Independent of the method of collecting caterpillars by an attentive examination of the leaves, and other parts of plants, at those times of the year when they are in full verdure, there is another, viz. by beating the boughs of trees, particularly the taller ones, with long poles, having previously spread a large sheet underneath to receive them as they drop from the trees. By these means many very valuable caterpillars are frequently obtained, which could not otherwise be procured without considerable difficulty. Caterpillars should be handled as little as possible, particularly those with smooth skins; the more hairy ones in general sustain less injury by it. To convey them home with safety, the collector should be provided with a chip box in his pocket; and it would be proper to have it partly filled with fresh leaves.
THE METHOD OF REARING OR BREEDING THEM.
Having procured the caterpillars, our next endeavour must be to rear them. For this purpose; it will be indispensably necessary to afford them an ample supply of the plant on which they are found feeding, and to renew their food as often as the decay of that first procured for them may render it expedient. Insects in this state usually feed voraciously; the caterpillar of the papilio brassica has been known to consume in one day twice its own weight of food. Although many of them live on a variety of food, the greatest part are attached to some particular kind; deprived of which, some species would form objects less beautiful when arrived at their perfect state, and others infallibly perish.
As to many it may prove very inconvenient to supply the caterpillars with fresh food daily, to avoid this trouble, several sprigs of the tree or plant may be put into a wide-mouthed glass filled with water, and the caterpillars placed on them. Most plants may in this manner be preserved fresh for three or four days. The glass, together with the caterpillars and their food, is to be placed in the breeding box represented in the [figure] annexed, a, shews an opening in the front covered with gauze; b, the door on the side; c, a ring for conveniency of carriage; and a constant supply of fresh food is to be given them, as soon as the former appears in the least withered. The breeding boxes should never be exposed to the scorching rays of the sun, but placed in a cool and shady situation; nor should they contain more than one kind of caterpillar, as some species devour others.
When arrived at their full growth, the caterpillars leave off eating, and soon after, change into the chrysalis or pupa form; previous to which, butterflies spin a little web, just sufficient to suspend themselves by: many of the moths, like the silk-worm, spin a large web, in which they inwrap themselves; and a great number penetrate into the earth, where they spin themselves cases, or change without any spinning, as do most of the sphinges or hawk-moths. It will therefore be necessary to cover the bottom of the box with fine mould to the depth of four or five inches, and keep it constantly moist.
It frequently happens that caterpillars are what the aurelians call stung, that is, have the eggs of the ichneumon-fly deposited in them, of which operation a full account has been given in [pages 295]-[298]. Caterpillars, previous to their going into the chrysalis state, generally lose the brilliancy of their colours, and many of them rove about for some time.
After remaining in their chrysalis state till near the time of their coming forth, such as are inclosed in a hard case or spinning, as the phalæna vinula, puss moth; phalæna quercus, great egger moth, &c. are to be carefully freed from it; as the aperture which the insect naturally makes is often too narrow for it to pass through without sustaining considerable injury in its plumage. The opening will be best made, by cutting off the larger extremity of the case, taking especial care not to wound the inclosed pupa or chrysalis.
The learned Dr. Bellardi, Foreign Member of the Linnean Society, &c. a few years since discovered a new method of feeding silk-worms, when they are hatched before the mulberry-trees have produced leaves, or when the tender branches are destroyed by frost: how far this practice may be successfully applied in other instances, seems as yet undetermined; though from some recent experiments, it appears possible that caterpillars may be thus fed in backward seasons. This method consists in giving the caterpillar-the dried leaves of their accustomed food reduced to powder, and gently moistened with water; a thin coating of which must be placed round the young worms, who will immediately begin to feed upon it. The Doctor informs us that the caterpillars of the silk-worm prefer it to any other food, and devour it with the utmost avidity. The leaves should be gathered towards the close of the autumn, before the frost commences, in dry weather, and when the heat is greatest; they must be dried in the sun by spreading them upon large cloths, and after being reduced into powder, laid up in a dry place. Donovan says,[160] that the experiment has been tried with several caterpillars which were nearly full fed on the leaves of thorns and oaks thus prepared, and that they were observed to eat it when no other food was given, but he cannot determine how far they may thrive if fed on that aliment only.
[160] Treatise on the Management of Insects.