Because they migrate annually from southern Europe and north Africa, the numbers of the Clouded Yellow butterfly, Colias croceus, present in the UK vary between years but, although infrequently, they may arrive in such large numbers there are memorable ‘Clouded Yellow Years’. They are, however, regular visitors to Hampshire and the Isle of Wight, with the first arriving in late May or early June. Many Clouded Yellow butterflies remain near the coast where they feed, mate and lay eggs, while small numbers may then disperse inland.
Eggs are usually laid on clover or lucerne leaves. After hatching, and depending on temperature and sunshine, the larvae take between 20 and 40 days before they pupate. The pupal stage lasts about 18 days. Although larvae, like pupae, have been recorded as overwintering in the south of England, many would be killed by the damp and frost leaving any survivors to emerge as adults in early spring. The adult butterfly feeds on nectar from knapweeds, clovers, dandelions and many of the other grassland flowers.
The upperside of the wings - bright yellow and bordered by dark edges – are only seen when the adult is in flight. The Clouded Yellow always settles with wings closed at rest so exposing the yellow hindwings with two silvery-white spots.
