The art of rearing silk-worms

Preface

In the early part of the present year certain individuals, after a careful investigation of the subject, came to a conclusion that the culture of the Silk-Worm might be carried on successfully in climates of as high northern latitude as that of Great Britain.

These individuals having laid before several persons, distinguished alike for rank and talent, the arguments upon which their conclusions were founded, and having met with a favourable reception, presented a petition to His Majesty, praying that a charter might be granted them for the purpose of incorporating a company, with the power of raising such capital as might be deemed necessary for carrying into execution the cultivation of Silk in Great Britain, Ireland, and the colonies.

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IV

PREFACE.

This prayer His Majesty’s government were pleased to accede to ; and one of the first acts of the company has been, to publish the following translation of the late Count Dandolo’s Essay on the Cultivation of the Silk-Worm ; a work universally acknowledged to stand unrivalled, as at once combining theory with practice.

The mass of argument and facts which it will be found to contain, are, perhaps, amply sufficient to justify the most sanguine expectations of the success of the scheme, if judiciously prosecuted. As, however, that work was peculiarly addressed to climates wherein this culture is known to have flourished for a long period, a few pages will not be misapplied in putting the reader in possession of several other accredited facts, which bear strongly upon the merits of the plan, but which, from its nature, the following work cannot be expected to embrace.

The success of rearing Silk-Worms in any country depends on two circumstances, the healthy state of the insect

PREFACE.

V itself, and a sufficient supply of food for its subsistence.

There is scarcely an individual into whose hands this book may fall, who has not, either in his own person or that of his connexions, witnessed how successfully these insects may be reared on a small scale. In the hands of some this culture has been carried to a considerable extent. Success, therefore, might fairly be looked for as undoubted, were it not that every attempt hitherto made in this country on a scale of magnitude sufficiently large for the purposes of commerce has failed, though it is an incontrovertible fact, that were all the Silk annually grown with success by individuals for amusement collected, it would form no inconsiderable quantity.

To what fatality can we attribute such an apparent paradox, as that a few hundred worms shall succeed, while a few thousand shall as constantly fail, but to our total inattention to, and ignorance of, their habits, rather than to the inaptitude of our climate.

VI

PREFACE.

On reflection, we shall perceive that the power inherent in every animal, of destroying a certain portion of air, and rendering it unfit for the purposes of vitality, becomes dangerous, in proportion as the space in which the animal exists is diminished. A few hundred Silk-Worms, reared in an ordinary room of eight or ten feet square, where the air has free egress and ingress, possess not the power of vitiating the surrounding atmosphere so rapidly, as the current carries off the air so vitiated, and supplies its place with purer.

Provided, therefore, attention be paid to the temperature, and proper food administered, success under such conditions is inevitable. But if the number be increased to several thousands, the quantity of air vitiated in a given time will increase in an equal proportion, and as the current of air receives little or no accession of velocity, it will easily be conceived that unless recourse be had to artificial ventilation, these worms so reared will be coeteris paribus, under circumstances far less favourable than the former.

PREFACE.

Vll

The chances of failure increase, in fact, in proportion to the number of worms reared in any one place; and though a freer ventilation be created, the cold thus necessarily produced will be, if not guarded against, productive in this climate of little less danger than the want of it. Hence the ill success that has hitherto accompanied attempts to rear the Silk- Worm on an extended scale.

In Italy the practice of distributing the eggs intended to produce a certain quantity of Silk, amongst the several tenantry of a proprietor, has greatly diminished the ill effects arising from improper ventilation ; and the temperature of the climate is such as, generally speaking, to put the fear of cold out of the question. But even in that country, until within the last few years, it was a general and well-received opinion, that the mortality among a large number of worms was far greater in proportion than among a smaller quantity.

The cause of this circumstance the following work will be found to investigate vm

PREFACE.

very fully; and they who follow the principles there laid down, need no longer fear such a consequence.

It is not the province of these remarks to investigate the mode of avoiding the evils above described ; the necessary measures are amply pointed out in the body of the work. It will not, however, be useless to beg those readers, who may desire a fuller insight into this interesting subject, to bear ever in mind, that the Silk-Worm is an exotic, to whose health the torrid summers of Italy are no less prejudicial, than the cold climate of the north.

