A large, strong-flying butterfly restricted to the Norfolk Broads, although migrants are occasionally seen elsewhere. Pale yellow wings with black veins and blue margins.

This is one of our rarest and most spectacular butterflies. The British race britannicus is a specialist of wet fenland and is currently restricted to the Norfolk Broads. Here the adults can be seen flying powerfully over open fen vegetation, stopping to feed on flowers such as thistles and Ragged-Robin.

This species can be quite distinctive although it is also very variable in its colouring. The forewings have three cross-lines; a high cross-line curving around a white spot, a central scalloped cross-line and a lower cross-line which is irregular and jagged. The wings can be predominantly warm reddish-brown but also commonly with areas of grey and brown.

The adults are incapable of feeding. They fly at night and are attracted to light. In mainland Europe they overwinter as part-grown larvae on the ground among fallen tree needles or moss.

This species is easily identified by the protruding snout and unusual resting wing posture where the hind wings protruding in front of the forewings. There is little variation in the colouration except for rare pale or black forms.

The adults are incapable of feeding. They fly at night and are attracted to light in small numbers. The caterpillars can be found from August to late the following May, feeding at night and overwintering a small larvae. They pupate in a tough cocoon on the ground.

One of only three species of this family that are found in the British Isles.

The adults are incapable of feeding. The caterpillars live inside the trunks of a variety of broadleaved trees feeding on the wood. They overwinter three or four times as larvae and a final time as pupae.

The wings are a pale yellow colour which fades whiter with age, with two darker lines crossing the forewings and one line crossing the hindwings.

The adults are occasionally disturbed during the day but they are strictly nocturnal flying rapidly at night. They are attracted to light. They overwinter as caterpillars in a bark crevice.

The grey forewings are crossed by jagged cross-lines and bands. The red hindwing which gives it the English name has a black band around the scalloped margin, fringed with white. Another irregular black band runs across the centre of the red patch of the hindwing.

The larvae can be found from May to July feeding at night and hiding under loose bark or in a crevice during the day. They overwinter as eggs.

The usual form in rural areas is all white peppered with black dots on both the wings and body. Black forms known as f. carbonaria were once dominant in industrial areas with high levels of pollution although their frequency has been steadily declining in recent years. Intermediate forms known collectively as f. insularia are variable between the light and dark forms.

The larvae can be seen between early July and late September before they overwinter as pupae just below the ground.

Size and Family

The females are much larger than the males, but both rest with distinctive forward-facing furry legs. The markings are usually darker and more extensive in the males, which also have feathered orange-brown antennae. The males often come to light in larger numbers than the females.

The larvae are a bright greenish-yellow, with four tufts of golden yellow hairs. They grow slowly between late June and early October, then overwinter as pupae.

Distinguished from other large eggar moths by the diagonal cross line on the forewing and two small white spots. Males are usually a warm reddish-brown with yellowish patches. The females are larger and can vary in colour from deep yellow to a very pale buff, whitish or a darker reddish-brown similar to the male. In the fens of East Anglia the males are often yellowish.

When at rest, the wings are held almost vertically against the body with two buff areas at the front of the thorax and at the tips of the forewings which look very like the pale wood of the birch. The rest of the wings are the same mottled grey colour of the birch bark.

Occasionally the adults can be found resting in the day on a twig or the ground. They fly at night and comes to light, usually after midnight.

The yellow and black caterpillars can be seen from July to early October before they overwinter as pupae under the ground.

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