Rags and sweaters alert! Are humans powerless against moths that eat sweaters?

Leviathan Press:

It’s hard to have a favorable opinion of these moths, considering they once ate through a favorite rug of mine. The only way to deal with these little moths was to use mothballs, but that didn’t help much. And you have to admit that the moths are perfect family companions, and their evolution is so unique and their will to survive is so tenacious that humans have so far failed to effectively deal with their invasion.

Every year, around the end of March, my family starts planning a massacre. Our target is the Clothes Moths in our home: we place pheromone traps in our closets, living room, and bedroom; we and our two cats are always on the lookout for any brown spots on the walls. Once we find a moth, we do everything we can to kill it. After killing so many moths, my husband and I can now even catch a flying moth directly from the air with our bare hands. But all this is not enough to eliminate the moths.

These particular moths are so well adapted to modern human life[1]; as a species, “they don’t actually live outside anymore,” Isabel Novick, a biologist at Boston University, told me. Clothes moths have evolved into a perfect annoyance, surviving on the objects in our homes to the point where getting rid of them permanently is nearly impossible.

Damage to clothing caused by the moth. © University of Georgia Archive, University of Georgia

Adult moths, at least, are easy to deal with. Their bodies are the size of fennel seeds and are fragile. Although they have wings, they are poor flyers—female moths prefer to crawl—and when they do manage to fly, they flutter and sway. The adults aren’t the problem, though; they don’t even have mouths. The real problem is the larvae, which make their homes in our closets and chew through hundreds of dollars’ worth of wool sweaters and cashmere cardigans.

Curtain moth larvae. © wikipedia

These moths belong to the order Lepidoptera—which includes butterflies and moths—and have been around for hundreds of millions of years, long before us, let alone our taste for luxurious outerwear. The larvae aren’t specifically targeting sweaters, though; they’re seeking keratin, a tough protein found in fur, feathers, horns, claws, hooves, and other animal appendages. Keratin is so tough that most animals have trouble digesting it and so avoid it. Yet, as Novick and other researchers have discovered, moths and their relatives have managed to evolve a way to take advantage of this opportunity.

In their larval state, these moths produce enzymes and digestive juices that help them break down keratin; they also appear to have gut microbes that dissolve materials that the animal’s body can’t.[2][3] For some species, this means feeding on horns, hooves, or hawksbill turtles. Other species, however, including the two species most commonly found in human homes, are not so picky about where their keratin comes from. That’s unfortunate for us, because the protein is ubiquitous in the average household, Dong-Hwan Choe, an entomologist at the University of California, Riverside, told me.

Larvae feed on wool. © Clemson University

Woolen clothing is a particular favorite of moth caterpillars. However, the caterpillars will also happily eat carpets and blankets made from animal hair, as well as downy furniture, wool insulation, the down stuffing in sofas and pillows, and even the wool felt pads sometimes found in pianos.[4]

In extreme cases, moths may also turn to nylon stockings, cotton blends, soybean meal, or household dust. These moths are considered a scourge in museums, where they will chew on specimens and precious artifacts; researchers have even found that moths will survive on mummified human remains.[5]

Novick told me that even if you don’t offer these pests clothing, they can still survive in your home. In my house, part of the strategy is defensive: We wash wool products regularly, don’t want to attract moths with body perfume, and seal our most precious clothes in airtight containers. But it’s futile to try to make any home completely keratin-free. This substance is found in our nails, hair, and the outermost layer of our skin. Although our two cats are skilled moth hunters, their hair accumulates in corners, furniture, and brushes, seemingly perpetuating our home’s pest population.

Novick, who lives with her cat, Valentine, has a similar dilemma, and she notes that in her situation, even more extreme measures, like hiring a professional to fumigate her room, would probably be futile — the moths would likely crawl back in from elsewhere in the building.

Adult of the curtain moth. © Wikipedia

In reality, many moth infestations end up being “more about management than eradication,” Choi told me, requiring frequent vacuuming, trapping, and scrubbing or dry-cleaning (or freezing, or even tumble-drying) of clothing to keep the pests under control. This is undoubtedly a huge time and financial investment. (Chemical interventions, such as mothballs and pesticides, can help but may not be a good option for people with pets, small children, or certain medical conditions; cedar boxes, on the other hand, seem like a dubious solution.)

Cui told me that while he often gets inquiries from people who are troubled by the pests, he can’t confirm that anyone has successfully eradicated them. Few solutions can tackle all of the moths’ evolutionary tricks . Novick points out that the moths have a high tolerance for inbreeding.[6] They can safely swallow mercury and lead, and are very tolerant of cold. Their eggs can survive being frozen for several days; when temperatures are cooler, the larvae can survive in their immature state for more than two years.

At the same time, heat increases their reproductive potential—and Novick worries that as climate change raises average temperatures, moth invasions (like many other indoor pest problems) may become more frequent. Novick tries to make the most of her own moth invasions: Her lab populations come from individuals captured in her own home.

It’s an admission that reconciliation and coexistence are the only way forward, just as fruit flies are accepted as an inevitable consequence of compost piles and cockroaches as a liability of city life. Perhaps these moths should be added to the list of pests to which we are forced to acknowledge a degree of defeat — or at least, to show grudging respect for their fragile but remarkably adaptable bodies.

By Katherine J. Wu

Tempura

Proofreading/Rabbit's Light Footsteps

This article is based on the Creative Commons License (BY-NC) and is published by Tempura on Leviathan

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