In its native regions it passes its short existence on the branches of those trees that furnish its food, exposed to the warm breezes of an eastern climate, which supporting its life, at the same time carry off those pestilential vapours, that are liable to collect around it in situations more confined. A system of management, therefore, which may as nearly as possible assimilate our own to that climate, and which may have the effect of placing, as

PREFACE.

IX far as is in the power of imitation, these insects in such a situation, must be the most successful, whatever be the latitude in which they happen to be.

Fortunately our hopes of success depend not alone on either the truth or fallacy of mere argument ; we are in possession of facts that equally corroborate our anticipations of success.

In Russia the cultivation of this branch of commerce has been established for several years in a latitude as far north as 54°, and with such success as to warrant the establishment of manufactories for working* the native silk, and the hope that a few years will render that country independent of Persia for the supply of this valuable produce.

In Germany and Bavaria it has likewise succeeded.

Some years back, silk was grown in Prussia, of a quality which was considered superior to that even of Italy ; a fact that gives strength to an observation contained in a paragraph in the Stockholme Journall for March, 1824, and reprinted in

X

PREFACE.

the Bulletin Universalle of April, 1825. After detailing the introduction of several plants lately raised in Sweden, it adds, “ That “ similar motives have instigated the en- “ couragement of the growth of silk in this “ country ; the idea, indeed, is not new, “ and experiments made long ago pre- “ sented encouraging results, though it “ appears that until the present moment “ the attempt has never been seriously “ made. Experiments made during the “ last year (1823) in Stockholm, for the “ purpose of discovering some indigenous “ tree capable of nourishing the Silk- “ Worm, have procured silk of very fine “ quality. The culture of the mulberry- “ tree is extending itself in the provinces “ and important communications on the “ most convenient mode of rearing the “ worm have been generally promulgated. “ The silk so produced in Sweden has “ confirmed, in the amplest manner, the “ remark formerly made on the superior “ fineness and solidity of silk grown in “ the north, compared with that from* “ more temperate climes ; a fact that has

PREFACE.

SI

“ received the unanimous sanction of the “ members of the Royal Society of Com- “ merce, as well as of many silk manufac- “ turers. It supports the ordinary prepa- “ ration and dye equally with the best “ Indian silk, possessing the same bril- “ liancy and the same softness. The silk “ also that has been grown for the last few “ years in Bavaria, is superior to that pro- “ duced in Italy.”

It is true enough, that experiments, even within the present year, have been tried; some with utter failure, others with considerable success; but none of them in buildings properly adapted to secure equal warmth and ventilation ; and it is satisfactory, from the great authority of this book, to collect that experiments so tried, and failing, must have equally failed, had they been tried in the same manner in any climate, or in any country of the world.

The second question, whether a sufficiency of food can be procured in northern climates, and with sufficient certainty, is in a great measure answered by the fore-

Xll

PREFACE.

going statements ; but every doubt on that head must cease, when it is known that though hitherto the white mulberry (for to that alone can we look as a profitable food for this animal) has not been an object of attention, yet it has been grown in almost every part of England with success. At this moment, in the very precincts of London, a plantation of several thousands of these trees is in existence ; some of them not less than fifteen years of age, which, in spite of a soil, perhaps the most uncongenial that could have been selected, are flourishing, and have furnished leaves this present year, for the prosecution of experiments on a scale of some extent.

These trees have been purchased by the British, Irish, and Colonial Silk Company, and will, in the course of the ensuing autumn, be removed to a better soil.

During the last century, some French refugees, in the south of Ireland, made considerable plantations of this tree, and had begun the cultivation of silk with every appearance of the most perfect success;

PREFACE.

XM1 their subsequent removal, however, caused this important opportunity to be neglected, and though the trees are said to have been very flourishing, they have since been entirely cut down. Such facts, however, leave no doubt but that our climate is perfectly congenial to the white mulberry, if cultivated with even moderate attention.

A few words on the expedience of encouraging this new branch of agriculture. Setting aside all that might very reasonably be argued from the increasing consequence of the silk trade, and the disadvantage of being wholly dependant on foreign supplies, let us turn our attention to Ireland, which, from many circumstances, appears peculiarly favourable to such an undertaking.

The climate of Ireland is temperate ; the Irish are an agricultural people, and much of the purposed plan is strictly agricultural. One of the objections raised to its success has been the value of labour. In Ireland labour is lower than on the continent, consequently, were this ob-

XIV preface.

jection ever so solid, there it cannot exist. Ireland possesses an enormous population of women and children ; it is they who must perform those delicate operations of reeling, which the more clumsy hands of the other sex are incapable of performing.

