The male and female emperor moth are slightly different, though both have four eye spots on their wings which are used to intimidate potential predators. When under threat, the moths can vibrate their wings to give the impression of a four-eyed monster.
The male emperor moth is slightly smaller and more colourful than the female with orange hind wings (see photo). Female emperor moths are inactive during daylight hours but they emit a pheromone which attracts male moths. The males fly by day and pick up the female’s pheromone using their large feathery antennae, it is thought that a male emperor moth can detect a female from up to seven miles away.
Their life expectancy as adult moths is extremely short since they cannot feed but if they find each other and mate their eggs will hatch in a couple of weeks and the tiny dark, spiny caterpillars will soon be on their way to starting the life cycle again.
Emperor moth caterpillars
The caterpillars feed on the leaves of woody plants, heather is one of their favourites but they eat a wide range of woody plants including hawthorn and blackthorn. They are most common on heathland but are also found in woodland and along hedgerows so they sometimes occur in gardens.
When fully grown in August, the caterpillar is the most easily-spotted stage in the life cycle of the emperor moth. At this stage the caterpillars are very large, maybe as a big as 6cm long, and they like to bask in obvious places. Not only are they big but they are also colourful, their vivid green background colour is complemented by black rings around their bodies which have yellow or sometimes pink spots within.
Around the end of August these large caterpillars crawl into an area of thick vegetation to pupate. Their first task is to spin a protective cocoon around themselves. These vary in colour from white to brown and are tough but papery and are attached to the vegetation.
Inside the cocoon the caterpillar pupates and it is in this form that it will survive the winter period. Nothing further happens until April of the following year when the adult moths begin to emerge from their cocoons.