Do Moths Eat Cotton Hoodies?

The bins come down in September. Somewhere in the second one is a hoodie you last wore in May, and on it is a hole the size of a match head. The word everybody reaches for is moths. Sometimes it is moths. On a cotton garment, more often it isn't, and the reason comes down to what the larvae can actually digest.

What clothes moth larvae eat

Clothes moth larvae feed on keratin, the protein in wool, fur, feathers, hair and silk. They are unusually good at it. A 2020 paper in Microorganisms by Vilcinskas and colleagues looked at how Tineola bisselliella manages a diet most animals can't touch, and found the larvae carry gut bacteria that secrete keratin-degrading enzymes, including one that breaks the disulfide bonds holding the protein together. The paper is about feathers and wool. It says nothing about cellulose, which is worth stating plainly rather than dressing up as proof of anything.

Cotton is cellulose. There is no keratin in it. That is why the Canadian Conservation Institute, in its guidance on pests as an agent of deterioration, puts plant and insect fibres in a different category from wool: “Soiling of objects increases their susceptibility to pest attack, in particular silk and cotton fabrics. These fabrics are not usually eaten as food by insects without the presence of added nutritional materials.”

Read that sentence twice, because both halves matter. Clean cotton is a poor meal. Cotton with something on it is a different proposition.

The something on it

The University of California's Pest Notes on clothes moths, written by D. H. Choe and last revised in 2013, is blunt about the conditions: “Fabrics with food, perspiration, or urine stains are more subject to damage.” It also notes that larvae “will feed on synthetics or cotton blends if these fabrics also contain wool,” and that they might use cotton fibres to build their pupal cases even where they aren't eating the cotton itself.

So the risk on a heavy cotton hoodie isn't the cotton. It's what a season of wear left in it. Sweat salts in the cuffs. Body oil along the collar and the inside of the hood. A meal down the front that came out in the wash as far as your eye could tell. Put that garment in a box in June and it stops being inert cloth and becomes a surface with food on it.

This is the argument for washing before storing, and it is a different argument from the one about smell. A hoodie can pass the sniff test and still carry enough residue to interest something. We have written separately about how often a heavy hoodie actually needs washing, and the answer is less often than most people think. Storage is the exception. Before a garment goes into a bag for three months, it gets washed, and it goes in dry.

It might not be moths

Carpet beetles do similar damage and get blamed far less often. Michael F. Potter's ENTFACT-601 for the University of Kentucky College of Agriculture opens on exactly this point: “Carpet beetles are common in dwellings, and their damage is often mistaken for that of clothes moths.” The larvae work the same keratin menu, and the fabric rule is the same one: “Cotton and synthetic fabrics such as polyester and rayon are rarely attacked unless blended with wool, or heavily soiled with food stains or body oils.”

Where they feed is the useful part. Potter describes larvae feeding “within fabric folds (hems, collars, cuffs, etc.) in closets, chests and boxes where items are stored for long periods,” and thriving on “lint, hair, and debris accumulating under baseboards and inside floor vents and ducts.” The population lives in the dust under the baseboard, not in the hoodie. The hoodie is where it goes to eat.

Telling one kind of hole from another

Grazing damage has a look. Potter describes larvae leaving “threadbare spots and irregular holes” as they work along the surface: a thinned patch with a ragged edge, often in a fold. Webbing clothes moth larvae leave patches of silk that pick up excrement and fibre crumbs, and the casemaking species drags a small silk case around with it. Webbing, frass or a case is an identification. One clean hole and nothing else usually isn't.

A single hole with sharp edges, no thinning and no debris is usually mechanical. Heavy cotton takes abrasion at the front hem against a counter edge or a belt buckle, and the yarn eventually gives. Different cause, and no amount of freezing will help.

Storing sweats so nothing feeds

CCI Notes 3/1, written by Thomas J. K. Strang in 1996, sets out a five stage approach: avoid, block, detect, respond, recover. For a wardrobe rather than a museum it collapses into a short list.