The Irish proprietor must then, and does, view this attempt with the most intense interest, — must wish the fullest success to the objects of the company ; nor is it out of his power to aid them. Let each proprietor, following the example of the noble and distinguished Irish characters who patronise this company, devote some part of his estate to the cultivation of the white mulberry-tree, and let him feel assured that by so doing he is conferring on his country a source of inexhaustible future comfort and prosperity. But at the same time let not the proprietor of this country remain idle, and permit the sister isle to reap the entire benefit of so rich a mine ; let him recollect that, in whatever part of the united kingdom the cultivation of silk shall be established, that there the manufactures dependant on it must follow.

PREFACE.

XV

Impressed with these ideas, the British, Irish and Colonial Silk Company have already directed their attention to the formation of extensive plantations in England and Ireland ; but fully aware themselves how greatly the success of an undertaking of such magnitude depends upon the concurrent efforts of the community at large, they desire to impress on all who can appreciate so desirable an event as the successful cultivation of silk in this country, how necessary to these efforts is their support ; and considering that there is not any mode better calculated to further this object, than to spread widely a knowledge of the principles of an art so little understood, they have caused to be published this translation of a work by the late Count Dandolo, an Italian cultivator, patriot, and scavant, whose meritorious efforts for the improvement of his country have raised his name to a high station in the annals of agriculture.

*

INCORPORATED BY CHARTER.

THE

BRITISH, IRISH, AND COLONIAL

SILK COMPANY,

Capital £1,000,000 — In Shares of £50.

Honorary Members.

Patrons .

The Marquess of Lansdowne. The Earl of Liverpool, K.G.

President.

The Right Hon. William Huskisson, M.P.

Vice-Presidents.

The Marquess of Salisbury.

The Marquess of Downshire.

The Earl of Carrick.

The Earl of Kingston.

The Earl Grey.

The Attorney-General, M.P.

The Attorney-General for Ireland, M.P. Sir John Newport, Bart., M.P.

Sir Thomas L). Ackland, Bart., M.P.

Sir Robert Wilson, M.P.

Col. Bagwell, M.P.

Henry Brougham, Esq., M.P.

Charles Rose Ellis, Esq., M.P.

Edward Ellice, Esq., M.P.

Pascoe Grenfell, Esq., M.P.

Wilmot Horton, Esq., M.P.

T. A. Knight, Esq., F.ll. & L.S.

E. I. Littleton, Esq., M.P.

Frankland Lewis, Esq., M.P.

W. Woolrich Whitmore, Esq., M . P.

Members of the Corporation.

Directors.

Alexander Baring, Esq., M.P.

George Harrison, Esq.

William Manning, Esq., M.P.

N. M. Rothschild, Esq.

Sir R. T. Farquhar, Bart., M.P, Richard Badnall, Jun., Esq.

Cornelius Buller, Esq.

Richard Hart Davis, Esq., M.P.

Welbore Ellis, Esq.

Samuel Hibbert, Esq.

William Holmes, Esq., M.P.

Moses Montefiore, Esq.

John Plummer, Esq., M.P.

Auditors.

William Hill, Esq.

William Howard, Esq.

Officers of the Cortoration.

Bankers.

William Harrison,' Esq.

Solicitors.

Law Agent in Dublin.

John Tew Armstrong, Esq.

Honorary Superintendent.

Arthur Aikin, Esq., S.S.A., F.L.S.

Architect and Surveyor.

Thomas Allason, Esq.

Secretary.

Chapter I. Page

Of Caterpillars in general, amongst which is comprised the Silk-Worm ....... 1

1. General and distinguishing Characteristics of Caterpillars 3

2. Transitions which Caterpillars undergo ... 5

3. Of the Manner in which Caterpillars live, feed, and

exist 8

4. Of the Passage from the Caterpillar State to that

of apparent Death or Chrysalis . . . .11

5. Change of the Chrysalis into a perfect Animal or Moth ; Production of the impregnated Eggs ; Death

of the Moth 15

6. Of the Means by which Nature incessantly tends to destroy an immense Number of Caterpillars, that their excessive Augmentation may not pass the prescribed Limits which it has appointed ; of the artificial Means

by which they may be destroyed . . . . 1(>

Chapter IV. Page

Of the Preliminary Care necessary for the Hatching of the Silk- Worms ...... 34

1. Preliminary Preparation of the Eggs of the Silk-

Worms 37

2. Necessity of having Thermometers to fix the Temperature requisite for Hatching and Rearing Silk- Worms 41

3. Of the Stove-room in which the Eggs must be put to

Hatch 44

4. Hatching of the Silk-Worm 49

Chapter V

Of the small Laboratory into which the New-hatched Silk-fTorms must be put; of their Removal, and Proportion between the IP eight of the Egg and the New-hatched Worm 56

