Oak Apple Gall Wasp

Oak Apple Gall Wasp

Sunday 28th April 2019

Scientific name: Biorhiza pallida
Living up to its name, the Oak Apple Gall Wasp produces growths, or 'galls', on oak twigs that look like little apples. Inside the gall, the larvae of the wasp feed on the host tissues, but generally does not cause damage to the oak tree itself.

The Oak Apple Gall Wasp, Biorhiza pallida, is a tiny wasp that causes 'galls' on oak twigs and leaves. These galls can usually be found between May and June where the female has laid her eggs in the leaf bud. When the larvae hatch, chemical and hormone interaction between the wasp eggs and the oak causes the tree to grow the round gall. Inside the gall, there are a number of chambers, each housing a larva which eats its way out.

How to identify
The Oak Apple Gall Wasp produces a large, rough, buffish-brown, apple-like gall that can be found on oak twigs. If the galls you see are green with brown spots, they are still forming. At this stage, the galls feel a little rubbery. The galls get bigger as the larvae get bigger. When the galls dry out, the oak apple gall wasps fly from small holes in the galls.

Did you know?
The Oak Apple Gall 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 which are marble-like. They then hatch and return to the twigs to lay eggs in the buds, and the cycle continues.

How people can help
Our gardens are a vital resource for wildlife, providing corridors of green space between open countryside, allowing species to move about. In fact, the UK's gardens provide more space for nature than all the National Nature Reserves put together. So why not try leaving wilder areas in your garden, such as patches of buttercups in your lawn or nettles near your compost heap, to see who comes to visit?