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a branch, ty feeing a quantity of duft continually iffuing out of a hole in the bark. Mr. Reaumur obferved this in the branch of an apple tree in his garden, and tying a bag of linen over the hole, he caught the animal in its winged ftate, and it proved to be a large kind of greyifh phalsena. Three or four other kinds of thefe wood caterpillars have been difco- vered at different times, but it is fo very difficult to find them, or to get at them when found, that probably there are many fpecies of them yet unknown. Reaumur, Hill. Inf. vol. 2. p. I. p. 288.
The root caterpillars, afrd thofe which live within the branches of plants, are much more eafily found out. The roots of fcrophularia, and the ftalks of lettuces, and fomc other plants, afford caterpillars which feem all of the fame fpecies. Thofe found in the lettuces are extremely plentiful fome years, and deftroy vaft quantities of that plant. Thefe ufually have their firft habitation in the flalk, near the root, and they increafe it in fize as they grow and feed. The fkin of this kind is white and tranfparent, but has a few brown fpots ; thefe finally produce a fmall phalama. The fame fpecies is fome- times found in the ftalks of elecampane ; and it is well known that there is another kind which lives always in the heads of the thiftle kinds. Thefe, and a few others, are the known fpecies of this kind ; but as the habitation of all thefe is fo much out of the common road, that nothing but the greateit accidents can difcover it, it is very probable that there yet remain many kinds unknown. The fruits of feveral kinds become alfo the food and lodgement for feveral fpecies of caterpillars ; and it is fmgular among thefe, that they will eat indifferently of feveral kinds of fruit, as pears, plums, apples, and peaches, whereas the generality of the common caterpillars that feed on ■ leaves, are allotted only fomc one peculiar kind, and will ra- ther die than eat of any other, tho' this is not a rule without exception even in them.
Nothing more furprifes us, in regard to infects, than their induftry, and in this the caterpillars yield to no kind ; not to mention their fdk, the fpinning of which is one great proof of it. The fheaths and cafes which fome of thefe infects build for the palling their transformations under, are, by fome, made of the fdk, with their own hair mixed, with pieces of bark, leaves, and other parts of trees, with paper, and other materials, and the ftruclure of thefe is well worthy our atten- tion.
There are others whofe workmanfhip, in this article, far ex- ceeds thefe. There is one which builds in wood, and is able to give its cafe a hardnefs greater than that of the wood itfelf in its natural ftate. This is theftrange horned caterpillar of the willow, which is one of thofe that eat their exuviae. This creature has extremely fharp teeth, and with thefe it cuts the wood into a number of fmall fragments ; thefe fragments it afterwards unites together into a cafe, of what fhape it pleafes, by means of a peculiar lilk, which is no other than a tough and vifcous juice, which hardens as it drys, and is a ftrong and firm cement. This alone, however, would probably not fuffice to give the work a due ftrength and folidity, were it pract ifed on the rough pieces of wood, as they are cut from the tree, becaufe it would only acf. upon the fuperficial part of each piece. In order, therefore, to make it fink into the very fubftance of every fragment, the creature moiftens every one of them, by holding them fucceflively a confiderable time in its mouth. By this means they are penetrated with the fali- val moifture, and their pores give eafy accefs to the vifcous fluid they are afterwards to be impregnated with. The foli- dity of the cafe being thus provided for, we are to confider, that the caterpillar enclofed in it is to become a butterfly, and the wonder is, in what manner a creature of this helplefs kind, which has neither legs to dig, or teeth to gnaw with, is to make its way out of fo firm and ftrong a lodgement as this, in which it is hatched. It has been fuppofed by fome, that the butterfly, as foon as hatched, difcharged a liquor which foftened the vifcous matter that holds the cafe together, and fo its feveral fragments falling to pieces, the way out lies open. This is evidently the truth of the cafe, tho' thofe who fuppofed it, did it by mere conjecture ; for, on a ftridt examination, this liquor is always to be found in the animal, and is of the moft proper kind for fuch a fervice. Reaumur judged, from the effects, that this liquor muft be of a fmgular nature, and very different from the generality of animal fluids ; and on differing this creature in the caterpillar ftate, there will always be found, near the mouth, and under the aefophagus, abladder, of the bignefs of a fmall pea, full of a limpid liquor, of a very quick and penetrating fmell, and which, upon divers trials, proves to be a very powerful acid ; and, among other properties, which it has in common with other acide, it fenfibly foftens the glue of the cafe, on a com- mon application. Phil. Tranf. N°. 469. p. 463. It is evident that this liquor, befide its ufes to the caterpillar, remains with it in the cbryfalis ftate, and is the very tiling that gives it a power of diffolving the ftrufture of the cafe, and making its way through in a proper manner, at the ne- ceffary time. Dr. Boerhaave has adopted the opinion, that there are no true acids in animals, except in the ftomach, or interlines ; but this familiar inftance proves the error of that determination.
