The larvae of the Cynipid gall wasp Aulacidea hieracii gall the stems of Hieracium species. The galls are rounded swellings up to 4 cm long. The part of the plant above the gall is usually strongly suppressed. The gall may be smooth, but can also be covered by erect white hairs, it is green and succulent at first becoming hard and brown later. Each gall contains several chambers each containing a whitish larva or a pupa. 

It is a unisexual species, with males rare or absent; the females reproduce by parthenogenesis

Gall:

Photographs of the gall required.  Please state the host plant – i.e. Hieracium sp.

Wherever the host plants (Hieracium species) grow.

Galls: summer and autumn.

Univoltine, hibernation and pupation in the gall.

Widespread, but not well recorded in Britain.

Rarely recorded in Leicestershire and Rutland.