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Tabanus similis

What do they look like?

Tabanus similis is a fly with a black body, and long, clear wings. Males and females of this species look different. Females have a black abdomen with yellow or orange stripes, while males have much less black or no black at all. Males also have skinnier antennae, while females have different mouthparts. Both males and females have large, bright green and brown striped eyes. (Teskey, 1990; Thomas, 2011)

  • Sexual Dimorphism
  • sexes colored or patterned differently
  • sexes shaped differently
  • ornamentation
  • Range length
    11 to 17 mm
    0.43 to 0.67 in

Where do they live?

Tabanus similis, a species of horse fly, lives in the northern half of the United States and southern regions of eastern Canada. (McAlpine, et al., 1981; Teskey, 1990)

What kind of habitat do they need?

The larvae of T. similis are aquatic and live in lakes, rivers and streams. Adults are found on land near the lakes and rivers, in forests, grasslands, farmlands, cities, and suburban areas. (Krčmar and Mikuška, 2012; Merritt, et al., 2008; Teskey, 1990)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams

How do they grow?

Horse flies go through complete metamorphosis, and have the life stages of egg, larva, pupa, and adult. After mating, females lay the eggs in layers on rocks or plants that hang out over water. The eggs hatch in about 7 days, but this can depend on the temperature. They hatch faster in warmer temperatures, but take longer in colder temperatures. All the eggs hatch at once, and the larvae fall into the water below. They dig down into the dirt at the bottom of the water and stay there as larvae for 1 to 3 years. When they emerge, they become pupae. They stay as pupae for about two weeks, and then become adults. Larvae are a whitish color, and pupae are yellowish. (Hays, 1956; Hine, 1903)

How do they reproduce?

When looking for mates, male horse flies are often seen on the tops of hills or wooded areas where females may also be. These males may be in small groups or alone, and they hover near the ground or near plants. When a female flies by, the male chases after her. Often the females reject the males and do not want to mate. If the female does want to mate, they will mate for about 30 minutes. Mating occurs during warm, clear weather during summer. Some females only mate once in their lives. (Teskey, 1990; Thornhill and Alcock, 1983; Yuval, 2006)

Female horse flies are parasites and have to feed on blood from a mammal before they can lay their eggs. After they feed, females lay the eggs on surfaces like rocks or plants hanging over water sources, like a river or pond. Males often rest on plants nearby while females are laying eggs. (Hine, 1903)

  • How often does reproduction occur?
    Tabanus similis breeds once per year.
  • Breeding season
    Mating takes place in the summer.

Tabanus similis puts nutrients in the eggs for the offspring to grow and develop before hatching. The females also lay the eggs on surfaces hanging out over water so that the larvae can drop into the water and have somewhere to live after hatching. Horse flies leave their eggs after laying them and do not provide any more care. (Hays, 1956; Hine, 1903; Teskey, 1990)

  • Parental Investment
  • pre-hatching/birth
    • provisioning

How long do they live?

The larval stage for Tabanus similis can last for 1 to 3 years. Adults do not live for very long after emerging from pupation, only for about a month. (Hays, 1956; Hine, 1903)

  • Typical lifespan
    Status: wild
    3 (high) years

How do they behave?

Tabanus similis is active from early June to mid August. Female horse flies are parasites, and can often been seen flying around large mammals and humans while buzzing loudly. They may do this alone or gather in large groups. They occasionally land on low plants or on the ground and are most active in the sunlight on calm days. (Askew, 1971; Hine, 1903; Teskey, 1990)

Home Range

Horse flies stay near bodies of water where they can lay their eggs. (Krčmar and Mikuška, 2012)

How do they communicate with each other?

Female horse flies are attracted to dark, moving objects. They also detect carbon dioxide to find mammals to feed on their blood. Males and females identify each other by sight when a male is searching for a female mate. (Horvath, et al., 2010)

  • Communication Channels
  • visual

What do they eat?

Horse fly larvae are predators and feed on small, soft-bodied organisms in the water. Adult females are parasites and feed on blood from large mammals, such as horses and cattle. Tabanus similis sometimes feeds on humans, but it is not as common for this species of horse fly. Adult males feed on nectar from flowers. (Askew, 1971; Cobb and Balsbaugh, 1976; Hine, 1903; Merritt, et al., 2008; Mohamed-Ahmed and Mihok, 2009; Smith, et al., 1970)

  • Animal Foods
  • blood
  • insects
  • Plant Foods
  • nectar

What eats them and how do they avoid being eaten?

Predators of Tabanus similis include birds, dragonflies, robber flies, and wasps. (Merritt, et al., 2008; Teskey, 1990)

What roles do they have in the ecosystem?

