The mite Eriophyes laevis causes galls to form on the leaves of Alder (Alnus glutinosa). The galls start off shiny yellow, becoming green then red, purplish or brown. They are scattered over the leaf, often numerous, and with a small opening below. The gall is seen more often than the mite.

Aceria nalepai also causes galls on alder leaves, but in the axils of midrib/veins.  However, indeterminate examples can be found, and combinations of the galls are common.  

Gall Adult

State host, and provide a photo

On Alder

The gall can be seen at any time that Alder is in leaf, best time is around August and September.

Widespread and fairly frequent in Britain.

Fairly frequent in Leicestershire and Rutland.