Bug FAQOak Marble Gall Wasp
Andricus kollari · Order: Hymenoptera · Family: Cynipidae
Also called: Marble Gall
Source: Wikipedia
Adult oak marble gall wasps are tiny dark-brown insects about 1.5 to 2 mm long. They induce round green-then-brown galls up to 25 mm on oak buds, which mature in late summer. The wasp needs Turkey oak to complete its two-year life cycle, alternating sexual and asexual generations.
Source: Wikipedia
How to recognize it
Adults are dark brown and very small, about 1.5 to 2 mm long.
Source: Wikipedia
Size
The wasp measures roughly 0.06 to 0.08 inches in length.
Source: Wikipedia
Is it a pest in the house?
They may appear in large numbers but cause no measurable harm. Removing galls before they dry can reduce their numbers.
Source: Wikipedia
How to get rid of it
Destroying galls before the wasps emerge helps keep the population low.
Source: Wikipedia
Where it lives
It creates parasitic galls on oak trees where it lays its larvae.
Source: Wikipedia
What it eats
The galls contain tannic acid, historically used for ink and dye. Various harmless insects live inside the gall, and some are parasitised.
Source: Wikipedia
Life cycle
It alternates sexual and asexual generations, each taking about two years. A single female larva develops inside each spherical gall and emerges as an adult in September.
Source: Wikipedia
When you see it
In May-June, sexual females lay eggs in developing oak buds. Spring adults are the sexual generation that start the summer marble gall.
Source: Wikipedia
Where it comes from
Turkey oak, introduced to Britain in 1735, is required for its life cycle.
Source: Wikipedia
Lookalikes
They are often confused with oak apple galls made by Biorhiza pallida. Stunted forms can be mistaken for the Cola-nut gall of A. lignicola.
Source: Wikipedia
More photos
Questions people ask
Do oak marble gall wasps damage my garden or trees?
They cause no measurable harm to trees or gardens.
Source: Wikipedia
How can I reduce oak marble gall wasps?
Remove and destroy the galls before they dry and the adults emerge.
Source: Wikipedia
What do the galls look like?
They start as green rounded masses on oak buds and later become hard, brown, and up to about 25 mm across.
Source: Wikipedia
When do the wasps appear?
Sexual adults emerge in spring, and the asexual adults emerge in September from mature galls.
Source: Wikipedia
Same family (Cynipidae)
Sources
- Wikipedia: https://en.wikipedia.org/wiki/Andricus_kollari
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Text written 2026-10-23 from the sources above and checked sentence by sentence against them. Data fetched 2026-10-22.