Why does the hemorobius perla fasten its eggs to the leaves of trees, upon upright bristle-like points?

Because the aphis has previously laid its eggs upon these leaves, and the young aphides would destroy the above eggs, were they not thus kept out of their reach. As soon as the larvae of the hemorobius appear, they crawl down the slender props upon which they rested, and commence devouring the aphides, wherefore the former are termed plant louse lions; and by thus thinning them, they are doubtless of great service in the general economy of nature.