Carpet beetle
Gary Alpert, Harvard University, Bugwood.org

One day one of our PMPs gave me a call to pick my brain about a particular issue with carpet beetles. He explained that one of our pest customers had an ongoing issue with the pests, and after several months of repeated visits, he was at his wit’s end. I went through the regular diatribe of making sure he searched every nook and cranny for potential food sources near the infestation and he explained that he had gone over the entire house with a fine-tooth comb yet he could not find the source.

I inquired if the customer had pets. “One small dog, but she is very meticulous in cleaning and no accumulated hair anywhere,” was the answer. I asked if there were any small throw rugs made of wool or other animal materials. “There is a small rug in the kitchen where the infestation is seen, but it is made of polyester and has no signs of being fed on by the beetles. We had her wash the rug just in case,” he said.

I was told the infestation was limited to the kitchen area, so I asked about searching cabinets and drawers. “Yes, we went through every cabinet space and pulled everything out but no beetles were found. They are accumulating on the kitchen floor. That’s it. Only adults, no larvae.”

Now I was intrigued since larvae always seem more prevalent and adults are cursory, usually in dead piles along window frames in the room where the larval food source is. I asked, “What about the attic? Could they be coming from there? Perhaps there is a food source in the attic above that area and the adults are migrating after pupation and falling from a ceiling fixture or vent?” He answered, “Well, I thought about that but it is a smooth ceiling with no fixtures or vents above the area and we are not seeing beetles on top of counters or cabinets. Just on the floor.”

Alright, I knew I was going to have to see myself to determine what was going on. We scheduled an appointment and he mailed samples so I could verify they were carpet beetles. Upon receiving samples, I determined they were varied carpet beetles (Anthrenus verbasci).

Left: The old dog food, covered in carpet beetle larvae and caste skins, that was removed from underneath the cabinet. Right: The source of another carpet beetle issue turned out to be old dog food stored in a wall void.

ON SITE. I met the PMP at the customer’s house and he walked me through all of the previous steps and treatments he had already done. The house was, as mentioned, meticulously clean. Next to the kitchen is a small laundry room where the dog’s food and water bowl is located. I am told that the room had been thoroughly scrubbed, including underneath the washer and dryer, even though no beetles were found in that area. “Not even a dust bunny!” I mutter to myself as I peered under the dryer with a flashlight.

We went back into the kitchen and started looking around the area where the beetles were being found on a daily basis. I noticed on the floor near the area is a vent for the HVAC system. I popped off the vent cover and stuck my arm into the duct to feel around. I was able to grasp onto a small amount of debris and pull it out. This consisted of mostly dog hair, an old lollipop and some caste skins from carpet beetle larvae.

“Ah ha!” I exclaimed. “How long has it been since your ducts have been cleaned?” The customer answers, “We don’t have ducks, just the one dog and we bathe her regularly.”

“No, no, no. I mean your air conditioning ducts. Have they ever been cleaned out?” “I don’t think so,” the customer answered.

I explained that there may be an accumulation of hair, lint and other food sources for the carpet beetles inside the duct lines and suggest calling an HVAC company to come check it out. She said it made sense and would call them right away.

I left that day feeling confident that we figured out the problem. About a week later the PMP called back and told me the customer had the HVAC company clean out the entire system but it did not make a difference. She was still finding carpet beetles on the kitchen floor daily. Feeling defeated, we made another appointment to go back out to the house. When I arrived, I happened to notice the foundation vents. I asked the PMP if he had ever gone into the crawlspace. He said it had probably been about a year since doing so. Well, it was the only place we hadn’t looked.

I put on a crawl suit and gloves, grabbed a flashlight and headed out back to the access door. I made my way over to the area underneath the kitchen and immediately noticed lots of dead carpet beetle adults and rodent droppings. I pulled back the insulation material under the area where the beetles were being found on the kitchen floor and was showered with rodent droppings and dead beetles. Looking around the area I noticed many signs of a previous rodent infestation. However, I still didn’t see any carpet beetle larvae. “I don’t think they feed on rodent droppings,” I said to myself. “Perhaps there’s a dead rat in a wall void or cabinet bottom above this area.”

I retreated from the crawlspace, cleaned myself up and went inside to talk with the customer. “It looks like you had a rodent issue at some point?” I asked. “Yep. About five years ago we were seeing an occasional rat but ya’ll took care of it and we haven’t seen any since,” she answered.

I explained that if rodent bait had been used, it is possible that a rat may have died in a wall void or under the cabinets and that could be the source of the carpet beetles. “Oh my God I have a dead rat in here!?” she shrieked. I said I could not be sure but we needed to do some exploratory surgery to see, but it sure seemed like the food source was most likely under the cabinet next to where the beetles were being found.

FINALLY...AN ANSWER. We grabbed some tools and carefully pried off the kick plate for the cabinet and bingo! There it was: Not a dead rat but a giant pile of dog food covered in carpet beetle larvae and caste skins. “Grab the vacuum and a dustpan!” I exclaimed. We used the dustpan to shovel out the dog food and as much of the debris we could get and then used the crevice tool on the vacuum to get the rest. We finally figured out the problem. We were able to find the larval food source (which was new to me because I did not know that carpet beetles would feed on some types of dog food that contain keratin), dispose of it and solve the issue. Since then the customer has not seen any carpet beetles.

This was definitely a learning experience. Since then, there have been many pest issues that we have found stemming from rodents storing dog food underneath cabinet bottoms or in wall voids. Not just with carpet beetles, but also grain beetles, weevils, flour beetles and granary mites. Now, anytime I get a call from a PMP in the field having an issue with stored product pests in the kitchen with no apparent food sources, I tell them to check under the cabinet bottoms and the majority of the time that is where the source is.

The author is technical director at Terminix Service, Columbia, S.C.