Chirosia betuleti

Alternative names
Mop-head gall

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.

Identification difficulty

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

When to see it

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

Life History

How the fly passes the winter appears to be unknown.

UK Status

Widespread and fairly frequent in Britain.

VC55 Status

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

Leicestershire & Rutland Map


Yellow squares = NBN records (all known data)
Coloured circles = NatureSpot records: 2020+ | 2015-2019 | pre-2015

UK Map