Sweater-Eating Moths Are an Unbeatable Enemy

Every year, beginning around the end of March, my household starts planning a massacre. Our targets are our home’s clothes moths: My spouse and I lay pheromone-laced traps in the closets, living room, and bedrooms; we—and our two cats—go on alert for any stray speckle of brown on a cream-colored wall. The moment we spy an insect, we’ll do whatever we can to crush it. After killing dozens upon dozens, my husband and I can now snatch moths straight out of the air.

None of this has been enough to eliminate the moths. These particular moths—webbing clothes moths—are simply too well adapted to modern human life; as a species, “they don’t really live outside anymore,” Isabel Novick, a biologist at Boston University, told me. Clothes moths have evolved into a perfect nuisance, so capable of subsisting on the contents of our homes that permanently purging them may be impossible.

Adult clothes moths, at least, are easy game. Their bodies, the size of fennel seeds, are fragile. And although they have wings, they’re poor flyers—females prefer to walk—and when they do force themselves aloft, manage only weak lurches and lilts. The adults, though, aren’t the problem; they don’t even have mouths. The larvae are the ones that post up in our closets and chew their way through hundreds of dollars of woolen sweaters and cashmere cardigans.

These moths belong to a group of insects—Lepidoptera, the order that includes butterflies and moths—that’s been around for hundreds of millions of years, well predating us, much less our taste for luxe outerwear. What the larvae are after, though, is not sweater-specific; they’re hungry for keratin, a hardy protein found in fur, feathers, horns, claws, hooves, and other animal adornments. Keratin is tough enough that most animals find it quite hard to digest, and leave it alone.

Clothes moths and their relatives, though, managed to evolve a way to capitalize on that opportunity, as Novick and other researchers have found. In their larval state, the moths manufacture enzymes and digestive juices that may help them break down keratin; they also appear to host gut microbes that dissolve substances that animal bodies cannot. For some species, that means feeding on horns, hooves, or tortoiseshells. Others, though, including the two clothes-moth species most commonly found in human homes, are far less picky about where their keratin comes from. Which is unfortunate for us, because the average home is full of the protein, Dong-Hwan Choe, an entomologist at UC Riverside, told me.

Woolen clothing makes for an especially convenient meal. But clothes-moth larvae will also happily eat carpets and rugs woven with animal hair—as well as upholstered furniture, wool insulation, the downy stuffing in couches and pillows, and the woolen felt pads sometimes found in pianos. Pushed to its limit, webbing clothes moths may also turn to nylon stockings, cotton blends, soybean meal, or household dust. The moths are considered a scourge in museums, where they’ll eat their way through taxidermy and precious artifacts; researchers have uncovered clothes moths subsisting on mummified human remains. Starve the pests of clothes, and “they can still live in your house,” Novick told me.

In mine, part of our strategy is defensive: We clean our woolens frequently, not wanting to attract the moths with the parfum of BO, and seal away our most precious clothes in airtight containers. But trying to keep any home keratin-free is a pointless exercise. The substance is in our fingernails, our hair, the outermost layer of our skin. And although our cats, Calvin and Hobbes, are adept moth-hunters, their fur—which accumulates in corners, on furniture, and on brushes—seems to be keeping the pest population in our home alive and well. Novick, who shares her apartment with a cat named Valentine, is in a similar bind. She also points out that, in her particular living situation, even a more drastic measure, like hiring professionals to fumigate her unit, would likely be futile. The moths would probably come creeping back from elsewhere in the building.

Realistically, many clothes-moth invasions end in something “more like management than eradication,” Choe told me, requiring frequent bouts of vacuuming, trap-laying, scrubbing, and laundering or dry cleaning (or freezing, or even baking) clothes to keep the pests at bay. It’s a huge time investment, and potentially a steep financial one, too. (Chemical interventions, such as mothballs and pesticides, can help, but may not be great options for people with pets, small kids, or certain medical conditions; cedar chests, unfortunately, seem to be dubious solutions at best.) Choe told me that, although he’s frequently consulted by people with infestations, he can’t say for sure whether any of those individuals have successfully trounced the pests.

And few solutions can solve for all of the moths’ evolutionary tricks. Clothes moths have a high tolerance for inbreeding, according to Novick. They can safely swallow mercury and lead and are quite cold resistant. Their eggs can withstand freezing for several days; when temperatures are cool, larvae can persist in their immature state for more than two years. Heat, meanwhile, bumps up their reproductive potential—and Novick worries that, as climate change raises average temperatures, clothes-moth infestations, like many other indoor pest problems, could rise in frequency.

Novick has tried to make the best of her own clothes-moth infestation: She started her lab colony from individuals she captured in her own home. It’s a kind of admission that coexistence is the only path forward, in the same way that people accept fruit flies as an inevitability of compost piles, and cockroaches as a tax of urban living. Perhaps these moths should be added to the pantheon of pests to which we’ve been forced to concede a degree of defeat—or, at the very least, grudging respect, for how scrappy their brittle, brilliantly well adapted bodies are.