They’re common, and widespread, and some species may be up to 15cm long – but some of these moths have never been seen as an adult, because they never leave their protective case. Would you be able to recognise a case moth?
Common name: Case Moth, Bagworm Moth
Scientific name(s): Family Psychidae – over 1300 known species worldwide, and 350 in Australia.
Description: Case moth caterpillars spend their life inside a sleeping-bag-like case, spun from brown or grey silk and decorated with twigs, debris, or dead leaves. Some common species can be recognised by the shape and decoration of the case. In some species, the head and first few body segments of the caterpillar may be orange and black, visible when the caterpillar is feeding. The cases have an opening at the head and tail end, but these are held shut unless the caterpillar is feeding or excreting.
They will pupate inside the case and emerge from the lower end of the case as an adult moth. Adult case moths are generally dark brown in colour with pale stripes or spots, or mottled, although some have clear wings with hairy bodies. In some species the wingless females will never leave, mating and laying her eggs inside the case after pupation. Some species can produce fertile eggs without mating, and in one species the newly hatched caterpillars will eat their way out of the mother’s body.
Geographic distribution: Worldwide. Some species have spread far from their original range, but the common species in Australia are all native.
Habitat: Case moth caterpillars will drag their protective case around the food plant, tree trunk, or rock surface, and when ready to pupate will permanently attach one end to the surface with silk and hang there. The various species have exploited a wide range of habitats and plants species and the cases they make will reflect the plants on which they feed.
Pest status: Newly hatched caterpillars, wearing their first tiny silk cases, may appear in large numbers as they disperse seeking suitable food plants. Older case moth caterpillars can defoliate small garden plants, and when ready to pupate may climb the windows and outside walls of houses, seeking a good spot to suspend themselves. They may also be mistaken for the cases of the much smaller case-making clothes moth and plaster bagworms, (Family Tineidae), but true case moths are very unlikely to be found inside the house.
Treatment: Case moth caterpillars may be sprayed with contact insecticides like bifenthrin, but since they are unlikely to reach plague numbers in Australia, physical removal of the caterpillars from the host plant, or from the walls of buildings, is more effective where desired.
Daniel Heald, technician and entomologist