1. Wash before storage, and dry fully. Removing the food is the whole strategy. Our washing and care notes cover doing that without wrecking the fabric.
2. Store sealed. Potter's advice is that cleaned items “should then be packed in tight-fitting plastic bags or containers.” A sealed bag keeps a clean garment clean and keeps anything living in the room out of it.
3. Vacuum the storage space, not just the clothes. Potter calls vacuuming floors, carpets and heating vents an effective way to remove larvae along with the hair and lint they live on.
4. Inspect properly when things come out. Strang's instruction is to examine textiles and clothing “front and back; inside and out; in pockets, folds, and sleeves; under collars; along seams.” On a hoodie that means the hood lining, both cuffs, the pouch pocket seam and the inside of the ribbed hem.

September is the right week for it, because the same bin holds the things going away and the things coming out. Our notes on layering a heavy hoodie for a Canadian autumn cover the wearing side.

If you think you already have them

Two treatments come up in the literature, and they disagree with each other, which is worth knowing before you trust either.

Hot laundering is the UC recommendation: “Thoroughly launder them for 20 to 30 minutes in water that is at least 120°F,” which is about 49°C. That will kill eggs and larvae. It will also shrink and dull a heavy cotton garment in a way you can't reverse, so it is a decision, not a default.

Freezing is the conservation route. CCI Notes 3/3, Strang again, in 1997, gives “a practical recommended treatment is -20°C for one week,” with the object sealed in a clear polyethylene bag first so any condensation forms on the outside, and a day at room temperature afterwards before opening. The CCI page on pests goes further for unknown infestations, at -30°C for a week or -20°C for two. The UC Pest Notes suggests a domestic freezer at below 18°F, roughly -8°C, for several days. Those are not the same protocol, and a household freezer often sits at the warmer end. Cold slows insects long before it kills them, so run it longer rather than shorter.

What the evidence doesn't settle

Cedar blocks and lavender sachets are the standard advice and they are mostly folklore, at least as far as the documents above go. CCI Notes 3/1 is built on inspection, sticky and pheromone traps, sanitation and physical control. Scented blocks don't appear in it. That is not proof they do nothing. It is an absence, and an absence is all we can honestly report.

Mothballs are a different thing: a pesticide, not a scent. Health Canada's Residential Indoor Air Quality Guideline for naphthalene, published in 2013, lists pest control products used to kill moths and larvae among the sources of naphthalene found in homes. Use them the way the label says, or not at all.

None of our garments have been tested to the standards or methods named here, and we are not claiming otherwise. What we can say is that heavy cotton is a poor meal, that the residue left in it is the actual attractant, and that a wash before the bin goes in the closet does more than any block of cedar.

Sources

• Canadian Conservation Institute, Agent of Deterioration: Pests, Government of Canada, page modified 2022. canada.ca
• Strang, Thomas J. K., Preventing Infestations: Control Strategies and Detection Methods, CCI Notes 3/1, Canadian Conservation Institute, 1996. canada.ca
• Strang, Thomas J. K., Controlling Insect Pests with Low Temperature, CCI Notes 3/3, Canadian Conservation Institute, 1997. canada.ca
• Choe, D. H., Clothes Moths, Pest Notes Publication 7435, University of California Agriculture and Natural Resources, revised 2013. ipm.ucanr.edu
• Potter, Michael F., Carpet Beetles, ENTFACT-601, University of Kentucky College of Agriculture, Department of Entomology. entomology.uky.edu
• Vilcinskas, A., Schwabe, M., Brinkrolf, K., Plarre, R., Wielsch, N. and Vogel, H., “Larvae of the Clothing Moth Tineola bisselliella Maintain Gut Bacteria that Secrete Enzyme Cocktails to Facilitate the Digestion of Keratin”, Microorganisms, vol. 8, no. 9, article 1415, 2020. pmc.ncbi.nlm.nih.gov
• Health Canada, Residential Indoor Air Quality Guideline: Naphthalene, 2013. canada.ca