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Silk Button Gall Wasp

Neuroterus numismalis

Silk Button Gall Wasp

A close up image of Neuroterus numismalis silk button gall wasp galls on a green oak leaf

Neuroterus numismalis 1 beentree

by Beentree. CC BY-SA 3.0

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Oak Gall Wasps are tiny insects that are parasitic to Oak trees. This means they require Oak to reproduce successfully. When Wasps lay eggs in Oak, growths, or galls, appear on plants. Although unsightly, Oak trees can tolerate Gall Wasps. Neuroterus numismalis is a Gall Wasp which causes Oak trees to form pretty, silky, button-shaped galls. If you look at them more closely, it seems as if each gall is made with golden brown thread. Some leaves may possess hundreds of Silk Button Spangle Galls, which begin to appear in summer. Galls fall to the ground in autumn, with mature wasps emerging the following spring. There is a second type of gall which occurs in the spring. This one is more discrete and blister-like, matching the colour of leaves.
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Traits

They cause plants to produce abnormal growths, called galls.
Plant galls won't permanently damage plants.

Appearance

Adults: These wasps are so tiny it's unlikely you'd see them. Galls: In spring, the first generation of wasps lays eggs in the new Oakleaf buds. Blister-like galls are produced on the leaves and can be difficult to spot because they're barely domed and match the colour of leaves. Each has a brown pimple in the centre, surrounded by pale green lines. In late summer, it's possible to see the silk button galls on the underside of oak leaves. These are golden-brown with a glossy shine, measuring roughly 5 mm. They almost look like they're made of embroidery thread. The galls fall to the ground in autumn.

Symptoms

Silky, golden-brown button-like galls under oak leaves. Silk button galls fall to the ground in autumn. Green blister-like galls form in the spring.

Activity

Diurnal

Personality

Order

Hymenoptera

Family

Cynipidae

Metamorphosis

Complete

Distribution

Europe

Biological treatment

This wasp will not impact the longterm yield of trees, but galls may be unsightly. Damage is only aesthetic. Gall wasps seem to be more frequent in some years than others, allowing trees to recover.

Chemical treatment

Insecticides are unlikely to work on this wasp.

Attracts

Oak

Quercus spp.

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