Galls on creeping thistles

Galls on creeping thistles

Observation - Galls on creeping thistles - UK and Ireland. Description: The stems of a number of creeping thistles (Cirsium arvense) had hard swellings - none of these had flowers. We were raking up mowings, including one plant with one of these galls. Cut open, it contained a white grub, The gall causer is a picture-winged f

The stems of a number of creeping thistles (Cirsium arvense) had hard swellings - none of these had flowers. We were raking up mowings, including one plant with one of these galls. Cut open, it contained a white grub, The gall causer is a picture-winged fly.