LEPIDOPTERA.
This order of insects is known popularly by the names of Butterfly and Moth. Linnæus gave them the name of Lepidoptera, meaning insects with scaly wings (λεπις, a scale; and πτερον, a wing). They are to be found in great numbers in all parts of the world. All the insects contained in the order are, in their perfect state, remarkable for the elegance of their shape, the rapidity and airiness of their flight, and the multiplicity and beauty of their colours. Before they arrive at this perfect state, the Lepidoptera have to undergo three complete transformations. They leave the egg in the larva or caterpillar state; they pass next to the state of pupa, or chrysalis; they then assume, after a variable time, their final or perfect form. We will study them in their three different states in succession.
When the winter has stripped the leaves off the trees, the Lepidoptera are seen no more; but as soon as the leaves begin to show themselves on the trees and shrubs, this tribe of the insect race again makes its appearance. Caterpillars of all kinds are gnawing at the leaves, even before they are fully developed. Many of them have just emerged from the eggs which the perfect insects had laid at an earlier period; others have passed the winter in this state.
When they come out of the egg the young caterpillars are in shape more or less elongated and cylindrical. Their body is composed of twelve segments, or rings. In front is the head; then come three segments, on which are the front legs, and which constitute the thorax; the other segments constitute the abdomen. The head is formed of two scaly parts. It is often very deeply hollowed out on its upper side, and divided into two lobes, which contain in the angle formed by their separation the different parts of the mouth. The head is uniform, rarely having, so far as our cater pillars are concerned, any protuberance; but in the tropical species it is often armed with prickles, spikes, and extraordinary appendages. They are provided with six small simple eyes, isolated from each other. The mouth is armed laterally with a pair of very solid horny mandibles, articulated by means of vigorous muscles, and moving horizontally. It is the function of the mandibles, as with the jaws, to divide the creature's food. On the middle of a broad under-lip one may perceive a little elongated tubular organ, pierced with a microscopic orifice. This organ is the spinning apparatus, which the animal uses in fabricating the threads which it will one day require. It is a tube composed of longitudinal fibres. It presents only one orifice, cut obliquely, and capable of applying itself exactly to the body on which the larva is placed. From the contractile nature of this organ and the form of its orifice, combined with the faculty the insect possesses of moving it in all directions, result the great differences we observe in the diameter and form of the threads.
Fig. 94.—Scaly legs of the Caterpillar of the Gipsy Moth (Liparis dispar).
The external organs of the trunk and abdomen are the legs, the spiracles, and various occasional appendages. The legs are of two different kinds. The one, to the number of six, attached by pairs to the trunk, are covered with a shiny cartilage, and armed with hooks. These are the true legs. [Fig. 94] represents, after Réaumur's "Mémoire sur les Différentes Parties des Chenilles," [36] the scaly legs of the caterpillar of the Gipsy Moth. The others are membranous, fleshy, generally conical or cylindrical, contractile, and taking, according to the will of the animal, very different forms. [Fig. 95] represents, after the same Memoir of Réaumur's, the different forms of the membranous legs of the silkworm caterpillar. This plate gives a sufficiently good idea of the shape of these organs, and of the hooks, circular or semi-circular, with which they are furnished.