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When will the yellow fly and deer fly season will be over in New Hanover County?

Ken Little
Deer fly and horse fly

Drawings of a deer fly, left, and horse fly, right. (Courtesy of the University of Kentucky College of Agriculture)

Al Hight, New Hanover County cooperative extension director, is sympathetic to those plagued by the pesky insects this time of year.

But Hight has few remedies to suggest.

“The real saving grace is that the life cycle should be complete soon and the problem will take care of itself,” he said in late July 2011.

Hight forwarded an Ohio State University Extension fact sheet that offers some disquieting information.

“Female horse and deer flies are vicious, painful biters. They feed on the blood of cattle, horses, mules, hogs, dogs, deer, other warm-blooded animals, and even humans. These flies cut through the skin with their knife-like mouthparts and suck the blood for several minutes. When they fly away, a drop or two of blood usually exudes from the wound, permitting secondary feeding sites for other nuisance insects,” the fact sheet states.

“Biting deer flies frequently attack humans along summer beaches, near streams, and at the edges of moist, wooded areas. Some people, when bitten, suffer severe lesions, high fever, and even general disability,” it continues.

Symptoms include allergic reactions to hemorrhagic saliva poured into the wound to prevent clotting while the fly is feeding. A person can become increasingly sensitive to repeated bites.

Nuisance Autumn horse flies “buzz” people and rest on porches during late summer, according to the fact sheet.

Deer flies are slightly larger than house flies, and mostly yellow or black with darker stripes on the abdomen and dark markings or patterns on the wings. They have brilliant green or golden eyes with zigzag stripes. Deer flies frequently attack humans, whereas horse flies usually attack livestock, the fact sheet said.

Adults of most species are seen for only about one month, but often there is an overlapping succession of species during the season.

“No satisfactory methods have been developed for control of horse and deer flies. It is impractical in most regions to eliminate the breeding areas. Draining marshes and wet meadows where flies develop is of the greatest value, but should be done in such a way as to preserve the desirable wildlife of such areas, if possible” the fact sheet said.

There is some good news.

“Fortunately, the season for deer flies is rather short, usually four to five weeks in June or July, and three to four weeks in August for horse flies. If the problem lasts six to eight weeks, there may be several species present or that species lasts longer than most. Humans are better able to protect themselves than wild or domestic animals by swatting flies away and by using repellents,” according to the fact sheet.

The greatest deer and horse fly activity occurs on warm, sunny days when there is little or no wind. A slight drop in temperature or a sudden breeze reduces biting attacks. Deer flies seem to be attracted to moving objects and dark shapes. They attack humans especially around the face and neck areas, and four to five deer flies can attack at one time, according to the fact sheet.

Added Wes Watson, a professor of entomology at N.C. State:

“In our studies on horse farms in Central North Carolina, we find there are overlapping generations of horse and deer flies during the summer months. There may occur at one time several species that will be active for a month or so. These will often be replaced by another species. Typically, the number of flies taper off in August then become relatively rare in September.”

Watson said that some studies done in the 1970s included the may fly.

“The may fly is most active in May and June. Activity began to decrease in July but some flies were active at relatively low levels to the end of the season,” Watson said.

“I guess the short answer is to expect the fly numbers to decline over the next few weeks. Although fly numbers are expected to drop, there will be some activity throughout the summer,” he said.

User-contributed question by:
Ms. Morrison

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