The midge larvae of Rabdophaga strobilina / rosaria agg. cause a conspicuous rosette shaped gall to form in the terminal bud of various willows especially White Willow. Often more than 20 mm across the gall has a central chamber which contains a pink or red larva. The galls often remain on the host plant through winter. 

There are likely to be several similar species galling different Salix host species, but this is not yet established (ref. Redfern and Shirley (2011)

Gall (as species aggregate)  Adult

Please accurately identify the species of host plant in your comments; this may help to determine it to the species in the future.  See https://www.naturespot.org/family/salicaceae for guidanne on identifying willows and sallows.

On various Willow and Sallow species 

Late summer and early autumn.

Widespread and probably fairly frequent in Britain, but under recorded.

Seems to be becoming increasingly frequent in Leicestershire and Rutland. The gall recorded at Melton Country Park on 10th September 2014 is believed to be the first record for VC55.