Near the head, on the under part of the fird ring of the bodv there is placed a fort of flefhy protuberance, or nipple, vriiile the creature is in the caterpillar ftate. This nipple, in its common ftate, is hid within the flelh, and only appears on preffing the body of the animal. This is not peculiar to this caterpillar, for many other kinds have an organization of this kind, tho' not all. In foine it is fingle, in others double, in fome others divided into three parts, and in this particular in- ftance, into four.
Mr. Reaumur, in the fecond volume of his hiftory of infects^ has given a full account of the changes, and manner of living, of thefe little, and generally efteemed contemptible animals; not any of which may not afford great fubject of admiration in the mind of a curious enquirer into the works of nature; but, among the great number he has there defcribed, there are fome which appear fo very fmgular, as to call for a more than ordinary attention. Of thefe, one very remarkable one is the fpecies which, from is manner of carrying its head and the fore part of its body, erect, he has called the fphinx. A fecond is extreamly remarkable in its hinder part, where it carries two long and immoveable pipes, Handing in a line with the body. Thefe are plainly hollow, and, when the animal pleafes, there iflues out from them a kind of tail, which is very long and flexible, and turns with great eafe any way the creature pleafes. The ufe this is deligned by nature for, feems the wiping off any thing, that may incommode the crea- ture, from any part of its body. Mr! Reaumur never law this tail proceed out of more than one of thefe pipes at a time ; but it feems probable that there is a tail to each pipe, fince their ftrudture feems wholly the fame, and it is eafy to fee of what great ufe this part may be to the creature that poffcflts it.
There is alfo another caterpillar to which the author has given a name, as to the fphinx, from its peculiar attitudes ; this he calls theziczac. Thiscreatureis diftinguilhed fromall the other cater- pillars by the ftrange and unnatural motions (as they appear to us) into which it is continually twilling and bending its body. Befide the common actions of all the caterpillar kind, which are daily feen, and the caufes and ends of which are evidently known, there are others which are very myftcrious. Some caterpillars fpin all the way as they walk, and leave behind them, wherever they pafs, a thread of filk, which marks their journey. A wafte of this kind might appear, at firft fight, very unnatural, and very prejudicial to the creature ; but na- ture has provided for it by a proper fupply ; and if we trace the creature's journey till we chance to fee it fall by accident, we (hall then fee that this thread is not abfolute wafte, for it then preferves the creature, being fattened, to the leaf and twigs it paffes over, and being of ftrength to fupport the hanging weight of the animal, without breaking. It in this manner flops the creatures fall, for it is in its own power to ceafe fpinning when it pleafes ; and if it does not wholly ceafe, fo that the fall is not entirely ftopp'd, it is, however, at leaft, made very eafy. Nor is this all the advantage, for it can, if it pleafes, by means of this thread, re-afcend to the place from whence it fell, by feizing the thread between its legs, and by the help of its head and thefe, gathering up the thread, and replacing itfelf on the leaf ; when it is fafely got up again, it difengages its legs from the thread, and continues its mo- tions as before, and feems no way affecled by the accident. Another very curious and myfterious artifice, is that by which fome fpecies of caterpillars, when the time of their changing into the chryfalis ftate is coming on, make themfelves lodge- ments in the leaves of trees, by rolling them up in fuch a manner, as to make themfelves a fort of hollow cylindric cafe, proportioned to the thicknefs of their body, well de- fended againft the injuries of the air, and carefully fecured for their ftate of tranquillity. The niceft pair of bands could not roll up thefe leaves more elegantly than it is done by thefe little creatures, which have neither hands, nor any thing analogous to them, for the doing it with. Thefe cafes have fometimes five or fix turns, and the manner of the creature's performing the work is this ; when it is to be done, the caterpillar places itfelf on the upper fide of a leaf, at fuch a diftance from the edge, that it can, at plea- fure, reach it with its head, and in turning itfelf round, it can then bring this edge of the leaf to another point, or place, exactly oppofite to it. It then draws lines from this edge of the leaf to this before-mentioned point ; and, doing this all the way along the leaf, its narrownefs toward the point makes it form a clofe cafe there, tho' it did not fo where it began. It flrengthens this firft bending of the leaf by many parallel threads, and when it has perfectly fecured it, it then faflens other threads to the back part of the leaf in this already half form'd circle, and fixing thofe to another point, it draws them as tight as it can, and the bending of the leaf is finilhed, and the cafe of the animal form'd. The fame method repeated makes the feveral after turns, and, by this ingenious con- trivance, the lodging is at length compleatly finilhed. The creature continually adds to the ftrength of its threads, by bringing others acrofs them in different direftions, and fo continues it, that in the five or fix rolls that it makes, every one makes the force of the laft, or more inner one, ufelefs. The cafe being thus compleated with walls fo many times
doubled,
