Q&A: Stoneflies powderpost and black carpet beetles


May 3, 2016

Q: What is the insect in the picture I sent you via email, and what should I do about it? I am finding them on the side of a house in large numbers.
— Dave K., New York

A: It is a stonefly (Plecoptera). These are aquatic insects that breed in streams. The adults emerge in early to late spring. Because temperatures in your area went below freezing when you sent the photo in early January, you probably won’t see any more until later in the spring. No treatment is necessary.

Q: Powderpost beetles are emerging from a customer’s new hardwood floor, which was installed in October. This house has a crawlspace under the area covered by the hardwood floor. Is the manufacturer responsible? Will the beetles infest other areas of the house? Can I prevent that from happening and if so, how?
— John O., Minnesota

A: The answer depends on which powderpost beetle is the culprit. If the frass is very fine (you feel no grit when rubbed between your thumb and forefinger), the beetle is one of the lyctids. If the frass feels gritty, the culprit is an anobiid.

Lyctids only infest hardwoods. Therefore, it is unlikely they will infest anything else in the house. The infestation will die out on its own. The only other option is to tent and fumigate the house, which can be expensive. The exit holes are so small, however, that no one will ever notice them once the frass is gone.

If the culprit is an anobiid, it can infest both hardwoods and softwoods. Most framing in houses today are constructed of pine or fir, both softwoods. However, anobiids require at least 14 percent moisture content to survive. As the hardwood floor dries —it may be below 14 percent moisture already — the infestation will die out on its own. I’d test the framing in the crawlspace: If it’s above 14 percent moisture content, I’d treat it with a borate spray to prevent infestation.

Both powderpost beetle groups require approximately one year to complete a life cycle. Therefore, the hardwood flooring was infested prior to the floor installation. Someone will need to determine the whereabouts of the wood in the preceding year to determine on whose watch the infestation occurred.

Q: Every year, we seem to get a lot of calls about black carpet beetles in the early spring. Then the problem disappears. Sometimes the larvae are noted, but most of the time it’s the adults. Most of these houses do not have wool carpeting, so what is the source? We need some answers so we can address the problem with our customers.
— Luke A., Colorado

A: Black carpet beetles (Attagenus unicolor) are primarily scavengers. Lint containing hair and other animal fibers collect behind baseboards, even in the best-kept houses. This problem is usually associated with homes 5 years old or older.

A black carpet beetle’s typical life cycle is about one year. Emergence of the adults is most common in the spring, which is why you get these calls every year at about the same time. The adults emerge and are out seeking members of the opposite sex. The larvae usually remain hidden on the source, so they are not seen as often.

A good crack-and-crevice treatment along baseboards with a residual insecticide temporarily eliminates the problem, but it is likely to repeat itself next spring.

Email your questions about insect identification and pest management technologies and techniques to Technical Consultant Dr. Mampe at dentomol@aol.com. They will most likely will be printed and answered in one of Pest Management Professional’s upcoming Ask the Expert columns.

Leave A Comment

  1. Jordan says:

    Thanks for sharing this. It’s important that people are able to identify any insects or pests near them and know what they can do.