Two lambswool sweaters go into the same drawer in April. In October one has a ragged hole the size of a pea near the left underarm, and the other, the same yarn from the same brand, is perfect. That looks like bad luck until you remember what happened to each one on its last day of wear. One went into storage straight off your back after a warm afternoon. The other went through the wash first.
Moths are not shopping your closet for the best fiber. The larvae are feeding on what you left behind, and the wool is simply what those traces are attached to. Once you follow that one detail, most of the standard advice about storage, cleaning, and rescue starts making sense in a different order.
The larvae eat, the adults only lay eggs
The small pale insect that flutters out when you open a wardrobe door cannot damage a single thread. Adult clothes moths do not feed at all. Their entire job is to mate and to place eggs somewhere dark and undisturbed. The University of Maryland Extension guidance states it directly: the adult moth does not feed, it reproduces. Every hole in a garment was chewed by a larva, often weeks or months before you noticed it.
That delay changes how you should read the sighting. A moth in flight is not the beginning of a problem, it is evidence that eggs may already be somewhere you are not looking: inside a seam, a folded cuff, the crease of a stored blanket, or under the edge of a wool rug. Swatting the one you can see resolves nothing about the generation you cannot.
Why body oils decide which sweater gets eaten
Larvae can digest keratin, the protein in wool, silk, feathers, and fur, which almost no other household insect manages. A 2020 paper in the journal Microorganisms, Larvae of the Clothing Moth Tineola bisselliella Maintain Gut Bacteria that Secrete Enzyme Cocktails to Facilitate the Digestion of Keratin, traced that ability to symbiotic bacteria in the larval gut that release enzymes capable of breaking the sulfur bonds holding keratin together.
Being able to eat wool is not the same as living well on it. Extension guidance notes that soiled woolens are the primary food, and that larvae struggle on clean wool because it lacks nutrients they get from stains and body residue. Sweat salts, skin oils, food spots, and drink spills supply the missing part of the diet. This is also why cotton and polyester are rarely touched unless they are blended with wool or heavily soiled.
So the hole near the underarm is not a coincidence of geometry. Underarms, collars, cuffs, and the seat of trousers are where residue concentrates, and residue is what a female moth is selecting for when she chooses a place to lay. A garment worn once and put away dirty is a marked target. The identical garment washed before storage is close to inedible.
What a national trap survey found in ordinary homes
This is a common household problem rather than a museum curiosity. English Heritage launched Operation Clothes Moth in April 2017, after its conservators recorded webbing clothes moth counts roughly doubling across five years in the historic properties they care for. Visitors took free pheromone traps home and reported what they caught, and results came back from 42 English counties.
Catches averaged around 17 webbing clothes moths per trap, higher in London and the south east, and higher in pre-1950 buildings and flats than in newer houses. Older buildings offer more voids and quiet corners, and shared walls give the insects routes between homes.
Where a closet hides the damage
Larvae avoid light and movement, which is why the damage rarely appears where you would look first. Clothes in daily rotation get shaken out constantly and are poor habitat. The pieces at risk are the ones that sit still: off-season knitwear, a stored suit, a folded blanket, a wool rug under a heavy sofa, felt in an instrument case.
Inside a garment, check the parts that never see daylight. Under collars and inside cuffs, along inner seams and waistbands, in the folds of anything packed flat, and in pockets where crumbs collect. On rugs, look at the underside and the strip that runs beneath furniture. A small tube of silk webbing with grit stuck to it, or a scattering of sandy specks, is more reliable evidence than a hole.
What each treatment actually kills
The methods people reach for do very different jobs, and mixing them up is how an infestation survives a cleanout. Some kill every life stage, some only remove adults, and some do nothing but tell you the insects are present.
| Method | What it does | Limits |
|---|---|---|
| Hot laundering | Kills eggs and larvae on washable items and removes the residue that attracts them. | Only for garments the care label allows; wool needs the right cycle and water temperature. |
| Dry cleaning | Kills all life stages present in the garment. | Gives no protection against a fresh infestation once the piece is back in the closet. |
| Freezing | Kills all stages if the temperature is low enough for long enough. | A home freezer is slower than most advice admits; see the timings below. |
| Vacuuming | Physically removes eggs, larvae, and debris from rugs, closet floors, and cracks. | Needs to reach under furniture and along edges, and the bag should go straight outside. |
| Pheromone traps | Catches adult males and shows you whether activity is rising or falling. | A monitoring tool, not a treatment; it will not stop larvae already feeding. |
The freezing timings are where most household advice goes wrong. The Museum Pests low temperature treatment guidance calls for a minimum of 72 hours at minus 30 degrees Celsius, and a minimum of 14 days in a domestic freezer running near minus 20. Since a kitchen freezer typically sits around minus 18, a weekend in a bag is not a treatment. Seal the item in strong plastic before it goes in, run one cycle rather than several, and let it come back to room temperature still wrapped, for at least 24 hours, so condensation forms on the bag instead of the wool.
Cedar blocks are not a plan
Cedar and lavender are the most popular defenses and the least effective. Cedar oil loses its strength within months, and a closet or chest cannot hold the vapor concentration that would actually repel an insect. Extension guidance is blunt about cedar closets and chests: the seal is not tight enough to keep a lethal or repellent concentration in the air.
Naphthalene mothballs do work as a fumigant, but only inside a genuinely sealed container, and they bring their own handling and toxicity concerns. Nothing sold as a scented deterrent substitutes for the two steps that break the cycle: clean the garment before it rests, and store it where an adult cannot reach it to lay.
A wool-season storage routine that ends the cycle
Do the work once a year, at the point where wool goes out of rotation. Wash or dry clean every wool and silk piece before it is put away, even the ones that look clean, because the residue you cannot see is the part that matters. Let everything dry fully, then pack it into a sealed box or a zipped bag rather than an open shelf or a garment bag with gaps.
While the shelves are empty, vacuum the closet floor, the corners, and the edge of any wool rug in the room, then put the vacuum bag in an outdoor bin. Hang one pheromone trap and write the date on it, so next spring you have a count instead of a guess. When the box comes out in autumn, shake each piece in daylight and check the collar and underarms before it goes back on a hanger.
The sweater that survived the summer was not luckier than the one with the hole. It was washed first, and that is the whole difference between a closet that feeds a generation of larvae and one that starves them.