The Clouded Yellow (Colias croceus) is primarily an immigrant to the UK, originating from North Africa and southern Europe, with numbers varying greatly from year to year. Each season, we normally see at least a few reaching our shores and, occasionally, they arrive in large numbers; such as the estimated 36,000 that appeared during 1947 when good numbers of much rarer migrants, such as Bath White (Pontia daplidice) and Pale Clouded Yellow (Colias hyale), were also recorded.
In more recent years, it has been shown that this species has successfully overwintered in the south of England. However, it is believed that the majority of individuals perish, since both larva and pupa of this continuously-brooded species are easily killed by damp and frosty conditions. In good seasons, C. croceus can produce up to three generations in the UK. In flight, the orange-yellow colour is quite distinctive, and unlike any other species. The pale helice form, occurring only in the female, is a creamy white, rather than yellow in colour and may lead to confusion with other similar species.
This strong-flying species always settles with its wings closed and so the dark borders on the uppersides of the wings are only clearly visible when in flight or when viewed backlit at rest. There is no elaborate courtship and, having mated, the female is subsequently able to lay an extraordinary number of eggs; up to 600 have been recorded from a single female.
Two females from 2013 above ...