1. Of the Small Laboratory destined to receive the New

Hatched Worm ....... 57

2. Of the Removal of the New Hatched Silk-Worms

into the Small Laboratory, or elsewhere . . .60

3. Of the Weight the Eggs lose before the Worms are

Hatched 72

Chapter VI. Of Rearing Silk-Worms in the Four First Ages . 75

1. Of Rearing Silk-Worms in the First Age . . 67

2. Rearing Silk-Worms in the Second Age . . 94

3. Rearing Silk- Worms in the Third Age . . . 105

4. Rearing Silk-Worms in the Fourth Age . .114

CONTENTS.

XXI

Chapter VII. Page

Of Rearing S ilk- Worms during the First Period of the Fifth Age, until they prepare to rise on the Hedge or Espalier ........ 126

1. Necessity of the Barometer to ascertain the Degree

of Moisture in the Atmosphere .... 134

2. Of the Fumigating Bottle for Purifying the Air of

the Laboratory . . . . . . .140

3. Of the Means of Easily Drying the Mulberry-leaves

even in uninterrupted Rain 150

4. Of Rearing Silk-Worms until the period of complete

Chapter VIII

Of Reariny Silk- [Forms in the Last Period of the Fifth Age, until the Completion of the Cocoon. Observations on the Subject ..... 171

1. Perfect Completion and Maturity of the Silk- Worms ......... 174

2. First Preparation to form the Hedges . . . 175

3. Last Meal given to the Silk-Worms . . . 178

4. Cleaning of the Wicker Hurdles. Finishing of the

Hedges on which the Worms are to Rise . . . 179

5. Separation of the Worms that will not Rise. Last Cleansing of the Wicker Hurdle .... 184

6. Care of the Laboratory until the Silk-Worms have

accomplished the Fifth Age 187

7. Quantity of excremental Steam and Gaseous Substances discharged by the W orms, from the moment of their highest Perfection and utmost Growth, until

the Completion of the Cocoon ..... 195 xxn

CONTENTS.

Chapter IX. Page

Of the Sixth Age of the Silk- Worm, or Chrysalis; Gathering, Preservation, and Diminution in the Weight of the Cocoons ..... 198

1. Gathering the Cocoon 199

2. Choice of the Cocoon for the production of the Eggs

or Seed . 204

3. Preservation of the Cocoon intended for Seed . 210

4. Daily loss in the Weight of the Cocoon, from its First

Formation, till the appearance of the Moth . . 212

Chapter X

Of the Seventh Aye of the Silk-Worm; of the Appearance and Coupling of the Moths ; of the Laying and Preservation of the Eggs . . . 215

1. Appearance of the Moths ; their Coupling . . 219

2. Separation of the Moths ; Laying of the Eggs . 226

3. Preservation of the Eggs 234

. Chapter XI.

Observations on the Varieties of Silk-Worms, and the Essential Differences existing between the Leaf of the Grafted Mulberry-tree and Wild Midberry -leaf, when given to Silk- Worms of One Quality . . 237

1. Of the Silk-Worms of Three Casts or Moultings . 239

2. Of the Large Silk- Worms of Four Casts . • 241

3. Of the Silk-Worms producing White Silk . . 242

4. Of the Common Silk-Worm of Four Casts . . 2-13

5. Comparison of the Leaf of the Grafted Mulberry, and

that of the Wild Mulberry, when given to Silk- Worms of One Quality ..... 244

CONTENTS.

