Acalitus brevitarsus is a mite that causes blister like galls to form on the leaves of Alder. Like many mite galls, the leaf is made to grow clusters of hairs, called erineum, among which the mites live. On the underside of the leaf these galls have a shiny pale brown appearance. The galls are seen more often than the mite.

Other mites may cause an erineum (hairy patch) to form on Alder leaves

Gall Adult

Wherever Alder is found.

The galls are to be found when Alder is in leaf. They usually appear in June and reach full size in September or October.

Widespread, but under recorded in Britain.

Status in Leicestershire and Rutland not known.