A great variety of deformations and growths produced by insects and mites as well as by fungi have been described.
While the majority of the Thysanoptera are thus vegetarian in their diet, and are frequently injurious in farm and garden, some species, at least occasionally, adopt a predaceous habit, killing aphids and small mites (so-called "red-spiders") and sucking their juices.
On patting their carrier or some passing ant, the mites are supplied with food, no service being rendered by them in return for the ants' care.
Zukal has considered that the lichen acids protect the lichen from the attacks of animals; the experiments of Zopf, however, have cast doubt on this; certainly lichens containing very bitter acids are eaten by mites though some of the acids appear to be poisonous to frogs.
Among the simplest examples of the former are the hairs which follow the irritation of the cells by mites.