It was impossible to miss the rusty tussock moth (Orgyia antiqua) caterpillar foraging on my raspberry bush. Its body was dotted with orangey-red pinacula, wart-like growths sprouting clusters of pale lemon hairs. It had two bristly black antler-like protrusions at the front of its head, and a tail-like projection from its rear. Along its back four sulphur-yellow dorsal tufts stood proud, like the bristles of an interdental toothbrush. Measuring it at 25mm in length, I could tell it was a female, as males reach a maximum of about 15mm.
These caterpillars are polyphagous, feeding on a wide range of deciduous trees and shrubs, so I potted up a selection of raspberry, blueberry, hazel and birch, and introduced her to a rearing cage. After five days of feasting, she stopped eating and spun a cocoon on the underside of a hazel leaf. Over the course of a week I squinted through the web of silken threads, watching the silhouette of her larval body melting and morphing into adult form.
It was a russet-coloured moth fluttering at the mesh one evening that alerted me to her emergence. Males can detect a female’s pheromones from several miles away and it is these alluring “vapours” that give the species its other common name, vapourer.
My boldly coloured caterpillar had transformed into a muted greyish-beige moth with a plump, segmented body and epaulette-like vestigial wings that rendered her flightless. But her suitor was undeterred by her drab appearance. As soon as I unzipped the cage he alighted beside her and they began to mate. Fifteen minutes later, the male departed and, gravid with fertilised eggs, she began ovipositing.
The next morning I woke to find the exterior of the pupal cocoon bestudded with ova. The average batch size is about 300 eggs, but I counted 583. Each cream-coloured sphere was 0.75mm in diameter and had a darker beige ring below its dimpled top, like a tiny, upturned button mushroom.
Females usually die soon after laying, and the larvae may not hatch until next spring, but 10 days on she was still clinging to her cocoon, surrounded by the promise of her future progeny.
