In Meloë the freshly hatched larva, or “triungulin” (Fig. 639, a), is an active Campodea-like larva, which runs about and climbs up flowers, from which it creeps upon the bodies of bees, such as Anthophora and Andrena, who carry it to their cells, wherein their eggs are situated. The triungulin feeds upon and destroys the eggs of its hostess. Meanwhile its inactive life in the bee’s cell reacts upon the organism; after moulting, the-second larval form (Fig. 640, b) is attained, and now the body is thick, cylindrical, soft, and fleshy, and it resembles a lamellicorn larva, with three pairs of rather long thoracic legs. This is Riley’s carabidoid stage. This second larva feeds upon the honey stored up for the young or larval bees. After another moult, there is another entire change in the body; it is motionless, the head is mask-like without movable appendages, and the feet are represented by six tubercles. This is called the semipupa or pseudo-pupal stage. This form moults, and changes to a third larval form (c), when apparently, as the result of its rich, concentrated food, it is overgrown, thick-bodied, without legs, and resembles a larval bee.
Fig. 640.—Oil-beetle: a, first larva; b, second larva; c, third larva; d, pupa.
Fig. 641.—History of Sitaris: a, triungulin or 1st larva; g, anal spinnerets and claspers of same; b, 2d larva; e, pseudo-pupa; f, 3d larva; c, true pupa; d, imago, ♀.—After V. Mayet, from Riley.
After thus passing through three larval stages, each remarkably different in structure and in the manner of taking food, it transforms into a pupa of the ordinary coleopterous shape (d).
The history of Sitaris, as worked out by Fabre and more recently by Valery-Mayet, is a similar story of two strikingly different adaptational larval forms succeeding the triungulin or primitive larval stage. The first larva (Fig. 641, a) is in general like that of Meloë, the second (b) is thick, oval, fleshy, soft-bodied, and with minute legs, evidently of no use, the larva feeding on the honey stored by its host. The pseudo-pupal stage is still more maggot-like than in the corresponding stage of Meloë, and the third larva (f) is thick-bodied, with short thoracic legs.
In the complicated life-history of another cantharid, Epicauta vittata, as worked out by Riley (Fig. 642), we have the same acquisition of new habits and forms after the first larval stage, which evidently were at the outset the result of an adaptation to a change of food and surroundings. The female Epicauta lays its eggs in the same warm, sunny situation as that chosen by locusts (Caloptenus) for depositing their eggs. On hatching, the active minute carnivorous triungulin, ever on the search for eggs, on happening upon a locust egg gnaws into it, and then sucks the contents. A second egg is attacked and its contents exhausted, when, owing to its comparatively inactive habits and rich nourishing food after a period of inactivity and rest, the skin splits along its back, and at about the eighth day from beginning to take food the second larva appears, with much smaller and shorter legs, a much smaller head, and with reduced mouth-parts. This is the carabidoid stage of Riley. After feeding for about a week in the egg a second moult occurs, and the change of form is slight, though the mouth-parts and legs are still more rudimentary, and the body assumes “the clumsy aspect of the typical lamellicorn larva.” This Riley denominates the scarabæidoid stage of the second larva.
Fig. 642.—Epicauta cinerea: a, end of 2d larval stage; b, portion of dorsal skin; c, d, coarctate larva; e, f, pupa.—After Riley.