Clothes Moths

The shame of wool moths. Nobody likes to talk about it, but let's face it: many bikers, especially randonneurs, own their share of wool, and that wool is not always stored clean. These conditions favor wool moths. What I've learned might be useful to others, and if anyone has more knowledge to share I'd like to learn more.

We had a wool moth infestation. It probably traveled up with me from Portland, lay dormant for years, and resurfaced in 2004 or so. I thought we cleaned the problem up, but I have now learned the measures I took were probably entirely ineffective. The moths came back last summer. (Or, it may have been an infection from a wool item bought used. Now I quarantine wool that comes into our house, regardless of whether it was bought new or used.) I threw out some expensive suits and one very nice wool hiking sweater. I took measures. The problem abated, but has not entirely gone away.

When the problem recurred last winter, I found moth damage on the sweater and two wool suits. I threw out the now hopelessly damaged items and started researching.

There are two problem moth species: the webbing moths and the casemaking moths. The casemaking moths are rare here, and the casings they leave behind are obvious. You can get pheromone traps for the webbing moths. The "Pro-Pest" ones seem to work well and are available via Amazon and etc. The traps attract male moths, which then get stuck to the trap. They are supposed to be good for 3 months, but seem to still be pretty effective after 6 months, at least at room temperature.

When I discovered the moths, I ordered some traps, and looked into what wool moths liked and what killed them. Clothes moths like dark, warm places that smell like humans. They lay their eggs in wool that has human sweat, urine, or the like on it, as this is what the larvae eat. Apparently they don't need the wool to live so much as our blood, sweat, and tears, so to speak. So clean wool is usually safe. Besides wool, moths will sometimes infect silk, down, and in rare cases even cotton.

Dry cleaning kills the moths, so everything dirty that was dry-clean only went straight to the cleaners. (Washing and drying clothes does not reliably kill moth eggs.)

Cold kills moths, but slowly. Suddenly taking clothes from room temperature to a cold freezer and leaving them there for a week should do it, but I am not super confident in this method.

Heat kills moths. Half an hour at 120 degrees should do it, so I cranked the sauna up to 140 degrees and put the remaining clothes in for about an hour. This method is more difficult than it seems. I used a radiant thermometer to find out what temperature the clothes were really at. Just because the room is 140 degrees doesn't mean the clothes are.

Permethrin kills moths. We have plenty of permethrin around. It's an insecticide. We treat clothing we are going to wear in areas where malaria is endemic. Once it dries on the clothing, it's almost entirely non-toxic to people. Also, permethrin repels bed bugs. We've never had bed bugs, but we visit a variety of hotels, so I treated our luggage inside and out with permethrin to discourage bed bugs from hitching a ride on our luggage. And, permethrin kills clothes moths. So I put on a respirator and the big rubber gloves and sprayed down all of the seams and crevices of all the closets that had had wool in them.

The permethrin and sauna treatments were hot, sweaty jobs, but seemed to work. I put the moth traps in the closets, and, well, moved on.

But I did some more research. I found out two interesting things:
- Moth speed of development is highly temperature dependent. This means that they are more likely to emerge in the summer.
- Carbon dioxide kills all life stages of moths.

A CO₂ concentration of as little as 15% should kill moths eventually, and higher concentrations should kill them in a few days. I decided that, to be sure, I'd shoot for a CO₂ concentration of over 95% and hold it for a week.

My first test was with a more-or-less airtight plastic storage box that I put the skiing woolens in at the end of ski season. I put about half a pound of dry ice wrapped in a rag at the bottom, put a heavy book on the lid, and left the latches open. As the dry ice sublimated ("melted"), the CO₂ gas would collect at the bottom, and displace air at the top. At the time, I didn't have a real way of measuring if it worked, but recently I found out it had. It doesn't take long doing this to realize that you can smell really high concentrations of CO₂. It's the smell of getting a fizzy drink up your nose, without the wet part. So, when I opened the box of winter woolens recently, I could smell the CO₂ that had been there since spring. I have to think that any moths or moth eggs were long dead.

I had decided to treat our woolens once or twice a year, just to be safe. My method was to buy Space Bag storage bags. These bags seal air tight, and they have a vacuum port. (Several of these bags are shown in the picture, above.) Put the woolens in the bag with a chunk of dry ice wrapped in a rag. Suck all the air out. Close the cover on the port until the bag starts to inflate. Open the port. As the pressure inside the bag rises, it will push air and CO₂ out the port, until the final CO₂ concentration will be quite high. Leave for a week. It works great. I know, because after I open the bags after a week, I can smell the CO₂ in the bag quite easily.

But a funny thing happened, just as I was about to embark on the Space Bag project: I had been checking the moth traps every week. Never a moth. I decided to Space Bag treat the woolens at the end of an unusually warm and dry August.

Literally as I was collecting the woolens to bag them, I checked the traps one last time. They all had moths, in some cases, quite a few. So now I know the traps work.

Where did the moths come from? I don't know. I literally checked all the wool and silk in the house, including carpets. Nothing. No holes, no dead moths, no webbing, nothing. Did they come from outside the house? Maybe. They might also have come from some bulky wool sweaters where damage might not be obvious.

Actually, none of my theories for where the moths came from are all that persuasive. So I don't really know. I treated with CO₂. Most of the woolens are in airtight storage now, and almost all of the rest will be soon. I ordered fresh traps. I plan on treating the woolens twice a year until we go two years with no moths in the traps.

To be continued....