The clouded yellow butterfly: identification and migratory behaviour

The clouded yellow butterfly (Colias croceus) is a migrant species in the UK. Unable to survive the winter here, each spring it flies north from its breeding areas near the Mediterranean. In some years large numbers reach our shores, in others it can be completely absent.

Being a long-distance migrant, the clouded yellow has a strong flight. This large yellow butterfly might get mistaken for one of our other yellow British butterfly species, such as the brimstone, or even a white. When the clouded yellow is in flight we get a glimpse of the orange-yellow upperwing with its broad black margin but at rest it invariably closes its wings so we can see only its underside. Underneath the clouded yellow is deep yellow with a pair of silvery spots in the centre of the hindwing and a dark spot in the centre of the forewing.

Although a migrant, the clouded yellow does breed in the UK during the summer. Early migrants arrive in May and June, their young combined with later migrants can boost numbers significantly during August and a further brood can be seen on the wing during September and October.

Where to see clouded yellow butterflies

The best place to look for clouded yellows is along the south coast of England, particularly in flower-rich meadows where they pause to feed and possibly lay eggs on clovers and trefoils, but they can be seen across the length and breadth of the UK in any habitat, including gardens.

Attracting clouded yellow butterflies into the garden

Clouded yellows are wide ranging but are most commonly found in open countryside such as farmland and coastal cliffs. Clover and bird’s-foot can attract this bright yellow butterfly species into your garden.

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Clouded yellow butterfly life cycle

Egg laying time

Migrant clouded yellows arrive in late May and early June, laying their eggs in June. The pale yellow eggs are laid singly on the underside of food plants such as clover and bird’s foot trefoil, and hatch after about a week.

Clouded yellow butterfly caterpillars

The larva of clouded yellows are a rich grass green. As they develop they form a yellow stripe banded with orange along their side and very fine short white hairs. Growth can be variable, with the duration of the larval stage up to six weeks long in cooler summers, or three weeks when it’s warm.

Clouded yellow butterfly chrysalis

The pupa is a leafy green and will be attached to the underside of foodplants. It will remain in its chrysalis for two to three weeks.

Transformation into butterflies

In late summer there can be an abundance of clouded yellow, with some years being known as ‘clouded yellow years’. This is because the migrant numbers are swelled by the British-born butterflies, who emerge from their pupae from August onwards. The butterflies are quite large, with a wingspan of about 6cm. You can still see clouded yellows on the wing as late as early November.

Male and female clouded yellow butterflies

Females are slightly larger than male clouded yellows, and the black margins of their wings are speckled with yellow. The yellow and black markings make them one of the most striking yellow British butterflies.

Clouded yellow butterfly and hibernation

Like other migratory species, such as the red admiral, the British climate is generally too cold and damp for clouded yellow butterflies to successfully survive dormancy. It is the larvae from the second generation who attempt to overwinter, choosing coastal undercliffs to hibernate.

Find out more about wildlife gardening, including best plants for butterflies and tips for photographing butterflies

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