The fly Urophora jaceana has a larva that produces galls on the flower heads of Common Knapweed which incorporates the receptacle and achenes. The gall is hard and woody; usually affecting most of the flower head; usually with several chambers, each with one larva.
Wherever Common Knapweed is found.
Galls from August to April, or puparium May and June (in old flower head).
Widespread and fairly frequent in Britain.
Probably fairly frequent in Leicestershire and Rutland but not well recorded.
Leicestershire & Rutland Map
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