The plant galls mostly develop directly after the female insect lays the eggs. The inducement for the gall formation is largely unknown; discussion speculates as to chemical, mechanical, and viral triggers. The hatching larvae nourish themselves with the nutritive tissue of the galls, in which they are otherwise well-protected from external environmental effects. The host plants, and the size and shape of the galls are specific to the majority of gall wasps, with about 70% of the known species parasitizing various types of oak trees. Galls can be found on nearly all parts of such trees, including the leaves, buds, branches, and roots. Other species of gall wasps live in eucalyptus trees, rose bushes or maple trees, as well as many herbs. Frequently, the determination of the species is much easier through observation of the galls produced rather than the insect itself.