To get a sense of how tiny this moth is, it’s sitting on my window screen. The whole moth is perhaps 3mm long.
The casemaking clothes moth gets its common name from its behavior — its larvae, which look like regular caterpillars, form flattened cases for themselves out of whatever’s handy, and primarily eat fibrous keratin, such as hairs, feathers, carpets, fur, upholstery and wool. (On the bright side, they also consume spiderwebs, detritus, and unused bird nests.) The Latin name, Tinea pellionellus, comes from tinea, the generic term for micromoths (it would please me so much to know that it’s pronounced “tiny-ah”, but I suspect it’s “tin-eh-ah”), and the Latin word for furrier, pellionellus.
The cases the caterpillars live in protect them not only from predators, but also from water loss. In an environment with reduced humidity, the case will lose water before the caterpillar, and the caterpillar itself will lose water more slowly than one that is not in a case. In very high humidity (looking at you, Florida!), the case can actually become full of water and quite heavy, and the larva will leave the case and make a new one. Larva can even eat the case in an emergency.
A common pest often found indoors near humans, T. pellionella was among the first moths to be scientifically described in any sort of modern way.