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Pesky Deer Flies

University of Minnesota Extension, Stearns County News
June 21, 2017        
Source:  Beth Berlin, Extension Educator-Horticulture
University of Minnesota Extension
Stearns, Benton, & Morrison Counties

Pesky Deer Flies
By Beth Berlin, University of Minnesota Extension

ST. CLOUD, Minn. (06/21/17) — Minnesota summers always seem too short and as wonderful as they are outdoor pests like the deer fly seem to put on damper on many people’s experience. These fast flying, blood sucking flies are beyond an annoyance and bites can be quite painful.  Deer fly season in Minnesota is typically from mid to late June and runs through early August, but flies have been known to persist longer. When the season is in full swing, enjoying outdoor activities or doing yard and garden chores becomes significantly less enjoyable.
Deer flies have two blade-like mouthparts that cut the skin and cause flow of blood out of the wound. Females are the flies that will then use their sponge-like mouthparts to lap up blood; males are similar but are not capable of biting and feeding on blood. Deer flies are 1/4 - 3/8 inch in length with a yellow or black colored body. Their wings have dark bands or patches on a clear background and they have iridescent eyes.
Deer fly larvae live in aquatic or semi-aquatic areas like marshes, ponds, or streams. Adults will be found in these areas, but they are strong fliers and will be found several miles from breeding grounds especially along woodlands.  The flies are known to linger in more shaded, wooded areas and attack their prey upon sight of first movement. Activity is highest on sunny, calm days.
As indicated, deer flies are strong, fast fliers and will target the head, neck, or shoulders of humans. These pests will also attack deer, horses, cattle, and dogs. To date, deer flies have not been known to vector disease in Minnesota to humans. However some people have suffered allergic reactions to these bites.
Control of these pests is nearly impossible.  Personal protection such as wearing long sleeves, long pants and hats can help minimize the number of bites.  Protection from mosquito repellents containing DEET and permethrin is inconsistent. If used, be sure to read and follow the label. Some methods to help reduce the population in a given area include placing a sticky substance on cards, cups, buckets or other objects and affixing to lawn mowers, vehicles, or even hats.  The sticky, non-toxic substance is sold under several trade names at your local garden centers, it is also used on trees to prevent pests such as the forest tent caterpillar from crawling up the trunk.  Research done at North Florida Research and Education Center, University of Florida has indicated the deer flies are attracted to bright blue moving objects, and will in turn get stuck in the sticky substance on these objects. As ridiculous as this sounds and looks, those who deal with deer flies often are willing to try anything. One last tip is to use a hand cleaning material that contains citrus extract to help remove the sticky substance from your hands.
To prevent deer flies from forcing you indoors this summer, try different measures to prevent them from biting you and still enjoy the gardening and the outdoors.

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