Because the coldness of the winter would be fatal to the life of the young insects; and the absence of vegetation would leave the caterpillars to perish of starvation, if they were developed during the winter months.
Fig. 76.—CATERPILLAR FEEDING.
1289. Why do caterpillars appear in the spring?
Because the increasing warmth of the sun developes the living embryo, at the same time that it developes the vegetable germ. The warmth, therefore, that calls the caterpillar from its embryo sleep, also kindles the germinating power of the vegetable upon which it is destined to feed. The worm awakes and finds the bountiful table of nature spread for it.
"Thou shalt plant vineyards, and dress them, but shalt neither drink of the wine, nor gather the grapes: for the worms shall eat them."—Deuteronomy xxviii.