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NYSIPM Dairy and Livestock Pest News

Integrated Pest Management in Season Information for Dairy and Livestock Pests

Horse and Deer Flies (Tabanidae) on the Increase!

Horse and Deer Flies (Tabanidae spp.)

This year, there has been a noticeable increase in deer and horse fly populations. These flies inflict painful bites on mammals, including livestock and humans.

Female horse and deer flies possess sharp mouthparts that they use to cut through the skin of their hosts, lapping up the blood that flows from the wound. This biting behavior causes significant distress to livestock, especially when fly populations are high.

THis photo shows the very shape mouth parts on the deer fly. THe mouth parts extend from under the head direct down. They are brownish to black.
Deer Fly Mouth Parts

Photo By: Ward Strong, BC Ministry of Forests, Bugwood.org

THis is a deer fly. It has areas on the wings that are translucent as well as areas that are grayish brown. The body thorax has 3 yellowish and 3 brownish/gray strips running from the head to the rear. The abdomen has sever brown and yellowish strips from perpendicular to the body
Adult Deer Fly

Photo by: Sturgis McKeever, Georgia Southern University, Bugwood.org

Horse and deer flies are commonly found near tree lines and wet areas, as they thrive in aquatic and semi-aquatic habitats during their egg and larval stages. Most species prefer environments such as streams, ponds, or swamps, though some are found in wooded areas with abundant leaf litter. The development time from egg to adult varies widely among species, ranging from 90 days to several years.

Life Cycle

Horse and deer flies lay between 100 and 800 eggs on vegetation above wet areas. Upon hatching, the larvae drop into the water or moist ground below. Depending on the species, the larval stage includes 6 to 13 instars before pupation. These insects typically overwinter in the pupal stage.

Control Measures

Managing horse and deer fly populations on cattle is challenging due to the flies’ quick feeding habits. They land, cut open a spot, and take a blood meal rapidly, reducing their exposure to control measures. These flies often concentrate in specific areas on a farm.

For farms experiencing significant fly populations, various traps can be used to manage their numbers, including the Horse Pal, H-Trap, and Epps Trap. These traps have been found to be effective in certain situations. Placing traps in areas where flies are most prevalent can help reduce their numbers locally. It is essential to position the traps out in the open but away from cattle, as the animals may damage them.

The Horse Pal is a unique and effective fly trap that stands about 6 feet tall. It features four legs draped with cloth, with netting wrapped around them, leaving the bottom portion open. The legs taper inward towards the middle, where a jar is positioned. The netting also covers this tapered section. Hanging from the center of the trap is a large black plastic ball that almost touches the ground, which attracts the flies. When flies land on the ball, they realize it's not an animal and instinctively fly upwards towards the light passing through the netting. As they ascend, they become trapped in the jar at the top, which functions like a fish trap.
Horse Pal Trap
The H-Tra is an innovative and highly effective fly trap that stands approximately 6 feet tall. It features a metal post that supports a plastic cone with a diameter of about 1 meter. This cone tapers towards the top, where it connects to a jar. The bottom of the cone is suspended roughly 3.5 meters above the ground. Inside the cone hangs a large black ball positioned about 1 meter from the ground, designed to attract flies. When flies land on the ball, they quickly realize it is not an animal and instinctively fly upwards toward the light filtering through the cone. As they ascend, they become ensnared in the jar at the top, which operates similarly to a fish trap.
H-Trap
This is a large black trap designed to catch horse or deer flies. It consists of four large black plastic sheets mounted on posts, forming a wall about 5 feet wide and 6 feet tall. In the middle of the trap is a 3.5 by 10-inch opening. Below this opening is a large plastic dish, about 3 feet long and 2 inches deep, designed to hold soapy water. The dish is mounted on the two outer posts. Above the dish is a clear plastic V-shaped fly deflector. Flies, mistaking the trap for an animal, will attempt to fly through the opening and are then deflected into the soapy water below, effectively trapping them.
EPPS Trap

By strategically placing traps and managing habitats, farmers can alleviate some of the issues caused by horse and deer flies, improving the well-being of their livestock and reducing the nuisance to humans.