Thursday, January 26, 2006

The Enemy

I have seen the enemy, and she is Tinea pellionella - the Casemaking Clothes Moth. I've found them in washed fleece (luckily, not anything I was really attached to), old bobbins of alpaca in my closet, in baskets of forgotten stuffed animals, and most commonly, in cobwebs way up in the corners of the ceiling.

They're tiny (about ½"), brown in the adult stage, and flutter about in an erratic manner. Females lay about 40-50 eggs over a period of 2-3 weeks, which are attached to fibers with an adhesive secretion. When she's done laying eggs, she dies. Males outlive females and continue to mate during the remainder of their lives. The eggs hatch within 4-10 days during warm weather.

But it's not the adults that cause the damage - it's the larvae, which feed on protein fibers as they grow inside their little cigar-shaped cocoons, which they later pupate in. Pupation lasts from 8-10 days in summer, 3-4 weeks in winter (unless your home is heated). Generally, the egg-to-egg cycle is between 4 and 6 months, with two generations a year.

So, how do we defeat the enemy? Clean. Moths are attracted to smelly fibers - they like lanolin, sweat, and urine. Wash fleeces and spun yarn before putting them away. Wash or dry-clean sweaters. Get rid of cobwebs. Vacuum.

To kill moths in all stages of life, dry clean, or wash the items in hot water, keeping the temperature above 120°F for 20-30 min. I've seen reports of freezing to kill moths, but you need to get the temperature down to below 18°F for several days. Your kitchen refrigerator doesn't get that cold. You can also fumigate using dry ice.

To prevent infestations, store clean items in an airtight container. For washed fleece, a pillowcase without holes offers good protection. You can also add insect repellents, such as lavender or mothballs. Mothballs are toxic, and typically contain naphthalene or paradichlorobenzene, which leaves an unpleasant odor, and can cause some plastics to soften and melt. As these chemicals evaporate, they produce vapors that, in sufficient concentration, will slowly kill moths and larvae. The only way to assure a sufficient concentration of vapors is to use airtight containers. Cedar contains an oil that can kill small larvae, but it isn't very effective against larger ones.

Traps are available (I've seen them at Rainbow Grocery), but they're really only good for trapping the webbing clothes moth, which is a different species (Tineola bisselliella), that I personally have never seen in my house.

If you want to use an insecticide, make sure that it lists clothes moths on the label. Most insecticides that can be used to kill clothes moths contain pyrethrins, which are also found in most store-bought flea killers, and are derived from chrysanthemums. It kills clothes moths, and can be sprayed directly on fabrics if needed, and doesn't leave a toxic residue. If you have a really bad infestation, call a pest control company.

For more information, see UC Davis' Clothes Moth Information page.