Clustered Midrib Gall Wasp, Andricus dimorphus
Also called Adleria dimorpha
Cynipidae or Gall Wasp Family

Galls on oak leaf

A very small wasp, only a few millimeters long, with a general wasp-like look and wings that look large for the insect. Females lay their eggs within the midrib of leaves of oaks in the white oak group. The egg hatches to produce a tiny but typical wasp grub. The oak responds to unknown cues by walling off the larva within a round gall. Since the female lays a number of eggs in a cluster, a cluster of galls appears. This is fine with the larva which is mostly protected by the gall and which spends its grubhood munching on the inner tissues of the gall, which are quite nutritious to gall wasp grubs. Eventually the grub becomes an adult which emerges from the gall, usually in the spring, and flies off to mate.

Occasional in Wildwood. Reported to form galls in white oak (Quercus alba) and chestnut oak (Q. prinus), both of which occur in Wildwood.

Easily identified if the leaf can be identified since the cluster of round balls on white oaks is characteristic of this species. The adult is unlikely to be identifiable, or even noticed, by anyone but a wasp expert.

If you want to see an adult, your best bet is to take some galls home, put them in a jar and wait to see what comes out. But, maybe not. Although the gall is a good protection from predators, other tiny wasps parasitize the gall wasps, inserting their ovipositors (egg-laying organs) into the gall and laying an egg in the grub. The parasitic wasp egg then hatches into a grub which eats the gall wasp and emerges in its stead. On top of that, still other wasps parasitize the parasites, laying their eggs in the parasitic grub. So what comes out could be a gall wasp, a wasp that ate the gall wasp, or a wasp that ate the wasp that ate the gall wasp!




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