A univoltine species: mid April (sometimes earlier) to late June or early July, the long flight period resulting from the staggered emergences of individuals parasitizing different hosts. In Ireland, Stelfox (1927) reports that the species is occasionally observed on the wing as late as August or September, the females appearing to linger long after all possible hosts have vanished. He considers that these late specimens may be due to the emergence of a partial second brood, unknown in Britain. Bossert (2014) reports flight activity in August at 2000m altitude in the Austrian Tyrol.