After six or seven days there is another transformation, the skin being cast, and the insect passes into another stage, “the ultimate stage of the second larva.” The larva, immersed in its rich nutritious food, grows rapidly, and after about a week leaves the now addled and decaying locust eggs, and burrows into the clear sand, where it lies on its side in a smooth cell or cavity, and where it undergoes an incomplete ecdysis, the skin not being completely shed, and assumes the semipupa stage, or coarctate larval stage of Riley.
In the spring the partly loose skin is rent on the top of the head and thorax, and then crawls out of it the “third larva,” which only differs from the ultimate stage of the second larva “in the somewhat reduced size and greater whiteness.” The insect in this stage is said to be rather active, and burrows about in the ground, but food is not essential, and in a few days it transforms into the true pupa state.
These habits and the corresponding hypermetamorphosis are probably common to all the Meloidæ, though the life-history of the other species has yet to be traced.
In the genus Hornia described by Riley, the wings of the imago are more reduced than in any other of the family, both sexes having the elytra as rudimentary as in the European female glow-worm (Lampyris noctiluca). These, with the simple tarsal claws and the enlarged heavy abdomen, as Riley remarks, “show it to be a degradational form.”
Its host is Anthophora, and the beetle itself lives permanently in the sealed cells of the bee, and Riley thinks it is subterranean, seldom if ever leaving the bee gallery. The triungulin is unknown, but the ultimate stage of the second larva, as well as the coarctate larva, is like those of the family in general, the final transformations taking place within the two unrent skins, in this respect the insect (Fig. 643) approaching Sitaris.
It appears, then, that as the result of its semi-parasitic mode of life the Campodea-form or triungulin larva of these insects, which has free-biting mouth-parts like the larvæ of Carabidæ and other carnivorous beetles, instead of continuing to lead an active life and feeding on other insects; living or dead, and then like other beetles directly transforming into the normal pupa, moults as many as five times, there being six distinct stages before the true pupa stage is entered upon. So that there are in all eight stages including the imaginal or last stage.
One cannot avoid drawing the very obvious conclusion that the five extra stages constituting this hypermetamorphosis, as it is so well styled, are structural episodes, so to speak, due to the peculiar parasitic mode of life, and were evidently in adaptation to the remarkable changes of environment, so unlike those to which the members of other families of Coleoptera, the Stylopidæ excepted, have been subjected. The fat overgrown body and the atrophied limbs and mouth-parts are with little doubt due to the abundant supply of rich food, the protoplasm of the egg of its host, in which the insect during the feeding time of its life is immersed. Since it is well known that parthenogenesis is due to over, or at least to abundant nutrition, or to a generous diet and favoring temperature, there is little reason to doubt that the greatly altered and abnormally fat or bloated body of the insect in these supernumerary stages is the result of a continuous supply of rich pabulum, which the insect can imbibe with little or no effort.
Fig. 643.—1, Egg-pod of Caloptenus differentialis with the mouth torn open, exposing the newly hatched larva of Epicauta vittata (1 a) eating into an egg and the passage which it made through the mucous covering; natural size. 2, dorsal view of the 1st larva, or triungulin, of E. vittata; 2 a, one side of the head of same from beneath, greatly enlarged so as to show the mouth-parts; 2 b, terminal joint of maxillary palpus, showing imbrications and flattened inner surface armed with stout points; 2 c, leg, showing more plainly the tarsal spines; 2 e, labrum; 2 d, one of the abdominal joints from above, showing stout points, stigmata, and arrangement of spinous hairs. 3, eggs of E. vittata, the natural size indicated at side. 4, dorsal view of the carabidoid stage of the 2d larva of E. vittata: 4 a, its antenna; 4 b, its right maxilla; 4 c, its leg; 4 d, side view of same, showing its natural position within the locust-egg mass. 5, lateral view of the ultimate or full-grown stage of the 2d larva of E. vittata; 5 a, portion of the dorsal skin, showing short setaceous hairs. 6, third head, or that from the scarabæidoid stage of the 2d larva of E. vittata from beneath, showing the reduction of mouth-parts as compared with the first head (2 a); 6 a, antenna of same; 6 b, maxilla of same; 6 c, mandible of same. 7, fourth head, or that of the full-grown larva of E. vittata, from above; 7 a, leg of same; 7 b, the breastplate or prosternal corneous piece. 8, lateral view of the pseudo-pupa or coarctate larva of E. vittata, with the partially shed skin adhering behind: 8 a, dorsal view of same; 8 b, its head, from the front; 8 c, same from side; 8 d, tuberculous leg; 8 e, raised spiracle; 8 f, anal part of same, 9. lateral view of the true pupa of Epicauta cinerea Forst: 9 a, ventral view of same. 10, Epicauta vittata (lemniscata or trivittate var.). 11, Epicauta cinerea Forst. (= marginata Fabr.). 12, antenna of the triungulin of Epicauta pennsylvanica: 12 a, maxilla of same; 12 b, labial palpus of same. 13. ♂ Hornia minutipennis, dorsal view; 13 a, lateral view of same; 13 b, simple claw of same; 13 c, coarctate larva; 13 d, leg of ultimate stage of 2d larva.—After Riley.
