The Vapourer Moth—Wingless Females and Hairy Caterpillars
The hairy caterpillars of the vapourer moth, Orgyia antiqua (Order: Lepidoptera; Family: Lymantriidae) are the prettiest that we've ever seen. They are also known as the rusty tussock moth. They are gray with red and yellow spots and carry four chimney-like tufts of cream-coloured hairs on their backs as well as two horn-like bundles of hair on their head and one at the rear end.
They live on many plants, such as rose, buddleia, rhododendron, hawthorn, apple. One should not pick them up or touch them with bare hands, as the hairs can cause irritation of the skin.
The female moths are wingless and look like brownish-grey sacks, whereas the males are fully winged and are orange-brown with a white spot on each forewing.
Biology of the Vapourer Moth
Caterpillars emerge from May onwards and feed until August-September. Female caterpillars feed some 10 days longer than males. Consequently, female caterpillars become much longer and can reach a length of up to 25 mm, compared to 15 mm for male caterpillars. Female and male pupae are, therefore, also different in size.
This is one of the few cases where sex can be established before the pupal stage.
The mature caterpillars spin a loose cocoon, often between leaves or on a twig, in which they process their body hairs. Inside the cocoon they pupate.
A few weeks later the adult moths appear, the males usually emerging earlier than the females.
The female stays near or on top of her cocoon and 'calls' males by emitting a volatile substance. After mating, the females produce 200-300 eggs on top of the cocoon. The females do not move away and probably die soon afterwards. The males die in autumn or winter, but the eggs - that have very hard shells - overwinter.
A Walking Caterpillar
Males are Extremely Good at Finding Females, as We Found Out.
One afternoon in August three vapourer moth males entered our flat through an open bedroom window, within one hour’s time. We captured the first two and released them, surprised why suddenly two identical moths had come inside, as we had never seen any of them in the neighbourhood, before. The third had made it all the way to the kitchen, and then we understood: the caterpillar that we had kept in a cage in the kitchen, and that had pupated a few weeks earlier, had just changed into a female vapourer moth - she must have been calling the males!
Damage by Orgyia antiqua
As mature caterpillars can eat quite a large amount of leaf, they can be troublesome in gardens. However, they seldom appear in large enough numbers to become a pest and if an outbreak is severe, it is always local.
Natural Enemies of the Vapourer Moth
The moths will undoubtedly be eaten by birds, spiders, and wasps of the Vespidae family. The latter are even known to 'steal' moths from spiders' webs.
Hairy caterpillars like those of O. antiqua, are usually avoided by birds, except for one bird that is specialised in hairy caterpillars: the cuckoo.
Other predators of caterpillars (hairy or not) are ground beetles (Order Coleoptera; Family: Carabidae), in particular, Calosoma sycophanta.
The caterpillars are also attacked by parasitoids, such as the wasps of the family Braconidae (Order: Hymenoptera) and tachinid flies (Order Diptera; Family: Tachinidae), whose larvae develop inside the caterpillar's body.
Treatment of the Vapourer Moth (Usually Unnecessary)
- If treatment is required, then remove the cocoons and eggs in winter. Wear cloves to avoid contact with the urticating hairs in the cocoons, as they can cause irritation of the skin!
- One could also try to attract tachinid flies and braconid wasps, by growing flat-topped open flowers, such as Compositae (e.g. daisies) or Umbelliphorae (e.g. dill).
© 2012 Marlies Vaz Nunes