Andricus kollari, Oak Marble Gall

Common Name: Oak Marble Gall

These galls, on our traditional English oak, Quercus robur, are caused by a minute gall wasp, Andricus kollari. Formed in buds, they can grow up to about 25mm in diameter. The gall starts life green in colour, but changes to brown by the autumn, when the adult wasps emerge.

With a length of 1.5 to 2mm, the male wasp is very dark brown to black on the head, has a hunched thorax and a black abdomen. The legs are yellowy brown and the antennae are a translucent yellow/brown colour. The female has a dark brown appearance overall.

The gall is seen more often than the adult wasp. The empty gall, now showing a neat little hole in the side where the wasp emerged, remains on the twig. Like most gall wasps, the life cycle is complicated, with an alternation of a sexual and asexual generation each year.

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