapters.

Chapter II. Of The Structure Of Insects In General

In Natural History, as in most other sciences, the old adage, that there is no rule without an exception, finds many applications, so that it is frequently difficult, or almost impossible, to give unexceptionable characters for any particular group of animals. Thus even the very short definition of an insect given in the preceding chapter was not free from exceptions ; but nevertheless, by far the greatest number of these creatures present a very close resemblance in their general structure ; and indeed the wonderful variety which they apparently present, is produced entirely by the modifications which the same elements undergo, to fit these little creatures for the varied and important parts assigned to them in the (economy of nature. The object of the present Chapter is to give an account of these general points of resemblance, with reference only to such of their modifications as are necessary for the proper understanding of the subject.

External Skeleton. — In most of the articulated animals, and especially in those provided with legs, the segments of the body are formed of firm rings, united with each other by a softer skin, by the aid of which the hard case of the body acquires a greater or less degree of flexibility. In some of these creatures, such

EXTERNAL SKELETON.

as the ordinary Crustacea, this hardness is obtained by the deposition of calcareous matter, principally carbonate of lime (or chalk) , in the skin ; but in the rest it is produced simply by a thickening of the skin in those particular parts, leaving the intervening portions soft and flexible. Thus the body of an articulated animal may be regarded as a jointed tube ; and as the skin of the limbs and other appendages is also hardened in the same or even a greater proportion, the whole skin of the creature forms a sort of case within which all the soft parts are securely

sheltered. To this firm The external skeleton of skin are attached the muscles, by which the movements of the differentparts are effected; and as these act upon their points of support in exactly the same way that the muscles of man do upon the hones of his skeleton, the hardened covering of these animals has been denominated their skeleton ; hut with this difference, that whilst in the

Insect.

a. The head, with the eyes, the bases of the antenrue, and the palpi, b. The prothorax, with the first pair of legs. e. The mesothorax, with the second pair of legs, and the bases of the first pair of wings. d. The metathorax, with the third pair of legs, and the bases of the second pair of wings, e. The femur or thigh. /. The tibia or shank, g. The tarsus, h. The abdomen, i. The ovipositor.

EXTERNAL SKELETON.

former case the muscles lie upon the outside of the bones upon which they act, in the latter they are entirely enclosed within the firm tubes which furnish them with points of attachment. Hence the term external skeleton has been applied to the integument of the Insects and their allies.

In most insects this well deserves the name of skeleton, being usually of a horny texture ; but in some it is comparatively soft, although even in these the division of the body into segments is distinctly perceptible, and the tubes of which the limbs are formed exhibit a greater degree of firmness than the rest of the body. As all the more important characters of the different orders of Insects are derived from the peculiarities of this external skeleton, it will be necessary to describe its structure at some length. It is usually composed, as already stated, of thirteen segments ; but of these some are often united together in such a way as to form but a single piece, whilst others are sometimes reduced in size and concealed within their neighbours.

The Head. — The first segment forms the head. It consists of a single piece having an opening in front or beneath for the mouth, and another behind for the passage of the oesophagus into the body. On its surface it exhibits the eyes, and gives attachment to a pair of jointed organs called antennae.

The mouth in Insects is furnished with a variety of organs to enable them to take their nourishment, and as this is exceedingly various, the structure of this part appears so different in the different groups of these creatures to suit them for the particular offices assigned to them in the oeconomy of nature, that its peculiarities furnish us with some of the most import-

THE MOUTH.

ant characters for the classification of the innumerable beings belonging to this class. Thus in some cases the mouth is adapted for biting solid substances, the different organs of which it is composed being modified in their form according to the nature of the bodies upon which they are to be exercised ; — in others, the nutriment is taken entirely in a fluid form, and the mouth is arranged accordingly, so as to furnish an apparatus for suction, at the same time that, when necessary, some parts of it are adapted to the production of wounds in the tissues of plants and animals upon whose fluids the creatures feed; but notwithstanding this diversity of function, it is remarkable that in all these animals the fundamental structure of the mouth is essentially the same, and the investigations of comparative anatomists have proved, that, however dissimilar they may appear, the organs forming the mouth are identical in all insects.

