Generally, the Woolly Bear is found feeding on the common blind nettle, but it may often be detected at some distance from its food, getting over the ground at a great rate, and reminding the spectator of the porcupine. In this case it is usually seeking for a retired spot, whither it resorts for the purpose of passing the helpless period of pupa-hood.
If it is captured on such an occasion, there will be little trouble in feeding, as it will generally refuse food altogether, and, betaking itself to a quiet corner, prepare for its next stage of existence.
If taken at an earlier period of its life, it feeds greedily on the nettle above-mentioned, and the amount of nutriment which one caterpillar will consume is perfectly astounding. I once had nearly four hundred of them all alive at the same time, and they used to be furnished with nettles by the armful. Of course so large a number is not necessary for ordinary purposes; but this regiment was required for the purpose of watching the development and anatomy of the creature through its entire life.
As the skins of caterpillars are not capable of growth, and the creature itself grows with singular rapidity, it is evident that the skins themselves must be changed, as is the case with many other animals of a higher class, such as the snakes, newts, &c.
For this purpose the skin of the caterpillar splits along the back of the neck, and by degrees the creature emerges, soft, moist, and helpless. A very short time suffices for the hardening of the new envelope; and as the caterpillar has been obliged to fast for a day or two, previously to changing the skin, it sets to work to make up for lost time, and does make up effectually.
In the case of the Woolly Bear, and several others, the cast skin retains nearly the same shape and appearance as when it formed the living envelope of the caterpillar; and, consequently, if any number of these insects are kept, the interior of their habitation soon becomes peopled with these imitation caterpillars. Each individual changes its skin some ten or eleven times, each time leaving behind it a model of its former self, so that caterpillars seem to multiply almost miraculously.
Although even the exterior appearance of an insect is very wonderful, yet its interior anatomy is, if possible, even more wonderful, and, if possible, should be examined. The mode of doing so is simple and easy. If the Woolly Bear, for example, is to be dissected, the easiest mode of doing so is as follows:—
Get a shallow vessel, glass if possible, about an inch or so in depth; load a flat piece of cork with lead, put it at the bottom of the vessel, and fill it nearly to the top with water. Now take the caterpillar, which may be killed by a momentary immersion in boiling water, or by being placed in spirits of wine, and with a few minikin pins fasten it on its back on the cork. The pins of course must only just run through the skin, and two will be sufficient at first, one at each end.
Now take a pair of fine scissors, and carefully slit up the skin the entire length of the creature, draw the skin aside right and left, and pin it down to the cork.
The creature will now exhibit portions of organs of different shapes and characters, the remainder being concealed under the mass of fat that is collected in the interior. This fat must be carefully removed in order to show the vital organs; and this object is best attained by using a fine needle stuck into a handle. I generally use a common crochet-needle handle, so that needles of various sizes can be used at pleasure.