Tabanus similis has a variety of roles in its ecosystem. Horse fly larvae are predators of small aquatic organisms. Adult females are parasites, and must feed on blood from large mammals before reproducing. Males may help pollinate flowers while they feed on nectar. Tabanus similis is eaten by variety of animals, including birds and other insects. Some wasp species are parasites of the eggs of many horse fly species. The wasps lay their eggs inside the horse fly eggs, which kills the horse fly. (Carn, 1996; Hine, 1903; Merritt, et al., 2008)

Species (or larger taxonomic groups) used as hosts by this species
  • horses, Equus ferus caballus
  • cattle, Bos primigenius
  • humans, Homo sapiens
Commensal or parasitic species (or larger taxonomic groups) that use this species as a host

Do they cause problems?

Horse fly females can transmit diseases to the mammals they bite. Their bites are painful, so they often do not finish their blood meal before the animal being bitten brushes the flies off. This means that the horse flies have to feed from several different animals before they are finished, and this allows them to infect many different animals. They can transmit diseases like Hog Cholera Virus (HCV) in livestock and anthrax in humans. Since some of the animals they bite are horses and cows, this can cause economic losses for farmers. (Askew, 1971; Carn, 1996)

How do they interact with us?

There horse flies do not have any positive effects on humans.

Are they endangered?

Tabanus similis is not an endangered species.


Heather Williams (author), University of Michigan Biological Station, Brian Scholtens (editor), University of Michigan Biological Station, Angela Miner (editor), Animal Diversity Web Staff.


Askew, R. 1971. Parasitic Insects. London, England: Heinemann Educational Books Ltd.

Carn, V. 1996. The Role of Dipterous Insects in the Mechanical Transmission of Animal Viruses. British Veterinary Journal, 152, 377: 385-387.

Cobb, P., E. Balsbaugh. 1976. The Tabanidae (Diptera) of Spink County, South Dakota. Journal of the Kansas Entomological Society, 49, 4: 519.

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

Hine, J. 1903. Tabanidae of Ohio with a Catalogue and Bibliography of the Species from America North of Mexico. Columbus, Ohio: Press of Spahr and Glenn.

Horvath, G., M. Blaho, G. Kriska, R. Hegedus, B. Gerics, R. Farkas, S. Akesson. 2010. An Unexpected Advantage of Whiteness in Horses: the Most Horsefly-Proof Horse has a Depolarizing White Coat. Proceedings of the Royal Society of Biological Sciences, 277: 1643-1650.

Krčmar, S., A. Mikuška. 2012. Distribution of Halophilous Species of Horse Flies in Croatia (Diptera: Tabanidae). Aquatic Insects: International Journal of Freshwater Entomology, 34, 1: 3-10.

McAlpine, J., B. Peterson, G. Shewell, H. Teskey, J. Vockeroth, D. Wood. 1981. Manual of Nearctic Diptera. Ottawa, Ontario: Biosystematics Research Institute.

Merritt, R., K. Cummins, M. Berg. 2008. An Introduction to the Aquatic Insects of North America. Dubuque, Iowa: Kendall/Hunt Publishing Company.

Mohamed-Ahmed, M., S. Mihok. 2009. Alighting of Tabanidae and Muscids on Natural and Simulated Hosts in the Sudan. Bulletin of Entomological Research, 99: 569.

Smith, S., D. Davies, V. Golini. 1970. A Contribution to the Bionomics of the Tabanidae (Diptera) of Algonquin Park, Ontario: Seasonal Distribution, Habitat Preferences, and Biting Records. The Canadian Entomologist, 102: 1461-1462.

Teskey, H. 1990. The Insects and Arachnids of Canada. The Horse Flies and Deer Flies of Canada and Alaska, Diptera: Tabanidae. Ottawa, Ontario: Biosystematics Research Centre.

Thomas, A. 2011. Tabanidae of Canada, East of the Rocky Mountains 2: A Photographic Key to the Genera and Species of Tabaninae (Diptera: Tabanidae). Canadian Journal of Arthropod Identification, 13: 448-451.

Thornhill, R., J. Alcock. 1983. The Evolution of Insect Mating Systems. Cambridge, Massachusetts, and London, England: Harvard University Press.

Yuval, B. 2006. Mating Systems of Blood-Feeding Flies. Annual Review of Entomology, 51, 1: 423-425.

University of Michigan Museum of ZoologyNational Science Foundation

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Williams, H. 2014. "Tabanus similis" (On-line), Animal Diversity Web. Accessed February 23, 2024 at

BioKIDS is sponsored in part by the Interagency Education Research Initiative. It is a partnership of the University of Michigan School of Education, University of Michigan Museum of Zoology, and the Detroit Public Schools. This material is based upon work supported by the National Science Foundation under Grant DRL-0628151.
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