In the mouth of an ordinary biting insect these organs are as follows. The aperture of the mouth is bounded in front by a small horny plate, which is moveably articulated to the lower part of the front of the head (called the clypeus ) . This is the labrum or upper lip ; it varies greatly in size and form, and its peculiarities often furnish characters of importance for the distinction of different groups. Immediately below this is a pair of horny jaws, each composed of a single piece, and articulated by a sort of hinge-joint, one on each side of the opening of the mouth. These are called the mandibles ; they are usually strong, curved and pointed, and very commonly armed with teeth on their inner edge, or at the tip. The mandibles form the principal agents in biting , and it is by the aid of these that many insects are enabled to gnaw

b 5

THE BITING MOUTH.

their way through wood and other hard substances ; it is with them also that the predaceous insects seize

Head and mouth of an Insect ( Carabus violaceus).

1. The head, a a. Antennae, b b. Mandibles, c. Maxillae, dd. Maxillary palpi.

e. Labial palpi.

2. The parts of the mouth dissected, a. Labrum. bb. Mandibles, cc. Max-

illae. d. Labium.

and destroy their victims. In the form of these organs, and of the teeth with which they are armed, we have consequently as distinct an indication of the mode of life of these animals, as that furnished by the jaws of any quadruped. In the most carnivorous species we find the mandibles pointed and hooked, and the teeth sharply conical, reminding one, to compare small things with great, of the formidable canine teeth of the Lion or Tiger, which indeed are scarcely so ferocious as these little tyrants; whilst in those which are formed for gnawing hard substances, the tips of the mandibles are flattened so as to furnish a broad cutting surface, the teeth of the inner edge are blunt, and the lowest of them, being tubercular in their form, offer no distant resemblance to the molars of quadrupeds. Between these extremes the man-

THE BITING MOUTH.

dibles present every variety of form to suit them for the almost infinite variety of oflices to which they are applied.

Behind these horny jaws, which often attain most formidable dimensions, and indeed can bite very severely, we find a second pair of jaws, articulated, like the first, to the sides of the mouth, but unlike these composed of several horny pieces. Like the mandibles also they are usually furnished with teeth on the inside, and in many predaceous insects they are curved and acute at the tip. To these jaws the name of maxilla is given. On the outside each maxilla is provided with a jointed organ, called & palpus, which is inserted at the extremity of the third joint of the maxilla. The palpi vary considerably in length, and in the number and form of their joints; they appear to be employed as organs of touch. Within them, in a few insects, there occurs a second palpus, which however is very short, and never composed of more than two joints ; it is regarded as a modified form of a portion of the body of the maxilla, which only makes its appearance as a distinct part in a few groups of insects. The number of palpi, or jointed organs attached to the maxillae [maxillary palpi as they are called), is therefore either two or four. The mouth is closed from beneath by the labium or lower lip, which consists of two parts, namely the mentum , or chin, a broad horny plate of very variable size and form, and the ligula , or tongue, which lies upon the inner surface of this, and is usually a membranous or fleshy organ, although when it projects beyond the mentum, it is generally supported by a horny plate. The labium bears a pair of palpi [labial palpi) , which are usually shorter, and composed of fewer joints than

THE BTTING MOUTH.

tlie maxillary palpi, which however they resemble in other respects. Such is the normal structure of the mouth of an insect.

