After several moultings or castings of the skin, to allow of the growth of the insect (for insects grow only in the larval state), the larva becomes transformed into the pupa ([Pl. X.] fig. 8). In this state the animals still move about in the water, and are often found suspended from its surface by two respiratory tubes, which, however, are not connected with the tail, but arise from the thorax; and the various parts of the perfect insect may be seen through the case or skin, within which they are closely packed.
When the pupa has attained its full development, the perfect insect emerges from it, leaving the water to fly about and seek food.
Tipu´lidæ.—In the water of ponds and pools a young larva ([Pl. X.] fig. 31) will often be met with, which is that of Chiron´omus plumósus, a largish gnat-like insect, belonging to the daddy-long-legs family (Tipulidæ). This larva exhibits the usual thirteen segments, including the head. In the young state the body is nearly colourless; but in the mature larva it is of a blood-colour, and about an inch in length. Beneath the first joint of the body are two foot-like processes covered with hair; and at the end of the body are also two processes, surmounted with hooks. The three last joints of the body are also furnished each with a pair of fleshy processes, those of the first pair being very short.
Hymenop´tera (ὑμἠν, membrane, πτερὀν, wing).—This, which forms the sixth Order of insects, contains the bee, the wasp, the ant, &c.
In the Hymenoptera there is a curious contrivance for linking the two wings on each side, so that they may form a single piece in the flight of the insect. It consists of a row of hooks, placed upon the anterior nerve of the hind wing, which play upon the folded-in corresponding edge of the fore wing; the hooks, sliding along this edge, allow of freedom of motion, although still holding the two wings together. This structure may be well seen in the wings of the Humble Bee when mounted in balsam.
The sting of the wasp and bee is also a singular organ. In both insects it is much alike, consisting of a sheath, slit up beneath, in which are contained two long setæ, or lancets, with bent-back (recurved) teeth near the end. These setæ are inserted into the flesh during the act of stinging, and at the same time the poisonous secretion from two glands is forced into the wound, which causes the severe pain resulting from the sting.
In the wingless neuters of the common ant, attached to the end of the tibia ([Pl. X.] fig. 34 c) is a beautiful pectinate process, somewhat resembling a comb (fig. 34 a).
Lepidop´tera (λεπἰς, scale, πτερὀν, wing).—This Order contains the butterflies and the moths, the entire bodies of which are covered with minute scales. When the insects are handled, these scales adhere to the fingers as a fine dust; and on pressing a slide against the insects, they may be removed for examination. They consist of a very slender and short quill, by which they are attached, and a flattened plate of various forms ([Pl. X.] fig. 19, b, f); it is, however, generally narrower near the quill, and expanded towards the free end, where it is often cut into lobes or toothlike segments. The scales are usually covered with continuous longitudinal lines or ridges, with granules of colouring-matter (pigment) situated between the two thin layers of which the scales consist. In some of them the form is that of a filament, either simple or branched at the end (fig. 19 e), when they resemble minute hairs. In the males of the large white Cabbage Butterfly (Pi´eris brass´icæ), certain of the scales of the wings are covered with longitudinal rows of very minute dots (fig. 19 f), and have little tassel-like bodies at the end. The males may be distinguished from the females by the front wings having no black spots, while those of the females have two upon each wing. When the scales are examined as they exist upon the wings of the Lepidoptera, they are found to be imbricated ([Pl. X.] fig. 3) or overlapping each other like the tiles on the roof of a house.
The Lepidoptera suck the honey of flowers by means of a spiral tongue ([Pl. X.] fig. 20 c) or ant´lia (antlia, a sucking-tube); this consists of two halves, which represent the maxillæ of other insects; and their margins are fringed with little tassel-like bodies, probably organs of taste. The antennæ (fig. 20 a) are many-jointed, clubbed at the ends (d) in the butterflies, and simple in the moths. The palpi (fig. 20 b) are short and densely covered with scales. In the large eyes the facets are very distinct and suitable for examination.
The larvæ are well known as caterpillars. They have six legs, as in the perfect insects, but rudimentary and with single claws; also some additional pairs of pro-legs, as they are called, with a crown of hooks, towards the hind part of the body. The spiracles of caterpillars are very favourable for observation.