Acari: Eriophyoidea - gall mite Phytoptus avellanae Hazel Big Bud Galls on Corylus avellana, Hazel Hosts: Corylus spp. It is thought there are probably two species causing bud galls on Hazel; Phytoptus avellanae forming galls over winter and the galls of Cecidophyopsis vermiformis developing in spring and early summer. However some authorities consider that Cecidophyes vermiformis is just an iniquiline of Phytoptus avellanae

Phytoptus avellanae
Studland Heath and Corfe Hills, Dorset. January and December 2018