Emperor Moth

Daytime flight

The emperor moth is unusual among British moths in being partly diurnal — males fly in bright sunshine in April and May, searching for females. They fly low over heathland in rapid, erratic zigzag patterns, following invisible chemical trails. The two sexes differ dramatically: males are smaller with russet-orange hindwings and fly by day; females are larger, grey-buff, and fly at night. Both sexes have the four large eyespots.

Olfactory miracle

The male emperor moth’s antennae are feathery and enormously sensitive — they can detect a single molecule of the female’s sex pheromone and track its source from distances measured in kilometres. Experiments have recorded males locating caged females from over 11 km away under good conditions. The pheromone receptors on the male’s antennae are so specifically tuned that no other compound triggers the same response.

Caterpillar

The caterpillar is one of the most attractive in Britain — bright emerald green with black rings and yellow or orange spots, the spots bearing tufts of black hairs. It feeds on a wide range of plants including heather, bramble, meadowsweet, and blackthorn. Fully grown caterpillars pupate in a tough, pear-shaped silk cocoon attached to heather stems, in which the insect overwinters.

The silk

Emperor moth silk was historically used in small quantities — the cocoon contains a few metres of usable silk. The species is closely related to the domesticated silk moth (Bombyx mori) and to the larger wild silk moths of Asia (Antheraea species) whose silk was woven into tussah silk fabric. British emperor moth silk was never commercially significant but the cocoons were collected by Victorian naturalists.