There is also a very curious and beautiful nest formed by a rare insect, which has only yet been observed in its caterpillar state; but its proceedings therein are interesting and highly remarkable. The length of the body in this caterpillar varies from six to eight inches, the thickness is half a line. The general colour is bluish green, tending to yellow about the head; the feet are black, and six in number. At the extremity of the body are two points projecting sideways. The eyes are visible and prominent in this caterpillar, and besides the antennæ there are two or three pairs of palpi or feelers, which perform the office of hands. This insect inhabits the nut-tree, and cuts out from its leaves a most ingenious case, which serves for its dwelling-place. This case is of a singular form, being an elongated cone, very narrow at the extremity, and tolerably wide at the orifice. It is formed of a strip of nut-leaf, wound up in a spiral manner, but so cleverly contrived that the strip is very narrow at the extremity, and gradually widens as the work proceeds. This happens from the gradual progress of the work, which is begun in the early stage of the caterpillar’s existence, when it does not require a large dwelling-place, and becomes more and more extended to suit the growth of its inmate. When it is completed, it is rather more than an inch long, and two lines in diameter at the orifice. The outside of the case presents the upper surface of the leaf in which the indentations are preserved. The dwelling is a spacious one for the caterpillar, so that it can turn round in it with perfect ease. The band of which the cone is composed is taken from the edge of the leaf, which the caterpillar cuts away in proportion as it winds it round its own body. When one portion has taken the required form, a little more is cut out, but always in a direction parallel with the edge of the leaf. While the insect is thus gradually rolling itself up in a case, it also feeds vigorously on the leaf, taking care, however, always to spare the band which forms its habitation. Another part of the cleverness of this insect consists in maintaining this strip of leaf in its spiral form, which would otherwise naturally unwind by its own weight, and flutter in the wind as a torn fragment. Here it is that silk is again skilfully employed. The caterpillar commences much as other leaf-rolling insects do, by fastening a thread to the edge of the leaf and drawing it towards the desired point. But as the work proceeds the insect generally has three skeins or bands of silk extended from the opening of its case to the leaf. The first is the shortest and the most direct, issuing from the interior of the roll; the second is fastened to the middle of the last spiral, and extends to the leaf; the third is more extensive still, and all three are admirably disposed for keeping the leaf bent to the proper form. These skeins are composed of a great number of threads parallel with each other, which not only serve to retain the leaf in its spiral form, but also serve the caterpillar as a kind of ladder, by which it mounts, and on which it rests while cutting out fresh portions of leaf.
LEAF-NEST UNWOUND.
It sometimes happens accidentally to this caterpillar that the case becomes detached from the leaf, or naturalists have purposely severed a portion to see what would be the result; but this does not greatly disturb the insect, for as long as a single thread of silk remains to hold the pieces together, the caterpillar is able to repair the evil. It will unite the fractured portion almost imperceptibly by means of silken threads, and proceed with its case as before; but if the leaf dry up and wither, the insect is then compelled to desert it, and to select a younger and fresher leaf for its operations.
What is still more curious, on the completion of the dwelling, the caterpillar sometimes wishes to make an excursion to another part of the leaf, and to take its house with it, and this it accomplishes in the following manner. Coming more than three parts out of the cone, the creature makes new skeins in advance of the old, and attempts to pull the cone forward by their means; but finding that this does not succeed, it bends its body back, and quickly severs the old threads and the portion of leaf which keeps the case immovable. It is now able to draw the case onwards a certain distance, after which it has only to repeat the operation, and make other new skeins in advance of these, to continue its onward journey. Thus it arrives at the opposite edge of the leaf, where it carefully adjusts its case to the under side, fastening it with great ingenuity, and drawing the threads tighter where the cone is not properly balanced. In all these cases, silk is the useful material by which the caterpillar secures its nest, and provides for its own safety: it is also a constant resource in case of danger, or of accident, as the following anecdote will show. A caterpillar of the goat-moth, being confined in a smooth glass sugar-basin, managed to crawl up the slippery sides and escape. This excited great surprise in the naturalist (Rösel) who had imprisoned the creature, and he therefore took occasion closely to watch its proceedings when again placed in a similar vessel. It was with surprise and admiration that he now saw the caterpillar constructing a silken ladder on the side of the glass; the natural gum of the silk being sufficient to secure it even to that perfectly smooth surface. Up this ladder the creature crawled, and thus easily and expeditiously made its escape.
SILKEN LADDER SPUN BY THE GOAT-MOTH CATERPILLAR.
Silkworms abound in our own country, as well as in others; but the silk they spin is too fragile and scanty to be employed for other purposes than their own. It is different with some of the caterpillars of India. Although the great supply of silk is there obtained, as with us, from the silkworm of the mulberry-tree, yet the caterpillars of various moths also furnish a considerable quantity. The most important of these are the Tusseh and Arindy silkworms, both natives of Bengal. The first feeds on the leaves of the jujube tree and of the asseen, and is found in such abundance as from time immemorial to have afforded a constant supply of coarse, dark-coloured silk, which is woven into a cheap but very durable cloth.
THE TUSSEH SILKWORM.