A recent survey of North Carolina horse owners conducted by Dr. Wes Watson, Department of Entomology, North Carolina State University, indicated that horse flies and deer flies (family Tabanidae) were at the top of the list for most horse owners as their most troublesome pest. These flies were listed as common seasonal pests by 89 and 81 percent of the respondents, respectively.
Because insecticides and repellents provide only marginal horse and deer fly control, trapping is an approach that may be worth considering. Dr. Watson began a study of two commercially available tabanid traps last summer and the results are encouraging. It's a little too soon to claim victory, but the traps show potential for reducing horse and deer fly populations in localized areas such as around horse pastures and exercise paddocks, golf courses, swimming pools and yards.
Trap Designs
The Horse Pal is a commercial version of a basic box and canopy design called the Manitoba trap that has been used in research for years. These pyramid-shaped traps take advantage of the tabanid's attraction to movement and dark colored objects. The trap uses a dark decoy (black sphere) suspended below an open box or canopy structure. Flies are attracted to the trap's contrasting colors and movement of the suspended sphere. They enter the trap's open bottom and fly upward to be captured in a large jar at the top of the trap.
A second type of trap was designed and developed in Oklahoma and is a relatively new kind of trap. Called the Epps trap, it is markedly different in appearance from the Horse Pal. It consists of four pieces of black sheeting and two water-filled troughs above which narrow plastic windows are positioned. Two pieces of sheeting make up the large central panel of the trap where both trough-window sections are located. One trough-window arrangement is positioned high on the central panel and one low on the panel. Two narrow side panels extend from the central section at 45 degree angles, giving the trap a zig-zag appearance when viewed from the top. The size and shape of the trap apparently attracts horse and deer flies who mistake it for a large animal. The flies crash into the trap and fall into the water filled troughs where they drown. A commercial version of the Epps trap became widely available in 2000.
The Field Study
Pairs of traps were placed on two farms in central North Carolina. Traps of each pair were separated by a distance of approximately 75 meters. Traps were located around pastures between larval habitats and resting sites used by adult flies. Catches were collected twice a week during peak tabanid season, diminishing to once a week later in the sampling period. The data reported here is from the two study farms where tabanid activity was sufficient to provide good information about typical horse and deer fly pressure. Weekly trap catches were counted and identified to species through the 12-week sampling period from June 19 to September 6, 2000.
The total number of flies trapped during the period was not markedly different for either trap. The two Epps traps collected a total of 1,473 flies, compared to 1,442 flies for the two Horse Pals. Eighteen species of horse fly and 6 species of deer fly were trapped, with little difference in the species profile for either trap design. The distribution of capture for each type of trap did vary considerably over time however. The Epps trap caught significantly more flies between June and mid July, but failed to sustain its advantage into the later part of the trapping period. There was no real difference between the trap catches through the end of July. By August, tabanid populations began to drop off considerably and remained low until the end of the trial. The Horse Pal trapped significantly more flies than the Epps trap during this latter period. Overall, the Horse Pal performed more consistently throughout the fly season even though its average catches during the peak period in July were considerably lower than the Epps trap.
Total horse fly catches in excess of 700 for each Horse Pal and Epps trap in the study was encouraging. Unfortunately, the number of deer flies was relatively low for both traps during the same period. The low number of deer flies suggests that the Horse Pal and Epps trap are not effective for this group of tabanids. To be fair, however, their performance may not have been accurately determined in this study. The traps were placed after the deer fly season (generally, April through early June) had abated in those areas. It is also possible that the resident deer fly populations were typically low at both sites.
Assembly and placement of each type of trap presents its own advantages and disadvantages. Both were easy to assemble, with a slight advantage going to the Epps trap. The lighter and smaller Horse Pal was easier to move from place to place once assembled. The simple anchoring device supplied with the trap also made it easy to secure the Horse Pal in place. The Epps trap on the other hand required the use of four metal fence posts (purchased separately) to support and anchor the trap. The posts insure that the trap is well secured, but make it more difficult to move the trap from one location to another. Weekly removal of dead flies is acceptable for both trap designs. Flies trapped in the jar atop the Horse Pal died within 24 hours and the week's catch was easy to remove. Flies trapped in the water-filled troughs of the Epps trap were removed twice a week during the study for identification. Otherwise they can be dipped out with an aquarium net or sieve once a week. Finally, we found it was sometimes necessary to replenish the soapy water in the Epps traps every few days during particularly hot, dry weather.
In addition to continuing the trap comparisons for one more summer, a study site will be established to measure the long term effectiveness of these traps in reducing localized horse and deer fly populations. Stay tuned.
Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age or disability. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.
Last modified on May 28, 2001 by Stephen J. Toth, Jr.
