Chirosia betuleti

Chirosia betuleti is a small grey fly resembling a small house fly. Its larvae cause galls to form on ferns, and in particular on Male-fern, Lady-fern and Buckler-ferns. Eggs are laid in the tip of the fronds, and the resulting larvae tunnel into the main stalk causing it to twist and the pinnae to become bunched and distorted like a mop head. Some of the pinnae may turn brown and die.

Gall Adult

Wherever the host plants are found, usually in damp shady places.

The gall can be found from early summer until late in the autumn.

How the fly passes the winter appears to be unknown.

Widespread and fairly frequent in Britain.

Little recorded, but probably fairly frequent in Leicestershire and Rutland.