Tabanus atratus

Geographic Range

Tabanus atratus is primarily found in the eastern United States, although it has been collected throughout the entire continental US.

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

This horsefly is able to survive in a wide range of habitats although it cannot survive in extreme climates such as mountain tops or deserts. It requires moist environments in which to lay eggs, and mammals to feed on.

• Terrestrial Biomes
• savanna or grassland savanna or grassland
• chaparral chaparral
• forest forest

• Other Habitat Features
• suburban suburban
• agricultural agricultural

Physical Description

Adults of this species reach 20-25 mm in length. The flies can be entirely black, including the wings, or dark brown to blackish purple. Tabanus atratus have large compound eyes, which are dichoptic (separated) in females, and holoptic (continuous) in males. They have prominent mouthparts, which are easily distinguishable: The fascicle is made of six piercing organs. Starting from the outside, there are 2 flattened, bladelike mandibles with tooth like serrations used for cutting. Two narrow maxillae also serrated used to pierce the tissue and blood vessels of the host, a median hypopharynx and a median labrum-epipharynx. The hypopharynx and labrum-epipharynx make up the food canal, while the labrum is a large sponge like organ used to lap up blood (Roberts and Janovy, 2000). Short stout hairs cover the body, and wing venation is pronounced.

Larva of Tabanus atratus are similar to the larvae of all other horseflies. Larvae can be white to tan, while possessing a slender, cylindrical body, which tapers at the head. (Strother, 2000) Like other tabanids, the larva of the black horsefly has twelve segments and a retractable tracheal siphon used for respiration. The retractable head of the larva has two sharp mandibles that can cause a painful bite (Roberts and Janovy, 2000). The pupae have a series of spines sticking out from the abdominal segments, and usually exhibit little movement (Hutchinson, 1999).

• Other Physical Features
• ectothermic ectothermic
• heterothermic heterothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes shaped differently

Development

Horse flies pass through the following holometabolous life stages: egg, larva, pupa, and adult. After the eggs hatch, the larvae will drop down into water or burrow into a moist environment where it then matures through six to nine instars before pupation (Hutchinson, 1999). In colder climates, larvae will overwinter, then move to drier soil to in order to pupate (Strother, 2000). The pupal stage lasts from one to three weeks.

• Development - Life Cycle
• metamorphosis metamorphosis

Reproduction

Tabanus atratus generally breed near aquatic environments. When the adult fly emerges, mating occurs. Females then search for a blood meal, while males feed on nectar.

Each female will lay three to four masses of one hundred to a thousand eggs each, in layers near water's edge or somewhere quite close to water.

• Key Reproductive Features
• iteroparous iteroparous
• sexual sexual
• fertilization fertilization
  • internal internal
• oviparous oviparous

After searching for and laying eggs in a suitable environment for larvae to grow and develop, there is no further parental involvement.

• Parental Investment
• pre-fertilization
  • provisioning
  • protecting
    • female

Behavior

Horseflies are active during the daytime, and once a host is found, the horsefly will attack relentlessly in order to feed (Strother, 2000). Adult flies can fly over 65 kilometers, but will generally not disperse more than 2 miles away from where they emerged. The flies rest on paths and roads, especially in wooded areas. Whenever the wind picks up or temperature drops, a significant decrease in flies can be observed. Tabanus atratus is also attracted to light, commonly congregating at light sources during the night (Greenvalley, 2000).

• Key Behaviors
• flies
• diurnal diurnal
• motile motile

Food Habits

The females of T. atratus feed on mammalian blood, while males, which lack mandibles, feed on nectar and plant juices (Hutchinson, 1999). A blood meal is necessary in order for females to nourish their developing eggs (Strother, 2000). Horseflies are diurnal, usually feed during the day (Greenvalley, 2000). The mouthparts are made of six piercing organs: two mandibles; two maxillae; hypopharynx; and a labrum-epipharynx. The mandibles and the maxillae have sharp serrated teeth on them, which are used for puncturing the skin and rupturing blood vessels (Roberts and Janovy, 2000). The labrum then functions to lap up the pool of blood that is formed from the bite, otherwise known as telmophagy (Hutchinson, 1999). When searching for a host, females are attracted to large, dark, moving objects and to CO2. Larvae feed voraciously on other insect larvae, other invertebrates and small vertebrates (Strother, 2000).

• Primary Diet
• carnivore carnivore
  • sanguivore sanguivore

• Animal Foods
• blood

Economic Importance for Humans: Positive

This species provides no major economic benefit to humans.

Economic Importance for Humans: Negative

Although Tabanus atratus do not often bite humans, when it does happen it leaves painful memories. This fly can also transmit bacterial, viral, and other diseases such as surra and anthrax, to both humans and other animals through its bite.

The effect of T. atratus on livestock can be a serious problem. Blood loss and irritation from the flies can severely affect beef and milk production, as well as grazing. Livestock usually have no way of avoiding the painful bites, and millions of dollars have been spent trying to control these pests.

• Negative Impacts
• injures humans
  • bites or stings
  • causes disease in humans causes disease in humans
  • carries human disease
• causes or carries domestic animal disease causes or carries domestic animal disease

Conservation Status

This species requires no special conservation status.

Additional Links

Encyclopedia of Life

Contributors

Sara Diamond (editor), Animal Diversity Web.

Wilson Long (author), University of Michigan-Ann Arbor, Barry OConnor (editor), University of Michigan-Ann Arbor.

References

Hays, K. 1956. A Synopsis of the Tabanidae (Diptera) of Michigan . Ann Arbor: University of Michigan. Museum of Zoology.

Hutchinson, R. 1999. "Horse Flies" (On-line). Accessed March 3, 2001 at http://www.roberth.u-net.com/ .

Roberts, L., J. Janovy Jr.. 2000. Foundations of Parasitology . Boston: The McGraw-Hill Companies, Inc..

Strother, S. 2000. Tabanids (horseflies). Dermatology Online Journal , 5(2): 6.

2000. "Welcome to the World of the Horseflies" (On-line). Accessed March 2, 2001 at http://www.greenvalleypc.com/frontpage.htm .