This hastening of the natural events of insect life is known as forcing, and merely consists in subjecting the species concerned to a reasonable amount of artificial heat, such as that of a room in which a fire is always kept, or of a hothouse.
It is interesting at all times to note the dates on which eggs are laid or collected, and the times at which the young larvæ appear. In addition to this all changes that take place in the colours or forms of eggs should be carefully observed; for such changes will assist you in distinguishing between fertile and sterile ova, and also enable you to judge approximately as to the date of the appearance of future broods.
Rearing Larvæ
The main point in connection with the rearing of larvæ is certainly the selection and construction of the cages or their substitutes. For newly hatched and all very small caterpillars a small bottle with a wide mouth makes a very fair abode. Put a layer of sand or sifted soil in the bottom, fix in this a small twig of the food plant or lay a few leaves on the top, and then, after the larvæ have been introduced, cover the top with a piece of muslin, held in place by an elastic band.
The great drawback with this arrangement is the lack of any provision for keeping the food moist and fresh, thus rendering a change necessary at very frequent intervals; but this may be obviated by using damp sand as a foundation for the little twig of food plant. With this improvement, if you cover the top of the bottle with apiece of glass, a saucer, or any impermeable substance, you may keep the twig fresh for several days, generally until the disappearance of the last leaf calls for a fresh supply; but it is
very doubtful whether the damp atmosphere resulting from this inclosure is not injurious to the larvæ. It certainly does not seem to have much influence on some, but the unhealthy conditions that result must be detrimental to the inmates. It must also be remembered that many species require a dry soil in which to burrow when about to change.
When the time comes for the change of food, great care must be taken not to injure young and small larvæ. In many cases they need never be touched, for if a fresh twig be placed beside the stale one, they will readily find their way to it; and to facilitate this, and also to afford a convenient foothold to those larvæ that accidentally fall from the twig, the layer of sand at the bottom of the bottle should be covered with moss or cocoa-nut fibre.
Fig. 57.—A Larva Glass.