Emperor Moth

The emperor moth is a member of the family Saturniidae, the giant silk moths, and is the only representative of this spectacular family found in much of northern and western Europe. Its four prominent eyespots, one on each wing, make it instantly recognizable and give the family its common association with dramatic, eye-catching wing patterns.

The species shows unusually strong sexual dimorphism for a moth: males are smaller, more vividly orange-brown, and fly actively during the day searching for mates by detecting female pheromones with their large, feathery antennae, while females are larger, paler grey, and fly mainly at night. This day-flying behavior in males is relatively unusual among moths, most of which are strictly nocturnal.

• Wingspan of roughly 50–80 mm, with females noticeably larger than males, up to about 80 mm versus around 65 mm for males.
• Each of the four wings bears a large, dark eyespot with concentric rings, a hallmark of the species.
• Males are orange-brown with pinkish hindwing tones and broad, comb-like (pectinate) antennae used to detect female scent.
• Females are larger and more subdued in color, mostly pale grey with faint brownish markings and narrower antennae.
• Distinguished from other silk moths by its combination of four bold eyespots and strong day-flying male behavior.

Widespread across Europe into temperate Asia, favoring open habitats such as heathland, moorland, scrubby grassland, and hedgerows. Males fly actively by day in spring searching for females, while females typically remain still by day and fly at dusk or after dark to lay eggs. The flight period generally runs through spring into early summer.

Males use their large feathery antennae to detect pheromones released by females from considerable distances, flying rapidly and directly across open country during daylight in search of a mate. Females spend much of the day resting motionless, relying on cryptic coloration for camouflage, and become active mainly around dusk to disperse and lay eggs. Caterpillars feed on a range of shrubs and trees including heather, bramble, and hawthorn, and their prominent eyespot pattern in the adult is thought to startle or deter predators such as birds.

Eggs are laid in small clusters on host plant twigs and hatch into caterpillars that begin dark and gradually develop bright green coloring with black bands and yellow or pink wart-like tubercles as they mature. After several instars, the caterpillar spins a distinctive flask-shaped silken cocoon with a one-way entrance that allows the adult to emerge but prevents predators from entering. The species overwinters as a pupa within this cocoon, with adults emerging the following spring, typically producing one generation per year.