Clouded Yellow Colias croceus (Geoffroy 1785)
Family: Pieridae, sub-group Coleadinae (the Yellows)
Photo by Paul Simmons
Photo by Robert Hulmes (same photo as header)
Only two species of yellow butterfly are likely in Yorkshire: Clouded Yellow and Brimstone. Both invariably perch with their wings closed. Brimstone’s prominent wing veins and leaf-like wing points are distinctive, whilst the Clouded Yellow’s figure-of-eight spot on the lower wing is characteristic. In flight the male Clouded Yellow’s rich mustard-yellow upperwings can be picked out, as can the female’s deep orange-yellow. By contrast, the Brimstone male is a bright, very noticeable, citrus yellow, whilst the female is a greenish-tinged white. Clouded Yellow males have solid black margins to all four upperwings. Females are similar, but the black margins are dotted with yellow spots. In bright sunlight these margins can be seen through the closed wings of a perched butterfly. Around 10% of female Clouded Yellows have pale, white to grey upperwings, instead of yellow, (the helice variety).
Clouded Yellows can turn up anywhere, but particularly favour wilder or more natural grassland areas including the margins of disused railway tracks and grassed-over quarries. Females will lay eggs singly on a wide range of pea family plants, notably Clovers, Bird’s-foot Trefoil Lotus corniculatus and Medicks especially the fodder crop Lucerne Medicago sativa. The species suffers at larval and pupal stages from excessively cold or wet weather, so is likely to remain only a very marginal resident in southern Britain in the foreseeable future. However, in good immigration years large numbers can reach Yorkshire and if this is as early as May or June, at least two generations are possible, given reasonable weather, with offspring typically appearing in July/Aug and Sept/Oct and even Oct/Nov.
Each new generation may head further north, giving rise to the possibility of offspring and new immigrants appearing together, but around late Aug/Sept onward there is an increasing tendency for a reverse southward migration to take place.
The Clouded Yellows is a periodic immigrant to Yorkshire from the Mediterranean area where it breeds more or less continuously, summer and winter. From late winter the species moves northward into central France. Occasionally individuals arrive in southern Britain in February, but more typically the first arrivals along the South Coast (and in Yorkshire) are in May and June.
It can turn up anywhere in Yorkshire, but more frequently on the southern half of the east coast or in south Yorkshire. Although not recorded every year, most years see one or two reports and numbers in Yorkshire are usually highest in the autumn.
Each female is capable of laying 600+ eggs, placed singly on the tops of the leaves of clovers, vetches and other pea family members. They are bottle-shaped, initially yellow-white, turning to pinkish orange and then to leaden grey the day before hatching, which is after 7-10 days. Most of the eggshell is eaten, then, for the first few days, the larvae feed on the cuticle of the leaves without perforating them. Later they strip the whole leaf. Larvae are dark green with yellow and orange streaks on each side, and short white hairs. The larval stage passes through 5 instars in three to six weeks (but may develop much more slowly in winter). The pupa is yellowy-green with a few black dots. It is attached by silk to the stems of food plants and the adult emerges after two to three weeks.
The species is not under threat. Numbers in Yorkshire have fluctuated widely. In 2000, 582 butterflies were seen. Since then, the maximum count was 150 in 2006 and the minimum was zero in 2010. However, it is widespread in Southern Europe and occasionally builds up huge populations, so the species is not regarded as Threatened.
Paul Simmons last updated date: 26/11/20