Although I’ve named this blog post Rabdophaga rosaria, it is apparently difficult to be specific as to which exact species has caused galls like the one pictured below, so finds are recorded as Rabdophaga strobilina / rosaria agg. The gall causer is a midge, of the family Cecidomyiidae, of which there are more than 600 species in Britain. All are tiny, less than 5mm in length, and it is their larvae that cause the plants they inhabit to form galls. In this instance, the galls are formed in the buds of willow species.