How to avoid deer fly bites, according to science

An experiment with a sticky fly trap in a Canadian forest suggests you will get more deer fly bites if you walk around than if you sit still.

If you are being pestered by deer flies in the woods of North America this summer, don’t run away – try sitting quietly instead. An experiment shows that people attract more of the biting insects while walking than while sitting still.

A sticky fly trap worn on a hat catches many more deer flies if you walk around
April DeJong

Deer flies (genus Chrysops) are a major pest for both wild and domestic animals, with the distress caused by their painful bites leading to weight loss and reduced milk production.

Woodland caribou spend more time lying down in June and July, when deer flies are most active, so April DeJong at Trent University in Canada decided to see if that might be a way of avoiding bites.

For several weeks, DeJong spent her lunch break as fly bait, either walking along a forest trail or sitting quietly beside it for 20 minutes at a time, wearing a hat with a sticky fly trap on the back.

Deer flies are commonly encountered in forests in the summer in the US and Canada
Paul Reeves Photography/Shutterstock​

The trap caught five times as many deer flies when walking versus sitting and the number of flies caught per minute also declined much faster when sitting. “Sitting was much nicer than walking,” she says. “When I was walking, they were always surrounding me and it was difficult not to swat them.”

DeJong says the difference is probably because moving continually exposes the host to new flies, while sitting still only attracts the ones already nearby, which are then either trapped on the sticky paper or sated with a blood meal.

The sitting-still technique might not be useful against all biting insects, warns Bridgett Benedict at Texas A&M University. Mosquitoes, for example, can use smell to find hosts from far away and their sheer abundance means sitting still would just leave you a sitting duck. “There are a lot of different insect groups that are attracted to mammals for different reasons, so I would be careful to apply what they found too broadly,” she says.

Journal reference:

Canadian Journal of ZoologyDOI: 10.1139/cjz-2023-0010

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