The discovery of chewed-up yarn is one of the things that can make a knitter's heart sink the lowest. To be sunk further only by chewed-up finished sweaters or weavings.. There is not much to do after an infestation has taken hold, so prevention is your best bet. If you have wool or hairy natural fibers in any form, you should be thinking now about moths before they get you.

Freezing mythology

The most enduring legend about moths is that you can just put the affected wool in the freezer for a few days and kill them. Judith McKenzie actually did a formal study of that, when she was working at a BC museum, and found that it's basically hogwash for the ordinary person. Yes, you could kill some of the moths flying around, but you won't get to the eggs, which are some of the toughest organisms on earth. First of all, you would need some severely freezing temperatures, not your usual medium-soft ice-cream ones. You'd need a Sub-Zero freezer, and you'd need to be able to freeze any food in it beyond what's usually considered reasonable, to a point verified with a reliable low-temperature thermometer. Next, if you only freeze once you're basically selecting for hypothermia-resistant moths. You'd need to wait a while at a controlled suitably warm temperature for hatching, and then freeze again so you can get the larvae that emerge. Even then, you have no guarantee that this will work reliably.

This freezing thing sounds terribly scientific, and that's probably why it's so popular these days, especially as Internet advice :-). It's a shame it won't do you any good. I'm assuming most of you have figured out by now that every bit of folksy herbal advice doesn't work in the least. Cedar chests will make your clothes smell delicious, and lavender sachets as well. But no herb has ever really killed moths in infected wool, even nasty-smelling herbs like wormwood, and none will work as anything more than the mildest of repellents, which truly hungry moths will disregard completely. This holds for all forms of herbs, expensive essential oils being hardly more effective than stale stuff from the supermarket. Don't trust your cashmere to them.

Chemical warfare

The only way that museum people have found to really kill moths and their eggs is to use heavy chemicals. Specifically, the stuff used in Shell 'No-Pest' or 'Vapona' strips, 2,2 dichlorovinyl dimethyl phosphate, is the best Judith's ever found, the only thing that really really works. Do we need to explain how toxic it is? So toxic that even the US goverment has banned it, which should tell you something. However, it's still available in Canada (even though usually they're much more responsible than that!). Should you decide to risk your life and smuggle them, you should know that they work by producing a vapor that's heavier than air. In other words, you should lay them on top of your fiber, in an air-tight container, for at least a couple weeks. Then make sure you thoroughly air the fiber and wash it before attempting to wear it, or work it :-(. And make very sure that no kids or pets get anywhere near the strips at any step of the process. If you dispose of any, talk first to your local toxic waste organization.

In fact, this stuff is so toxic that it really should only be handled by museum conservators, trying to save textiles with historical importance. If you merely find that some of your yarn stash has gotten chewed, just bite the bullet and throw it out. Seriously! Life's too short to try to save even hundreds of dollars of mere yarn, at the cost of your health or that of those around you. Judith likes to remind everyone that sheep are growing ever more fleece as we speak - the supply should be considered basically unlimited.


What you really need to do, when you acquire fiber regularly, is to isolate every bit of new supply till it's proven safe. Whether you get it from the sheep festival, the knitting conference, the local store, or your best friend's garage, there's always a chance that your new stuff might harbour some moth eggs. If you keep it separate, you might cry over the new merino, but you won't be losing your entire stash. Do inspect the new stuff for a good while after you acquire it, at least past the first spring, and don't store larger amounts of fiber together than you'd like to lose. Think of giving the same isolation treatment to fiber in any form, as well as from any source, you're just as much at risk from a vintage sweater as from a new fleece.

Then you're still not safe from any passing moth who'd be delighted to take up residence in any unprotected fiber supply, like one of those lovely open baskets of skeins spinners are so fond of. I like to use Space Bags to store unprocessed (but washed) fleece and yarn. They squish it down to the point where I can cohabit with it in my small appartment :-). They're also thick enough that any infestation won't spread like wildfire, and the lack of air could delay hatching to some extent. Smarter would be to use thick airtight plastic containers that allow you to create a small vacuum. Don't be too cheap here, lack of attention to storage pretty much guarantees that you'll have moth problems sooner or later. The larvae can chew through regular plastic bags, in fact I once found some that had chewed through mylar... imagine my horror! And if you find an infestation, immediately throw out the affected container and all its contents, don't even think about it, don't even peek to see how bad it is if you can help it. Tightly wrap the whole thing in another layer of plastic and make sure it goes out with the trash, don't mess around with donating it to the birds or composting it, much less giving it to schools, OK?

Dirt in general and lanolin in particular are powerful attractants. Just as you should wash your sweaters if you store them for any length of time, you should be washing raw fleece almost as soon as you get it. There are other reasons to dispose of aging lanolin, but not attracting moths is a good one. On the other hand, Judith McKenzie tells stories of keeping some really stinky raw mohair out in an open barrel as a decoy, so the moths would go there first and they could throw it away as soon as they arrived :-). Not a bad idea, just make sure your priceless Peruvian poncho isn't the inadvertant decoy.

If you display textiles in the open in your house, there are some tricks that can also help minimize moth infestations. As all incipient Moms, they like cozy warm dark places, and are adverse to drafts and light. So rather than hanging your textiles right on the wall, make sure there are at least a couple inches for air to circulate freely between the textile and the wall. It's not foolproof, but it's a lot better than nothing.

I also use something which is an alert rather than a preventive: the 'clothes moth alert' by SureFire. It's sort of a roach motel for moths, a cardboard box with a strip of pheromones and sticky sides to trap the moths. It won't do anything but trap flying adults, ie only after they eat your fiber as larvae, and probably after they lay eggs elsewhere. But at least you'll know for sure you have them, and you need to look for infested areas.

For reference, see the very good page from the University of Kentucky Entomology department. It should at least help you recognize whether you have a wool moth infestation, or some other variety.

First published: 5/17/04

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