The petiole connects with the gaster, which is the functional abdomen in apocritan wasps, starting with the third abdominal segment proper.

Together, the petiole and the gaster form the metasoma, while the thorax and the propodeum make up the mesosoma.

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.

Galls can be found on nearly all parts of such trees, including the leaves, buds, branches, and roots.

Some of these inquilines and parasitoids use their long, hardened egg-laying tube (ovipositor) to bore into the gall.

Also striking are the galls of Cynips longiventris, which likewise can be found on the undersides of leaves, and are recognizable for their spheroidal shape and irregular red streaks.

[6] Sawflies (paraphyletic) Ceraphronoidea Ichneumonoidea Cynipidae other families Chalcidoidea and other groups Evanioidea Stephanoidea Trigonaloidea Aculeata (stinging wasps, bees, ants) The internal phylogeny of gall wasps in the cladogram is based on the molecular phylogenetic analysis of Hearn et al.