Cauliflower Gall Mite - Aceria fraxinivora

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 inflorescence 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; sometimes called Cauliflower Galls. 

Gall Adult

Anywhere that Ash is present.

Galls are often visible all year round.

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

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

Common in Leicestershire and Rutland.