But it has already been stated that in many insects the mouth is solely adapted for the consumption of fluid nutriment; such are the gay butterflies that flutter in the bright sunshine from one flower to another, — the moths that take their place when the shades of evening cover the earth, — the flies, whose presence in our apartments is so unwelcome, — the gnats that attack us so remorselessly in our evening walks, — and the bug, whose nocturnal inroads have broken the slumber of many a weary traveller. And these are only well-known examples of a host of insects, which all agree in the possession of a suctorial apparatus at the mouth, — a multitude which probably equals in number those in which the organs of the mouth present their regular masticating arrangement. Unfortunately, however, for the brevity of this part of our story, this is the only point in which all these creatures agree ; the animals all live by suction indeed, but how different are the substances upon which they feed, and, as we might expect, how different are the modes in which their structure has been modified by the moulding hand of Nature, to suit each for its peculiar functions ! Few things could furnish the natural theologian with a better proof of design in nature than the investigation of the course adopted in the modification of the same parts, which we have just seen in the form of powerful biting organs, to form the agents of a suctorial existence ; nor is our admiration in any degree lessened by the consideration that many of the creatures in which these pluenomena are to be witnessed are so small as almost to

MOUTH OF THE BEE.

elude the naked eye, for, in the words of the late Professor Forbes, “ wonders are none the less wonderful for being packed into small compass.”

But instead of proceeding at once to consider the structure of the truly suctorial insects, or those in which the whole of the organs of the mouth have been rendered subservient to the imbibition of fluids, it may be as well to stop by the way to examine the construction of these parts in certain insects, which exhibit, as it were, a union of the two characters. Such insects are the well-known Bees, in which this combination of structure is necessary to enable them on the one hand to collect their liquid food from the nectaries of flowers, and on the other to perform those ingenious operations which have rendered them objects of admiration in all ages. The suctorial organ in these insects consists of the tongue, which is drawn out into a long tube ; it is accompanied by the labial palpi, and enclosed in a long sheath composed of the maxillse, which acquire a scaly texture, and overlap each other partially at the edges. The labrum or upper lip still retains its ordinary position at the front of the mouth, and immediately behind it is a pair of strong mandibles, with which the Bees perform the most varied functions, some of them digging deeply into the earth or into posts, others cutting pieces out of leaves as neatly as if they were done with scissors, others again working deftly in clay or mud, whilst the Hive Bee surpasses all the rest in her delicate wax -work.

In the mouth of the Bee there is but little difficulty in recognizing the organs already described as belonging to an ordinary biting insect, and yet many of them are so modified, that on a careless glance their origin

MOUTH OF BUTTERFLIES AND MOTHS.

would appear very doubtful. The principal modifications consist in the elongation of the tongue, and of the labial palpi and maxillae which form its sheath ; and besides these the maxillary palpi are so greatly reduced in size, as to be scarcely perceptible in many cases without a most careful examination. An increase in some parts, and a diminution of others, are therefore the changes for which we must look in our investigation of the truly suctorial mouths. These are of three principal kinds, of each of which examples have been referred to above.

In the Butterflies and Moths the sucking organ consists of a long curled tube, which reposes between a pair of hairy cushions projecting from the front of the head. In this their natural state we should have as great difficulty in discovering the nature of these organs, as in recognizing the features of some well-known friend recently fallen a victim to the fashionable epidemic of hair ; but on getting rid of these obstructions, the difficulties to a great extent vanish. We then find that the hairy cushions are jointed palpi, attached by their bases to a small lower lip, and by a diligent search we may discover the representatives of the mandibles and labrum in the form of three minute processes above the base of the spiral trunk. The latter, which would appear to be the most unaccountable organ of the whole, is really formed out of the two maxillae, the basal portions pf which, although small, exhibit nothing remarkable in their structure, whilst the tips are produced into a pair of long wrinkled tubes. Each of these tubes is furnished along the entire length of its inner surface with a pair of ridges, which fit together exactly, and thus the two maxillae adhere together to form a single organ with

MOUTH OF GNATS AND FLIES.

two tubes. At tbe point where the tubular prolongation springs from the basal portion of the maxilla, there is a very minute two-jointed palpus, which sufficiently indicates the true nature of the organ. The use of this beautiful spiral trunk needs no explanation, for there can be few who have not observed butterflies busily engaged in pushing their unrolled tongues into the recesses of flowers in search of the sweet juices which usually collect there.

