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Horse fly can be any member of the insect family Tabanidae (order Diptera), but specifically members of the genus Tabanus, which are biting flies, a legendary nuisance to livestock, pets, and humans.

Since May this year, we are experiencing high horse fly infestations across regions, because of the frequent rain and humidity in Alabama. I have called for horse images and specimens for identification and to enable recommendations for control.  A sincere Thank You to all (extension agents and clients) who responded in actions.

Review of all the images and specimens indicate we are dealing with one species: Tabanus trimaculatus. This identification has been confirmed by the livestock fly expert, Dr. Dan Kline, at USDA/ARS.

Horse flies are woodland dweller, enjoy moist areas and habitats. They deposit egg masses on vegetation in or near water where the larvae can burrow into moist soil. The larvae are cannibolists, eat organic matter and small arthropods and replies.

Horse fly picture taken by Patty Tyler (right).

Males don't bite, but live on plant nectar and pollen.These large, stout-bodied female flies are powerful and agile flies, circling or chasing their targets with deadening persistence to deliver painful jabs to the skin and to suck blood. The flies only stay in contact with a host for a few minutes to get the blood-meal and then they are gone until they need to eat again which is every 3-4 days. Beyond blood-feeding, horse flies, on rare occasions, carry diseases pathogens to livestock and horses.

Often, horse flies are far too mobile and numerous to control with insecticides: topical pesticides is ineffective due to horse fly behavior, but short term control is possible.  Aerial applications and treating for the larvae are ineffective. Repellents don't work well either. Thus it is not an easy job to achieve horse fly control. So what is an Alabama to do?

Cultural controls

Reducing the amount of standing water on your property will help keep horse fly populations low, though this is easy said than done. If the fly problem is in stall, get manure out of the stall quickly, deposit far away from the barn, and clean all wet areas. The manure needs to be dragged to distribute in a THIN layer over a wide area, so to let it dry out quickly. Fly      larva cannot develop in dry environment.

Avoidance of tabanids is often the best strategy. Don't confine pets to tabanid-infested areas, and move them indoors if possible.

For humans, horse flies can be gratifyingly inept. They are not very sneaky, having extremely noisy flight, and they can be slow to bite after landing on the skin. Horse flies are therefore vulnerable to a well-targeted slap or swap.

But this may not be an easy job to protecting animals from being attached. The best option is to provide shelter for the animals or pasturing them away from infested areas. Another option is feeding animals with a supplement containing IGR. It is better start this in later Match until fall.

Traps have been proven to be practically well in providing effective control. 

If the issue is in residential area: Using traps to reduce fly population. Traps can be box traps, sticky traps, and light traps. Female flies are attracted to carbon dioxide, light, and moving dark objects).

Traps specifically designed for capturing horse flies are H-traps, box traps, and Nzi traps. Mosquito Magnet Independence CO2 baited trap also work well in capturing horse flies, but it is expensive.  None claim to conquer them all but you can kill many. These commercial traps utilize horse fly behaviors to lure flies with CO2, dry ice, or dangling black ball coated with Tanglefoot.

Tabanid traps can be bought or home-built using the same general idea. You can hang black balls/spheres where the flies frequented, trap flies in an inverted galss jar or coat the black balls with Tanglefoot (a sticky petroleum product available at hardware stores).  Since tabanids are attracted by carbon dioxide, it might be interesting to try adding dry ice to your trap design.

Fortunately for us, tabanid numbers tend to outburst suddenly, and then go away within a short period of time.

Home-made ball coated with Tangelfoot. Photo from Dr. Dan Kline, USDA/ARS.

Xing Ping Hu

Department of Entomology and Plant Pathology


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