The mite Aceria tenella causes galls on the leaves of Hornbeam (Carpinus betulus).  The galls occurs as a smooth, shiny bulge on the upperside of the leaf in the angle between the veins. The hairy opening below contains mites. 

Gall  Adult

Adult: Unless identified by a recognised expert, a photo is required and the specimen should be examined with a microscope. In the comments box, state the key or ID method used and describe the size and identifying characters.

Galls can be found on Hornbeam leaves where that species occurs.

Galls can be seen when Hornbeam is in leaf.

Status in Britain is difficult to determine due to lack of records.

Status in Leicestershire and Rutland not known.