Very different from this elegant and harmless organ is the formidable weapon with which the mouths of the Gnats and many flies are armed, and which often causes these insects, contemptible as they are from their size, to rank amongst the greatest pests of the countries where they abound. Beneath the heads of these little creatures we find a tubular organ, which is sometimes fleshy, and sometimes horny in its texture. In either case it is the representative of the lower lip, and its tip is often furnished with a fleshy disc formed of two lobes, which is constantly employed as an organ of touch, and is considered by many entomologists as the representative of the labial palpi. This tube or proboscis is cleft on its upper surface, and within it we find, in the most perfectly organized of- these insects, five bristles or lancet-like organs, some of which can be pushed out of the sheath -like lower lip so as to wound the skin of other animals, when, by the combined action of the whole, a sort of pump is produced, by means of which the blood is sucked up into the body of the insect. Four of these lancets represent the two pairs of jaws of the biting insects, and one pair of them, representing the maxillae, are even furnished with palpi, composed of from one to five joints, which project from the base of

MOUTH OF GNATS AND FLIES.

the sheath ; the fifth represents the tongue ; it is considered to be the principal agent in wounding the victims of these little blood-suckers. Over all these is another piece broader than the rest, — this is the labrnm. This complexity of structure, however, is by no means universal in those insects whose lower lip exhibits the formation above described; in some of them the bristles or lancets are reduced to an exceedingly small size, or altogether wanting ; in others, a single piercer, the tongue, is present, whilst in others the bristles representing the maxillse and mandibles make their appearance together or separately. When the maxillary bristles are deficient, the maxillary palpi are usually found attached to the stalk of the labium.

We have thus disposed of four out of the five examples of suctorial insects to which reference has been made ; the fifth is an insect whose very name is a terror to all good housekeepers. But the common Bug has only been selected as a familiar example of a peculiar structure ; the numerous other insects which partake more or less of its characters, although often distinguished by the same unsavoury qualities which render our domestic species such a very disgusting neighbour, are at all events free from its most disagreeable associations, — they inhabit the fields and woods, and are often of great beauty, a quality for which the common Bug is certainly not remarkable. In these insects we find a horny beak (i rosh'um , or promuscis) of variable length, springing from the under side of the head, and lying folded down beneath the body when in repose. This, on examination, is found to be a tube composed of three or four joints, and open all along its anterior surface ; it is evidently

MOUTH OF THE BUGS.

composed of the labium and its palpi soldered together, and turned inwards so as to form a tube. The sides of the slit above mentioned have a rather wider space between them towards the point where the rostrum springs from the head, and this is closed up by a long, transversely wrinkled organ, the representative of the labrum or upper lip. Within the tube we find four bristles, which, as in the Flies, represent the mandibles and maxillse ; these can be pushed out of the jointed sheath, and as they are sharp at the point, they are employed in piercing the tissues of living plants and animals, upon whose juices these little creatures feed, the solid rostrum at the same time furnishing the support necessary to enable such delicate bristles to penetrate into the firm tissues.

We have thus, as briefly as possible, traced the structure of the mouth in different groups of insects, and indicated the mode in which these apparently dissimilar organs are produced by the modification of the same essential parts. Brief as these observations have been, I am not without some fear that they may be subject to the dreadful imputation of dryness, and if so, my justification must be, that it is quite impossible entirely to avoid this fault, and at the same time to give a clear idea of matters of such pure detail; and in fact the brevity with which the subject has been treated is of itself inimical to that charming lightness with which many popular writers on science dilute their scanty materials. The reader may take it for granted, however, that no knowledge worth having can be got without some little effort, and he will find that by taking the trouble of reading through the preceding observations, his progress through the study of the classification of insects will be mate-