Description
The family Tabanidae, commonly known as horse flies, and deer flies, contains pests of cattle, horses and humans. In Florida there are 35 species of Tabanidae that are classed as economically important. Horse flies are in the genus Tabanus, deer flies are in the genus Chrysops. The yellow fly, Diachlorus ferrugatus (Fabricius), is known as a fierce biter in Florida. Like mosquitoes, it is the female fly that is responsible for inflicting a bite. The males are mainly pollen and nectar feeders. Tabanids are most likely encountered in hot summer and early fall weather. They are active during daylight hours.
Horse flies and deer flies are world-wide in distribution. They are, however, unreported in Hawaii, Greenland, and Iceland. In the United States, Florida produces a large population of tabanids because of the availability of suitable habitat. Florida's mild climate and large permanently wet and undeveloped areas provide good breeding areas.
Adult tabanids are encountered in Florida between the months of May and September. Most species overwinter in the larval stage and pupate during the spring and early summer. An egg mass has been found as early as May 5th and as late October 13th. Most have a year-long life cycle but some larger species may take two or three years. Adult life span is 30 to 60 days.
Tabanids lie in wait in shady areas under bushes and trees for a host to happen by. Sight is the main host finding mechanism, but carbon dioxide and odor also play a role. Moving objects, especially if dark colored, are most prone to attack. Attacks occur during daylight hours with a peak beginning at sunrise and lasting three hours. A second peak is two hours before sunset and commences shortly after. Attack frequency is low on overcast days or at temperatures below 22 and above 32 ºC. On livestock, biting occurs on the abdomen, legs, and neck. Tabanids inflict deep wounds that cause a flow of blood. The mandibles and maxillae penetrate the skin in a scissor-like action. Anticoagulants in the saliva are pumped into the wound and the blood is ingested through the sponging labella. Pathogens may be transmitted from flies that are disturbed while feeding on one animal and begin feeding on another. It is known that deer flies can mechanically vector Tularemia and Loa loa, and horse flies transmit Anthrax. Fly attacks result in lowered gains and low milk production in livestock animals. In 1976, estimated losses in the United States were at 40 million dollars. One cattle ranch in Kentucky lost an average 100 lbs. per animal due to tabanids. It is not uncommon to see as many as 100 flies feeding on an animal at one time. Twenty to thirty flies feeding for six hours are capable of taking 100 cc of blood.
There are no effective biological control programs for controlling tabanids. There are native beneficial insects that target tabanids. Eggs are parasitizied by such Hymenoptera families as Trichogrammatidae, Scelionidae and Chalcididae. Diapriidae and Pteromalidae (Hymenoptera) and Bombyliidae and Tachinidae (Diptera) parasitize the larvae and pupa. Tabanid adults are used as provisions for nest building wasps. Cattle egrets and killdeer are also tabanid feeders.
This cache has been placed with permission for the CREW Trust and
the South Florida Water Management District
Good luck!