Ferocious-looking Praying Mantids eat a wide variety of insects, and since they dont fly, they stay right in the area where they are released. In their younger stages, praying mantids eat aphids, thrips, flies and maggots, small caterpillars, leafhoppers, white grubs and other soft-bodied insects. Mature mantids feed on larger caterpillars, earwigs, chinch bugs, sow bugs, beetles, grasshoppers and other large insects. Praying mantids are completely harmless to people, pets, and the environment. Each egg case, about the size of a ping pong ball, contains about 200 eggs, which hatch when the weather becomes warm.