Single or possibly double brooded. The extensive set of records on the scheme database (300) indicate the moth flies from the end of May through to early September with a fairly steady build up in numbers to a peak in the first half of August. The couple of late September records are, perhaps significantly, from the mild climate of the Scilly Isles although there are no corresponding late records from the Channel Islands. Larval records received to date all relate to the period mid-March to the end of May suggestive of a single extended brood.
E. R. Bankes, in his 1894 paper in the Entomologist's Monthly Magazine (30:82), reported it as double brooded from June to July and again in August to September. The larval feeding periods were given as April to May and July to August, however he also noted he and W. H. B. Fletcher had only met with the first brood larvae and that it was solely Mr. Richardson's experience of regular second brood larvae he was quoting.
Earliest: 15th May 1997 (VC9) and 2016 (VC1).
Latest: 27th September 1957 (VC1)