Biorhiza pallida, Oak Apple Gall

Common Name: Oak Apple Gall

This is one of our most well-known galls. It occurs on both our native oak species, as well as other oak species, and can be found across the UK. It’s caused by the oak apple gall wasp Biorhiza pallida.

The wasp lays her eggs inside a dormant leaf bud, which then hatch in spring and start the process for the formation of galls. These galls tend to drop from the trees in June, when the larvae are mature and ready to fly. However, some remain on the tree, going very woody. Inside the gall, there are a number of chambers, each housing a larva which eats its way out. Adults emerge in June and July.

The wasp has a second generation: the females that emerge in spring mate and drop to the ground to lay eggs in oak roots, producing further galls. The wingless adults that emerge then climb their way back up the tree, lay eggs, and the whole process starts again.

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