Bagworm Moth, Bagworm Moths, Bagworm, Bagworms, Bagmoths
Psychidae is a family of moths from the Lepidopteran insect order. They're a small and peculiar group, comprising only 1,350 species. Their larval behaviour is unique, where a caterpillar collects items from its surroundings, creating a protective, well-camouflaged structure that conceals them as they go about their day. Most species in the family are harmless to garden plants, mainly eating fungi, dead insects, mosses, lichens and decaying leaves. Few species are severe pests of Wattle and Orange in the Americas, who attack the new growth of plants. Interestingly, the female moths' and fly look similar to fly larvae, and research has shown that eggs survive throughout the birds intestine. This suggests these insects depend heavily on birds for dispersal.
Adult: Variable in size, the largest species is roughly 1.5-2cm long (wing length: 3-15mm), with the hindwing width equal to the forewing in males. Observers rarely see the adult moths because they're either short-lived or stay concealed by their handmade cases. The females are wingless and described as maggot-like. The males possess translucent wings covered in fine, fuzzy hair, which are the wing scales. The bodies are typically dark coloured and the antennae feather-like. Moths in this group are identified using the larval casings.
There is a handful of species that may cause havoc in the garden, but they really only make up a small fraction of the group. Many feed on things like lichen and decaying leaves, so it's likely they play an important role in the food web. If you suspect an infestation of a pest insect, the best way to get rid of them is by removing cases by hand and squashing the caterpillar inside. Dispose of insects in the general waste, never put them in compost or food waste bins as this can result in reinfestations.
Unfortunately, chemical treatments are ineffective because these insects often reside in large trees. Contact insecticides probably won't do anything because they are protected in their purpose-built cases.