QUESTION:
I have a customer who is having problems with Horseflies around her pool. She lives in a rural area with no livestock within a mile or so. The pool is painted white with a slide that is also white. The flies seem to be attracted to the slide area. The pool water is treated traditionally with chlorine. The cutomer does not want to use any type of sticky traps. Any suggestions?
ANSWER:
This is going to take some diplomacy and education of the customer to help her understand the severe limitations YOU have in dealing with horse flies and deer flies (Family Tabanidae). These nasty blood feeding flies have no respect for insect repellent and are often not even courteous enough to anesthetize the bite area the way mosquitoes do, so their bites can be very painful. Some of the biggest horseflies get over an inch long with correspondingly large mouthparts, and their method of feeding is to use the scissors-like blades of their mouth to slash open the skin, which then is lapped up by the spongy parts. Only female horse and deer flies feed on blood.
Perfect fly management involves controlling the source, meaning the place where these adult flies originate from. This is fine for house flies or vinegar flies where some unsanitary condition is available, but horse and deer fly larvae live and develop in just about any moist situation, feeding as predators on other insects in that habitat. Deer flies may develop only in aquatic habitats like ponds or lakes and horse fly larvae live in moist soils, damp, rotting wood, and other wet or aquatic habitats. Their large larvae are even known to feed on tadpoles and other small vertebrates. Because of this varied living arrangement it makes it difficult to impossible to control the larvae of these flies. In the dense forests of the Upper Midwest, for example, where it rains throughout the summer, just about anywhere within the forest floors the larvae could be found.
So, this gets you down to having to confront the adult flies, and this can be frustrating. Your customer likely wants NO more horseflies pestering her family, and this is an unrealistic goal that she needs to understand and accept. You may be able to reduce the problem, but not eliminate it. The flies that are hanging around this area of activity are probably female flies that are attracted to the people and the potential for blood meals. The pool itself probably has nothing to do with it, so the color and the chlorine will not be factors. The flies may be drawn to shiny surfaces, so this may be a reason they seem to hang around the slide. Otherwise, the females seeking blood are drawn to movement and carbon dioxide, and they will sense the presence of people around that area.
Insecticide applications are of little value. Fogging the air to kill them will not result in any particular kill and would have to be done repeatedly. Residual insecticides applied to surfaces are also unlikely to intercept the flies. These are extremely strong fliers that may come from long distances to seek food.
Despite her reluctance to use sticky traps, this may be the best or only option, and deer fly and horse fly traps are available. These often use the color blue to attract the flies to the glue surface and they then are stuck the moment they touch it. I would look around on the internet under “horse fly traps” to see what is available and what may be acceptable for this customer. The options are really limited.
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