Species account from Moths of Glamorgan
(Gilmore, Slade & Stewart, 2009):

Univoltine, flying from mid May to August where bedstraw, willowherb or Fuchsia occur. Adults come to light, sometimes in large numbers with the best count being of 70 at Gowerton in July 1983. This is the commonest hawk-moth in Glamorgan, and its larvae are often encountered by members of the public in their gardens.