Tiny black bugs in window sill in North Dakota winter

Asked December 13, 2020, 1:37 PM EST

About a month or so ago, I've noticed the black bugs in the living room window sil. I haven't really noticed them in other windows around the apartment but this one. There are a few house plants in the area but since the first time I noticed them we haven't watered them, so it's been over a month. I also haven't seen any movement by the plants. Around September or so we did have a few fruit flies in the kitchen, but I was able to get ride of those, so don't know if that is prevalent. When I first saw them I sprayed some Raid for a few days at the area and it seemed to have solved the problem, so I stopped. Today though, I noticed a lot of them again. Everyonce in a while I'll see one flying around the house, but they all seemed to be contained in this window sill.

Cass County North Dakota

1 Response


I can't tell for certain what these are, but based on the photos and your description, they are either dark-winged fungus gnats or moth flies (a.k.a. drain flies). And both could be present. Management for the two species is different. Dark-winged fungus gnats are nuisance pests of indoor plants, and their larvae thrive in wet potting soil. Adults are short-lived, and control is aimed at the larvae. Re-potting into fresh soil is recommended, and don't overwater. If re-potting isn't possible, use a potting soil insecticide labeled for use on indoor houseplants that contains the active ingredient imidacloprid. This will control the larvae. There are a few products, such as Bonide Systemic Housplant Granules that should be available at local hardware stores. Be sure to read, understand and follow the product label.

Drain flies (moth flies) are commonly found in sewage pipes and sink drains. The larvae live in the organic material that accumulates on the sides of the pipes, especially in sink drain traps. In this case, thorough cleaning of drains and pipes is recommended. In order to determine which drain(s) has them, tape a clear plastic container over the drain, leave it for at least 8 hours, and see if any adults accumulate in the container. Suspect drains should be cleaned with a flexible wire brush. If possible, remove the drain trap and thoroughly clean it and the adjacent pipes that the trap attaches to. Drain cleaning products that contain special enzymes that break down and remove organic accumulations are available, but I don't know how effective they are. Insecticides will kill adults, but not larvae. The source of the problem must be eliminated.

Since you're here in Cass County, I suggest you collect a sample in a ziplock baggie and mail it to me. That way I'll be able to tell you what you have. My mailing address is: Patrick Beauzay, NDSU Plant Pathology, Dept. 7660, P.O. Box 6050, Fargo, ND 58108