QUESTION:

Is there a pesticide that works against deer flies? The cabin, which is 70 or more yards from the lake, is where I need control. Thanks.

ANSWER:

If it helps at all I can empathize with you. My wife is from Wisconsin, and while I dearly love the state and the beautiful hardwood forests in the northern half, I dearly hate the deer flies. Frankly, I don't know how people can stand it outdoors during deer fly season without carrying the mandatory net that I do to catch and kill these nasty blood feeders. I swear I've killed over a thousand on any 1-week vacation back there, and one time caught over 20 in the net at one time when I walked out of the woods and they spotted me and decided I looked like I taste good. Only females feed on blood, and one of their main stimuli is motion, attracting their attention to a potential blood host.

The consensus of opinions from University resources continues to be that insecticide control of deer flies and horse flies is not a good option. You may be able to spray small areas around a home, such as foliage of trees and shrubs, and with a residual insecticide may kill some of the resting adult flies as they perch on this foliage. But, given the extended season when these flies are active and the wide areas of woods they occupy, these kinds of applications would have to be too extensive and too frequent to make good economical (and environmental) sense. The larvae develop in just about any wet situation, including in the mud at the bottom of ponds, lakes, and streams, but also in wet soils and wet buildup of organic materials, such as the thick layers of leaves on the ground in your forests. This makes it virtually impossible to control The Source of the problem, which is essential for effective fly management. If you cannot control the source then you are stuck with dealing with the adult flies.

Since pesticides are of little value what else is left? Well, repellents may have some effect, although my experience is that deer flies are not nearly as respectful of DEET repellents as are mosquitoes. But since deer flies attack primarily around the head and neck and upper arms the repellents could be applied there and reapplied frequently to keep them in place, and this will at least help. A person active outdoors can wear a net over the head, dropped down from a wide-brimmed hat to keep it off the skin, and this is very effective, along with long sleeves and long pants. There are some interesting deer fly traps that are patches that can be worn on the back of the hat, and these seem to attract the deer fly which then is stuck on the trap. There also are area traps of shiny sticky surfaces that seem to fool the flies into flying into them and getting stuck, and these will reduce the overall numbers of the flies.

What I am suggesting here is that YOUR role in deer fly management if probably more advisory than anything else. Using insecticides is going to be disappointing and probably result in an over-use of materials with little to show for it. Controlling the larvae is out of the question. It gets down to options that the customer needs to do for himself, with physical barriers, repellents, and traps to capture as many flies as possible.

View past Ask Mr. Pest Control questions.