Black flies in southern Michigan

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

The lab has received a record number of calls this past week from people in southern Michigan, particularly around the Lansing area, complaining about swarms of small biting flies. Many described the flies as vicious. A veterinarian called to report he had seen at least 15 dogs in his clinic with severe bites on their bellies and around the eyes where the hair is sparse. Fortunately (or unfortunately depending on one’s perspective), I was able to speak to these callers with first hand knowledge because I have been experiencing the same small, biting fly around my house. There was no doubt in my mind that these people were talking about black flies. Black flies are a way of life during the spring and early summer in the northern Lower Peninsula and throughout the Upper Peninsula where there are plenty of clean water cricks, streams and rivers. Black fly larvae develop in these moving waters. Black fly larvae are seen by many as indicators of good water quality so their appearance in southern Michigan just may be a sign that the water quality of our small cricks, streams and rivers is improving. Some of those whom I talked to this past week said they much preferred poor water quality and no black flies.

Black flies are active during the day. They do their best work on calm days with bright sun. Black fly bites typically result in small swollen areas with a bright red center that often bleed a little after the fly has finished its meal. For some people, black fly bites are long lasting and they are terribly itchy. They like to bite around the hair line, around the eyes but any exposed skin is vulnerable. The flies themselves are small, about the size of a fruit fly, and dark colored. They have large wings for their body size and a humped back appearance. Repellents containing DEET may help keep black flies from biting but repellents are not sure thing. The best defense is a head net and loose fitting clothing that leaves no exposed skin or to simply avoid going outdoors when swarms of black flies are present.

Black fly on penny
A black fly that I collected on May 7, 2009 standing
on my driveway south of Mason in southern Ingham
County. I think the genus is Prosimulium.

Black fly close-up
Here’s a close up of the black fly. Notice the humped
back appearance.

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