Tabanus similis

Geographic Range

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


The larvae of T. similis have been found to occupy the substrates of various aquatic environments, including flowing and still waters. Adults are found in the terrestrial zones near these sources of water, in forests, grasslands, agricultural, urban and suburban areas. (Krčmar and Mikuška, 2012; Merritt, et al., 2008; Teskey, 1990)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams

Physical Description

Tabanus similis has significant sexual dimorphism. Females have a black abdomen with yellow or orange stripes and biting mouth parts, while males exhibit less or no black coloration and narrower antennae. Both sexes have large, bright green and brown striped eyes when they are alive. (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


Documented observation of various species of tabanid development is limited; however, known information regarding other species in the genus Tabanus can provide useful insight into the life history of T. similis. Eggs, which are deposited in layers on rocks or vegetation overhanging water, hatch in an average of seven days but can mature faster in warmer temperatures and slower in colder temperatures. All eggs in a mass usually hatch at the same time, and the larvae wiggle off their perch and into the water below, where they dig down into the substrate and remain until emerging as pupae. Most tabanid larvae persist for one to three years and pupae for about two weeks. Larvae are a whitish color, and pupae are yellowish. (Hays, 1956; Hine, 1903)


Mating occurs very soon after emergence as an adult in tabanids. In some species of horse flies in the genus Tabanus, males will frequent the tops of hills or wooded areas that are known for the presence of females. These males will present themselves alone or in small groups and hover near the ground or plant life waiting for a female to fly by. When she does, the male will pursue her, most likely to be rejected. If she is of the same species and does not reject the copulation, they will mate for an average of 30 minutes before feeding. This pairing happens during warm, clear weather and only once for some documented species of female tabanids. (Teskey, 1990; Thornhill and Alcock, 1983; Yuval, 2006)

After mating and taking a blood meal, females oviposit on surfaces like rocks or plants overhanging water sources. Males often rest on nearby vegetation during the process of oviposition. (Hine, 1903)

  • Breeding interval
    Tabanus similis breeds once per year.
  • Breeding season
    Mating takes place in the summer.

Tabanus similis provides provisioning in the eggs, and females also lay the eggs on surfaces overhanging water sources, so that the aquatic larvae will have a suitable habitat to drop into. Tabanids provide no further parental care. (Hays, 1956; Hine, 1903; Teskey, 1990)

  • Parental Investment
  • pre-hatching/birth
    • provisioning


The larval stage can last for one to three years in tabanids and the pupal stage about two weeks. Adults are short-lived and in most species persist for about a month. (Hays, 1956; Hine, 1903)

  • Typical lifespan
    Status: wild
    3 (high) years


Tabanus similis is active from early June to mid August. Female horse flies are parasitic, 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 are periodically observed landing on low foliage or on the ground and are most active in the sunlight on calm days. (Askew, 1971; Hine, 1903; Teskey, 1990)

Home Range

Tabanids remain near sources of water. (Krčmar and Mikuška, 2012)

Communication and Perception

Female tabanids are attracted to dark, moving objects and emissions of carbon dioxide as these help them identify potential hosts. Visual cues are also used to identify mates, as male flies hover about and chase after females that they see fly past. (Horvath, et al., 2010)

  • Communication Channels
  • visual

Food Habits

Larval horse flies use piercing mouthparts to consume small, soft-bodied organisms in the water. Adult females take blood meals usually from the legs of horses and cattle. Tabanus similis occasionally feeds on humans, though it is not as common for this species of horse fly. Blood meals are used for the production of eggs in females, but adult males consume the nectar of 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


Adults are preyed upon by birds, dragonflies, robber flies, and wasps. There are no known defenses of T. similis against predators. (Merritt, et al., 2008; Teskey, 1990)

Ecosystem Roles

Larval horse flies consume small, soft-bodies organisms in their aquatic habitats. Adult females are parasitic and must take blood meals from large mammals before reproducing. As nectar feeders, males may play a small role in pollinating the flowers from which they feed. Tabanus similis also serves as prey to a variety of animals, including birds and other insects. Some wasp species are parasites on the eggs of many horse fly species in the genus Tabanus. (Carn, 1996; Hine, 1903; Merritt, et al., 2008)

Species Used as Host
  • horses, Equus ferus caballus
  • cattle, Bos primigenius
  • humans, Homo sapiens
Commensal/Parasitic Species

Economic Importance for Humans: Positive

There is no known positive effects of Tabanus similis on humans.

Economic Importance for Humans: Negative

Due to their frequent tendency to bite mammals, horse flies are known vectors of disease like Hog Cholera Virus (HCV) in livestock and anthrax in humans. Due to the pain caused by their bites, mammals react by removing the pest, and tabanids are free to victimize other organisms with the blood of the first host still on their mouthparts. The decline in livestock has negative consequences for human agriculture and can cause significant economic loss. (Askew, 1971; Carn, 1996)

Conservation Status

There is no special conservation status for T. similis.


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



living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map


living in landscapes dominated by human agriculture.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


an animal that mainly eats meat

causes or carries domestic animal disease

either directly causes, or indirectly transmits, a disease to a domestic animal


Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.


uses smells or other chemicals to communicate

  1. active during the day, 2. lasting for one day.

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature


union of egg and spermatozoan


forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.


mainly lives in water that is not salty.


An animal that eats mainly plants or parts of plants.


having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

internal fertilization

fertilization takes place within the female's body


A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.


having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.


an animal that mainly eats nectar from flowers


reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.


an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death

polarized light

light waves that are oriented in particular direction. For example, light reflected off of water has waves vibrating horizontally. Some animals, such as bees, can detect which way light is polarized and use that information. People cannot, unless they use special equipment.


"many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph.


Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).


an animal that mainly eats blood

seasonal breeding

breeding is confined to a particular season


remains in the same area


offspring are all produced in a single group (litter, clutch, etc.), after which the parent usually dies. Semelparous organisms often only live through a single season/year (or other periodic change in conditions) but may live for many seasons. In both cases reproduction occurs as a single investment of energy in offspring, with no future chance for investment in reproduction.


reproduction that includes combining the genetic contribution of two individuals, a male and a female

sexual ornamentation

one of the sexes (usually males) has special physical structures used in courting the other sex or fighting the same sex. For example: antlers, elongated tails, special spurs.


living in residential areas on the outskirts of large cities or towns.


that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).


Living on the ground.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.


A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.


living in cities and large towns, landscapes dominated by human structures and activity.


uses sight to communicate


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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.

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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.

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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.