The Saturnia pavonia, commonly known as the small emperor moth, is an insect species known for its striking appearance and unique life cycle. This moth is a day-flying species, particularly the males, making it a visible inhabitant of various European and Asian landscapes. It represents the only resident member of the Saturniidae family found in the British Isles, a group otherwise known for the tropical silk moths.
Identifying the Small Emperor Moth
Adult small emperor moths possess distinctive physical characteristics. Their wingspan typically ranges from 40 to 60 millimeters, though some can reach around 80 millimeters. Both the forewings and hindwings feature prominent “eyespots,” which are large, circular markings resembling eyes, serving as a defense mechanism against predators.
Males and females display clear differences, showing sexual dimorphism. Male moths are generally smaller and exhibit bright orange hindwings, while females have a more subdued, greyer coloration on their wings. Males are active flyers during the day, aided by their feathery antennae, which are specialized for detecting pheromones released by females. Conversely, females typically fly at night, relying on their scent to attract mates.
From Egg to Adult
The life cycle of the small emperor moth begins with eggs laid singly or in loose clusters on the host plants. These eggs hatch within about ten days. Upon hatching, the larvae, or caterpillars, are voracious feeders and grow rapidly. Initially black and hairy, they undergo several molts, changing color to green with black hoops and yellow wart-like spots as they grow, reaching a length of approximately 60 millimeters. Their primary food sources include heather, sallow, hawthorn, blackthorn, and bramble.
After about six weeks of feeding, fully grown caterpillars prepare for the pupal stage. They spin a characteristic pear-shaped cocoon, typically brown and often concealed near the ground or leaf litter. This cocoon has a unique structure that allows the emerging moth to exit while preventing parasitic insects from entering. The pupa overwinters inside this cocoon, with the adult moths emerging in a single generation between April and May of the following year. The adult moths have a short lifespan, lasting only about three to four weeks, during which their primary purpose is reproduction, as they do not feed in their adult stage.
Where They Live
The small emperor moth inhabits various open habitats across its geographical range. These environments include heather moorland, heathland, open woodland edges, and scrubland. The species is particularly common in nutrient-poor grasslands with blackthorn scrub or hedges, as well as on larger woodland clearings and fens.
Its distribution extends widely across Europe and into more northerly parts of Asia, including throughout the British Isles. While adaptable to varied habitats, the presence of its specific food plants, such as heather and sallow, is a significant environmental requirement for its survival and population stability.