Considered to be single brooded in the Moths and Butterflies of Great Britain and Ireland Vol. 4 (2) and reported as flying during May and June. On the Recording Scheme database there are around 2100 records covering a flight period from late April to late September with peak emergence from mid-May to early August. The flight graph appears indicative of a species with an extended flight period rather than two separate broods but, intriguingly, most of the September records are from one site in London.
It is also reported as single brooded in northern Europe but there are reports that the larva has been noted in two generations (June-July and September), by inference, in southern Europe. The larva have only been reported in September and October in Britain.
Earliest: 22nd April - 1982 (VC8), 2007 (VC17) and 2011 (VC37)
Latest: 28th September 2011 (VC16)