Chapter XII. Page

Of the Diseases of Silk- [Forms in their different Ages, the Causes which produce them, and the Means of preventing them ....... 250

1. Disease proceeding from the Imperfection of the

Eggs 252

2. Disease attacking the Silk-worms, when the Rules I

have prescribed for their Hatching have not been strictly followed up, although the Eggs were Good and well Preserved. 254

3. Of the Diseases incident to Silk-Worms in the Four First Ages, by 111 Management .... 256

4. Serious Diseases occasioned by 111 Management in

the Fifth Age of the Silk-worm . . . .261

Chapter XIII

Of the Buildings and Utensils necessary to the Cultivation and Rearing of Silk- [Forms . . . 2S4

1. Of the Proprietor’s Laboratory .... 287

2. Of the Cultivator or Tenant’s Laboratory . . 302

3. Of the Space destined for Keeping and Preserving

the Mulberry-leaves Fresh and Good . . . 307

4. Of the Utensils necessary to the Art of Rearing and

Cultivating Silk-Worms , 309

Chapter XIV

General View of all the Facts stated in this [Fork immediately connected with the Art of Cultivating

S ilk- [Forms 315

1. Facts relative to the Space which Silk-Worms should

occupy before, and at the time of Hatching . . 317

2. Facts relative to the Space which Silk-Worms should occupy during their different Ages .... 319

XXIV

CONTENTS.

Page.

3. Facts relative to the Quantity of Leaves consumed by the Silk-Worms during- their different Ages ; Observations on the Subject ..... 320

4. Facts relative to the Increase and Decrease of the

Silk- Worms in Size and Weight .... 326

5. Facts relative to the Cocoons that contain the Living, Diseased, or Dead Chrysalides .... 327

6. Facts relative to the Production of the Eggs . . 338

7. Facts relative to the Buildings and Utensils . . 339

Chapter XV

Of the Advantages which the Country, the Proprietors, and Cultivators, must derive from the Improvement of the Ordinary Method of Rearing Silk-Worms . 340

1. Annual Value of the Production of the Cocoons, or of the Silk they yield when Exported. Some Views of the Value of the Manufactured Produce which can be Exported 343

Appendix

2. Annual Profit which the Proprietors and Culti-

vators may derive from Rearing Silk-Worms, in cases when the Proprietors furnish the Leaves, and the Cultivators supply the Labour, and they divide the Cocoons between them 319

3. Net Profit which those may Clear who Rear Silk-

worms entirely on their own Account, either Employing their own Mulberry-leaves, or Purchasing the Leaves 338

4. Annual Increase of Riches which the First General

Improvements in the Cultivation of Silk-Worms would Introduce into the Nation, by the adoption of the Method I recommend 362

List of Plates . . 367

THE

ART OF REARING SILK-WORMS.

Chapter I. Of Caterpillars Generally, Amongst Which Is Comprised The Silk-worm

He who contemplates nature finds an inexhaustible source of wonder and pleasure in considering, among the class of insects, their forms, their colours, the different offensive and defensive weapons with which they are provided, their curious habitudes, the bond of union which is shewn in some kinds, and the prudence and industry which they employ, less indeed for their individual preservation than with a view to secure the perpetuity of the'species, while yielding to the soft and powerful impulse of nature. But if this innumerable family of little animals furnishes ample matter for the curious researches of the naturalist, it affords also a subject of meditation for public

B economy, since some kinds of these beings cause even national calamities, while on the contrary other species greatly contribute to the prosperity of states and individuals. It would be too long, and not necessary to the purpose I have in view, to enumerate here each family of insects : I shall confine myself to observe that those kinds which have wings present themselves to us under different states, in the various periods of their lives, and that the faculty of reproducing their species is reserved particularly for the last period. Thus one sees that, while the butterfly deposits its eggs, which are impregnated soon after copulation, these eggs do not immediately produce other butterflies, but, on the contrary, little animals of a long cylindrical form, composed of a certain quantity of segments or rings, having below a certain number of feet, of various forms and substances, with other particularities which I shall describe afterwards. Such, in general, are caterpillars, amongst which the silk-worm occupies the first place, and will form the subject of the following treatise.

In this first Chapter I shall make some observations,

1st, On the external and general characters of caterpillars.

2d, On the changes they undergo.

3d, On their manner of living, their growth, and preservation.

SILK-WORMS.

4th, On their transition from the state of caterpillar to that of apparent death, or chrysalis.

5th, On the change of the chrysalis into a perfect animal, or butterfly ; on the laying of the impregnated eggs, and on the death of the butterfly.

