Cauliflower Gall Mite - Aceria fraxinivora

Alternative names
Aceria fraxinivorus and Eriophyes fraxinivorus

Gall mites are extremely tiny plant feeders, often around 0.5mm in size. They are members of the Arachnid group, which includes spiders and mites, and are small enough to pierce and feed on individual plant cells, causing the surrounding cells to enlarge and multiply to form the gall. The galls that form on the fruiting keys of the Ash tree are caused by the mite Aceria fraxinivora. These galls are irregular, woody encrustations, green at first and gradually turning to brown and black, which remain on the tree for up to two years. In Holland and France they are known as Cauliflower Galls. The mites are sap-sucking elongated cylinders, which apparently have no eyes, circulation or respiratory system and just two pairs of legs. The galls are far easier to see than the mites.

Identification difficulty

Adult Gall


Anywhere that Ash is present.

When to see it

Galls are often visible all year round.

Life History

They are mainly all female, producing eggs which need no fertilization.

UK Status

Very common and widespread in Britain, although numbers seem to vary significantly depending on the number of Ash keys produced in any given year.

VC55 Status

Common in Leicestershire and Rutland.

be our species champion

Leicestershire & Rutland Map


Yellow squares = NBN records (all known data)
Coloured circles = NatureSpot records: 2020+ | 2015-2019 | pre-2015

UK Map