Vaporer Moth

The vaporer moth, also called the rusty tussock moth, belongs to the tussock moth subfamily (Lymantriinae) within the Erebidae, a group known for hairy, often colorful caterpillars and pronounced differences between the sexes. It is widespread across Europe, temperate Asia, and has been introduced to parts of North America.

This species is a textbook example of extreme sexual dimorphism among moths: males are fully winged, rusty-orange, and fly rapidly by day searching for mates, while females are almost entirely wingless, remaining stationary on or near their cocoon, resembling a small gray furry sac rather than a typical moth.

The species is ecologically notable both for this dramatic dimorphism and for its brightly tufted, hairy caterpillars, which are conspicuous on a wide range of trees and shrubs in parks, gardens, and woodland.

• Male: rusty orange-brown forewings with a small white spot near the trailing edge, feathery antennae, and a compact, fast, whirring day-flight.
• Female: wingless, gray, plump, and hairy, resembling a small furry grub rather than a moth; she stays on or near her cocoon after emerging.
• Caterpillar is boldly patterned with dense tufts of hair, including forward-pointing black 'pencil' tufts near the head, a pair of longer tufts near the tail, and a row of brush-like yellow or cream tussocks along the back.
• Distinguished from other tussock moths by the male's small size, orange coloring with a single white spot, and the female's near-total lack of wings.

Found across Europe, temperate Asia, and introduced populations in parts of North America, in a wide range of wooded and semi-wooded habitats including parks, gardens, hedgerows, orchards, and urban street trees. Males fly by day, especially in late summer and autumn, searching for the flightless females, which remain on tree bark, fences, or their own cocoons.

Males fly rapidly and erratically during the day in search of pheromone-releasing females, which are unable to fly and instead sit exposed on bark or other surfaces after emerging from their cocoon, mating and laying eggs in place. Caterpillars are generalist feeders on the foliage of many deciduous trees and shrubs, including birch, oak, hawthorn, and fruit trees, and their conspicuous hair tufts serve as a visual deterrent to some predators. The species can occur in large enough numbers on ornamental and fruit trees to be considered a garden pest in some years.

Females lay eggs in a mass on the outside of their cocoon rather than dispersing them, since they cannot fly to find new sites. The eggs overwinter and hatch into hairy caterpillars in spring, which feed and molt through several instars before spinning a cocoon incorporating their own body hairs. Adults emerge from the cocoon in summer to autumn; males fly off immediately while females stay put to mate and lay the next generation's eggs. There is typically one generation per year in cooler climates, sometimes two further south.