6th, On the method adopted by nature to destroy a great number of them, that they might not exceed the limits fixed for them, and on the means which man may employ with the same object in view..

ls£. On the General and External Characters of Caterpillars .

Caterpillars have, as I have observed, a long body, more or less cylindrical, which is formed in its length of twelve membranous parallel rings, which, in the movements of the animal, mutually contract and elongate. They have uniformly a scaly head, of a substance similar to horn, provided with two very strong jaws, formed like a saw, which are moved horizontally, and not from above downwards, as among animals with red blood. Under the jaws is placed the contrivance by which each caterpillar deposits the silky substance. They have never fewer than eight feet, and never more than sixteen ; the six first, formed of a scaly substance similar to that of the head, are fixed under the three first rings, and can neither

B 2 be sensibly shortened or lengthened ; the others, whether two, four, six, eight, or ten in number, are membranous, flexible, and attached in pairs to the back part of the body, under their corresponding rings.

These last legs are those which transport the animal ; they are provided with little hooks, tolerably strong, calculated to give him support, and enable him to climb. All the hinder legs disappear, of whatever kind the caterpillar may be, when it changes into a butterfly, and there remain only the six first, which are variously •modified. The anus is placed under the last ring. Caterpillars breathe by eighteen apertures, situated nine on each side of the body, through which the air passes in and out. Each of these openings is considered as the termination of a particular windpipe. A great number of caterpillars have eyes ; some of them are utterly blind, but they acquire the power of vision when they attain the state of butterflies. Having pointed out the general external characters which distinguish caterpillars from all other animals, it would seem useless to mention that some, according to their different kind, are large, middling, and small; but however they are all very large, compared with the egg from which they are produced, or with themselves at the moment they emerge from the egg, as will be seen in Chapter VII.

SILK-WORMS.

Some caterpillars have a smooth skin, as the silk-worm, others are rough, and elevated in certain parts ; some have one either partially or entirely of velvet, covered with hair or bristles, of various colours, often so beautiful, lively, and so well shaded, that art cannot imitate them. It is not a part of my subject to speak of the anatomical structure of these insects.

2. Of the Changes which Caterpillars undergo. A character peculiar to caterpillars is to change their skin at least three times before they reach the period when they spin the silk which they contain, in order to assume the chrysalis state in the cocoon or envelope which they have formed (§ 4.)

In the greatest number of caterpillars this change takes place three or four times, in others from five to nine times. These changes are called casting of the skins, and are in fact diseases that often destroy the lives of a great number of these insects (§ 6.)

One single skin allotted to an animal which, in a short space, increases its weight a thousand times, would with difficulty have been able to distend itself sufficiently to cover it entirely. Thus provident nature has extended over the body of the caterpillar the embryos of the skin of each moulting, which supply also the hairs or bristles with which many kinds are abundantly covered

As the animal increases more than the skin admits of distension, this falls off and is replaced by a second which is softer ; this again is detached in the same manner as the first, and is followed by a third, a fourth, and so on.

The slough of caterpillars is an entire covering applied to all the exterior parts of the animal, in which you recognise the hairs, the feet, the head, the skull, the jaws, teeth, 8fC.

As soon as the skin begins to pinch the caterpillar, it immediately abstains more or less from food, which circumstance points out with certainty the disease occasioned by casting of the skin. This is the reason also why the caterpillar becomes much less as the time of changing its skin approaches.

Then it throws out at different points of its body silky traces, which it attaches to neighbouring bodies, in order that, while it exerts itself, the skin which covers it may remain fixed in the spot where it is placed. When this operation is finished the animal remains more or less quiet, and afterwards generally begins to move its head, turning itself about. Thus, the mask or scale which covers its snout being pushed forwards by the new skin formed underneath, is the first portion detached.

The mask being detached, the caterpillar pushes forwards, with effort, through the opening of the

SILK-WORMS.

first ring, which is smaller than those which follow ; and as it has already fastened the skin by different threads, and particularly by the hooks of the two processes of the anus, which it has already attached where it is, it is not difficult to free its two first feet, and afterwards to escape in a short time from its envelope, by the help of its vermicular movements.

Sometimes the covering is broken, or a part remains attached to the extremity of the caterpillar, which cannot always get rid of it. Then it swells or enlarges in the part which is disentangled, while the envelope compresses the rest of the body : in such cases the animal dies, after a greater or less exertion .