Deer and horse flies are from the Tabanidae family for which there are 35 different species in Florida. Both are a pest to cattle, horses, and humans. While they are from the same family, deer flies are in the genus of Chrysops and horse flies are from the genus Tabanus.

The yellow fly, on the other hand, is from the Diachiorus ferrugatus, also known as Fabricius. It is the fierce biter in Florida. As with many biting insects, it is the female who is responsible for biting. The males prefer pollen and nectar. They are active during daylight hours and are the most active in the hot summer and early fall.

Horse and deer flies can be found worldwide, they have not been seen in Hawaii, Greenland, or Iceland. Florida produces the largest population due to the availability of suitable habitat. Its mild climate, permanently wet and undeveloped areas are good breeding areas.

All three breeds prefer aquatic vegetation to lay their eggs, you will also find them on overhanging foliage, projecting rocks, and sticks. The mass of their egg’s ranges from 100 to 1000 eggs. You will find the adult tabanids in Florida between May and September. Although they have found egg masses as late as October 13th.  Their lifespan is 30 to 60 days.

They wait in shady areas under bushes and trees for a host. Mostly, they use sight as their main host-finding mechanism, carbon dioxide does play a role also. Most prone to an attack are dark colored moving objects. Attacking during the daylight hours, their peak time is between sunrise lasting roughly three hours. Two hours before sunset they have a second peak. On cool overcast days, the attacks are low.

Yellow Fly - Tropic Moon Media

Biting on livestock occurs on the abdomen, legs, and neck with deep wounds that cause a flow of blood. With scissor-like action, the mandibles and maxillae penetrate the skin and pump anticoagulants through their saliva are into the wound. The blood is then ingested through sponging labella. When the flies are disturbed while feeding on one animal and then begin feeding another, it is possible that pathogens are transmitted at the same time.  It is known deer files transmit Tularemia and horse files transmit Anthrax. In livestock, fly attack cause lowered gains and low milk production. There can be 100 flies feeding on an animal at one time. Feeding for six hours twenty to thirty flies are capable of taking 100 ccs of blood.

Currently, there are no adequate means for managing the populations. Although traps have been effective in areas such as yards, camping sites, and swimming pools. On the Atlantic Coast, traps have reduced their numbers, as well there have been reductions around cattle that are confined to manageable areas. It has been suggested on a large-scale to manipulate their habit. This can be done by removing unnecessary woody plants from residential areas or draining wet areas reducing their breeding habitat.

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