Got moths? There's food somewhere in the house
Q: I live in a 75-year-old brick Colonial. About 10 years ago, I left a bag of unsterilized sunflower birdseed in my basement, and thus began a continuing battle to rid my house of Indian meal moths. After a long fight to get them out of rooms on the main floors, I have isolated them to my basement laundry room, where, I might add, there is no known food source. Since then, I have learned that they will eat just about anything, so I continue to set lures and contact traps. Although I can live with that, I envision them eating something away in the house. How can I get rid of them completely before we decide to sell our house?
A: Indian meal moths, Plodia interpunctella, cannot reproduce for generations without food, be it cereal products, dried fruit, dehydrated vegetables, nuts, candy or dog food. The life cycle, from egg to larva to pupa to next-generation moth, may take as little as 30 days — or as much as 300 days — depending on the temperature and abundance of food. If you continue to trap the moths for longer than that upper limit, there must be a food source.
You've probably long ago learned to store food in the refrigerator or in glass or plastic containers with screw-on lids. But are there old potatoes in a bag? Or a container of dry dog food? Corn gluten meal that you bought to fertilize plants and deter weeds? Be aware that the larvae, which do all the damage, can crawl considerable distances from where the mother moth laid eggs to where they spin a silken cocoon and pupate. So even if you are trapping the moths only in the basement laundry room, the food supply could be elsewhere.
The way you use pheromone lures matters, because by design they are baited to attract moths from some distance. To help rule out the possibility that the traps are attracting moths from other parts of the house, keep the laundry room door closed and place the traps as far as possible from the door. A 15-foot setback from the door is recommended, but your laundry room might be too small to allow that.
If moths still show up in the traps, go through everything in the laundry room and inspect for mats of silky threads, which the larvae spin as they feed and grow. But if the traps wind up empty, any moths still in your house are probably graduates of a food source somewhere else.
The other possibility is that you have a clothes moth problem, even if you initially were dealing with meal moths. The two kinds of moths look similar, but clothes moths are smaller (about half an inch long, compared with the meal moth's 3⁄4-inch length) and are solid yellowish-brown or yellowish-gold. Meal moths have a distinctive reddish-brown color on the back half of their wings.
Jeanne Huber is a writer for The Washington Post.