Known as 'bagworms' or 'case-bearers', the larvae of the Psychidae construct cases out of silk and environmental materials such as sand, soil, lichen, or plant materials. These cases are attached to rocks, trees or fences while resting or during their pupa stage, but are otherwise mobile. The larvae of some species eat lichen, while others prefer green leaves. In many species, the adult females lack wings and are therefore difficult to identify accurately.
Each species makes a case particular to its species, making the case more useful to identify the species than the creature itself.
The family is fairly small, with about 800 species described, in Lithuania about 20 species.