Though the reasons for it are still unknown, modern research has shown us how this incredible change has taken place.
When this creature, which has grown a hundred times its size since it was born, has reached the age for this great change, it doubtless feels the impending transformation coming, and instinct tells it to crawl away into some protected nook or corner and pupate underneath the protection of a silken coverlid of its own spinning.
The change begins; each organ goes to pieces, disintegrates, becomes a mass of disconnected cells, so that the body filled with these, becomes, as it were, a bag of mush. This mushy fluid has been likened by entomologists to the disintegrated tissues which inflammation causes in our own bodies. If, then, you should slit it open at this stage, you would find no alimentary canal, no salivary glands, no muscles, simply a thick fluid, with here and there a thicker lump, that is attached at certain places to the inside of the sac wall. These lumps are formed of groups of active cells which were not disintegrated in the general breakdown of the muscle tissue, and these form the nuclei around which the new creature is to be built. These groups of cells grow rapidly, feeding on the fluid mass of broken-down tissue much as a young chick inside the egg feeds on the yolk, and builds up the whole complicated structure of the winged beetle, which seems to have no possible relations to the white grub out of whose body it was made.
It is as though the insect hatched twice, first from the almost microscopic egg its mother laid and from which it emerged as a tiny little creature in the image of this grub, growing and manufacturing from the leaves it eats enough nitrogenous matter so that when it emerges again from the yolk-like substance of its cocoon it will be a full-grown beetle, for it must be remembered that once made the beetle never grows.
This wonderful process is the same which is gone through by every flying insect that has a grub or caterpillar stage.
ONE OF THE JUNE BUGS OR MAY BEETLES
(Lachnosterna quercus, Knoch)