Not the food-instinct alone, but the instinct of self-preservation, of mode of motion, in short, every kind of instinct, may vary in the course of an individual life. Let us follow the somewhat complex life-history of a beetle of the family of the Blister-beetles or Cantharides, as we learnt it first from Fabre. The female of the red-shouldered bee-beetle (_Sitaris humeralis_) lays its eggs on the ground in the neighbourhood of the underground nest of a honey-gathering burrowing-bee (_Anthophora_). The larvæ, when they emerge, are agile, six-legged, and furnished with a horny head and biting mouth-parts, as well as with a tail-fork for springing (Fig. 32, _a_). The little animals have at first no food-instinct, or at least none manifests itself, but they run about, and as soon as they see a bee of the genus _Anthophora_ they spring upon it and hide themselves in its thick, hairy coat. If they have been fortunate the bee is a female, who founds a new colony and builds cells, in each of which she deposits some honey and lays an egg upon it. As soon as this has been done the _Sitaris_ larva leaves its hiding-place, bites the egg of the bee open, and gradually eats up the contents. Then it moults, and takes the form of a grub with minute feet and imperfect masticating organs; the tail-fork, too, is lost, for all these parts are now useless, since it can obtain liquid nourishment without further change of place, from the honey in the cell, in exactly the quantity necessary to its growth. Then it spends the winter in a hardened, pupa-like skin, and it is not till the next year (the third), after another short larval stage (_d_) and subsequent true pupahood (_e_), that the fully-formed beetle emerges. This again possesses biting mouth-parts, and eats leaves, and has legs to run with and wings to fly with. In this beetle, then, the food-instinct changes three times in the course of its life; first the egg of the bee is the liberating stimulus, then the honey, and finally leaves. The instinct of moving about varies likewise, expressing itself first in running and jumping and in catching on, then in lying still within the cell, and, lastly, in flying and running about on bushes and trees.