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Chrysops frigidus

What do they look like?

Chrysops frigidus has a small body compared to other deer flies. The front part of the head is yellow, the mouthparts are brown, and the antennae are brown or black. Their bodies are black and yellow. Their wings are clear with black or brown markings. Males have small differences in their antennae and mouthparts from females, and also have some darker areas in their wings than females. Some of these deer flies have much paler colors, but this is just a variety and they are still the same species.

The larva is 12 to 15 mm long, and pale yellow in color with a greenish tinge. The pupa is 11 to 12 mm long and light brown. (Teskey, 1969; Teskey, 1990; Thomas, 2009)

  • Sexual Dimorphism
  • sexes colored or patterned differently
  • Average length
    7-11 mm

Where do they live?

Chrysops frigidus is a deer fly found throughout Canada and Alaska and in the northeastern parts of the United States in New England. The most southern part of its range is the Rocky Mountains in Colorado. (Teskey, 1990; Thomas, 2009)

What kind of habitat do they need?

This deer fly is found in a variety of wetland habitats. It is most commonly seen in swampy woodlands. The larvae of the fly are also found in a wide variety of wetland habitats but have to live on a certain kind of moss. (Teskey, 1969; Teskey, 1990; Thomas, 2009)

How do they grow?

Deer flies have complete metamorphosis and have the life stages of egg, larva, pupa, and adult. Before a female can lay her eggs, she must feed on blood from another animal first. She lays her eggs in moist sheltered areas. This species uses a special moss. Eggs hatch after about 5 days, and the larvae live in the moss. The larvae go through 6 stages called instars. This takes about 9 to 10 months. The larvae then move to a more protected position and become pupae, which lasts about 2 weeks. Adults normally emerge in the morning and their wings soon expand and harden so that they can fly away. ("Tabanidae The horseflies", 2002; Lake and Burger, 1980; Magnarelli and Anderson, 1977; Magnarelli and Anderson, 1981; Roberts, 1980; Teskey, 1969; Teskey, 1990)

How do they reproduce?

Male deer flies fly around looking for females or sit on vegetation, chasing after any passing flies, including possible female mates. Mating likely happens in the morning when temperatures are cooler. Females likely mate at least two times during their lives. (Anderson, 1971; Catts and Olkowski, 1972; Goodwin and Drees, 1996; Leprince, et al., 1983; Teskey, 1990; Troubridge and Davies, 1975)

Before females can lay their eggs, they have to feed on blood from an animal. Four to eight days after the blood meal, females lay the fertilized eggs on the stems or underside of leaves above or near the moss that this species uses. The eggs are usually laid on warm, sunny days in the morning. Deer flies are good fliers and may move as far as 1 to 2 km from where they mated to lay their eggs. (Anderson, 1971; Catts and Olkowski, 1972; Goodwin and Drees, 1996; Leprince, et al., 1983; Magnarelli and Anderson, 1977; Teskey, 1990)

  • How often does reproduction occur?
    Females likely mate twice in their lives.
  • Breeding season
    Mating takes place from May to September.

Females feed on the blood of other animals to be able to provide yolk in the eggs for their offspring. They also lay the eggs near the the moss that this species uses. The adults move on after the eggs are gone and provide no more parental care. (Teskey, 1990)

  • Parental Investment
  • pre-hatching/birth
    • provisioning
      • female

How long do they live?

The lifespan of Chrysops frigidus is a little over a year, at most. Adults likely live for several weeks after emerging from pupation.

  • Typical lifespan
    Status: wild
    1 (high) years

How do they behave?

Deer fly females often gather in groups, especially when looking for an animal to feed on. They are very active and fly a lot, and can be seen flying around from late May to mid-September. They are the most active on warm, sunny days.

Females give painful bites to the animals that they are taking blood from. Because the bite is so painful, it is hard for the female deer flies to finish their blood meal before the animal brushes the fly away. So females have to take blood from several different animals, and they often spread diseases to the animals (and humans) that they bite. (Burnett and Hays, 1974; Krinsky, 1976; Teskey, 1990)

Home Range

Deer flies can fly up to 1 to 2 km away from where they emerged and mated.

How do they communicate with each other?

Deer flies use vision and detect chemicals to communicate with others, as well as to gather information about their environment. Males use vision to find mates, and females use vision to find animals to feed on blood from, and also to find places to find eggs. Females are attracted to chemicals produced by animal hosts. They are also attracted to sources of heat, which is one way that they find warm mammals to feed on. (Anderson, 1971; Catts and Olkowski, 1972; Leprince, et al., 1983; Mihok, et al., 2007; Teskey, 1990)

What do they eat?

The larvae apparently feed on organic matter in moist soil. Adult males feed mainly on nectar, but also on pollen. Females feed on nectar as well, but also eat rotting fruit and a sugary-liquid called honeydew produced by insects in the order Hemiptera. Adult females feed on blood to produce yolk for their eggs. They feed on blood from deer, humans, cattle, sheep, hogs, horses and other domestic animals. (Lewis and Leprince, 1981; Magnarelli and Anderson, 1977; Magnarelli and Anderson, 1980; Magnarelli and Anderson, 1981; McAlpine, et al., 1981; Teskey, 1990)

  • Animal Foods
  • blood
  • Plant Foods
  • fruit
  • nectar
  • pollen

What eats them and how do they avoid being eaten?

Deer flies of the genus Chrysops have been recorded as prey for birds, amphibians, dragonflies, robber flies, and wasps (including Vespula, Crabro, and Bembix). (Teskey, 1990)

What roles do they have in the ecosystem?

Chrysops frigidus males may pollinate the flowers on which they feed. They are also preyed upon by many other animals. Females are parasites and need to eat blood before they can reproduce. They feed on the blood of many large vertebrates, including deer, humans, and many domestic animals. The females can also transmit diseases to the animals they bite. These deer flies are also harmed by many different parasites. (Krinsky, 1976)

Species (or larger taxonomic groups) used as hosts by this species
Commensal or parasitic species (or larger taxonomic groups) that use this species as a host

Do they cause problems?

Deer flies are known as pests because the female will feed on the blood of certain mammals, including humans. Deer flies in this genus, Chrysops, are known to be able transmit diseases to the animals they bite, including anthrax, tularemia, anaplasmosis, hog cholera, equine infectious anemia and filariasis, and even Lyme disease. In North America, they do not cause many health problems for people, but their bites can be painful and annoying. They are responsible for causing disease in domestic animals and livestock, however. (Lewis and Leprince, 1981; Luger, 1990; Lyon, 2013; Magnarelli and Anderson, 1980)

How do they interact with us?

These deer flies may help to pollinate some plants that humans use, but otherwise they are not helpful to humans. (Teskey, 1990)

Are they endangered?

Chrysops frigidus is not an endangered species.

Some more information...


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


2002. "Tabanidae The horseflies" (On-line). Accessed August 07, 2013 at

Anderson, J. 1971. Autogeny and mating and their relationship to biting in the saltmarsh deer fly, Chrysops atlanticus (Diptera: Tabanidae). Ann. Entomol. Soc. Amer., 64/6: 1421-1424.

Burnett, A., K. Hays. 1974. Some influence of meteorological factors on flight activity of female horse flies (Diptera: Tabanidae). Environ. Entomol., 3: 515-521.

Catts, E., W. Olkowski. 1972. Biology of Tabanidae (Diptera): mating and feeding behavior of Chrysops fulliginosus. Environ. Entomol., 1/4: 448-453.

Goodwin, J., B. Drees. 1996. The horse and deer flies (Diptera: Tabanidae) of Texas. Southwestern Entomological Society, 20/3: 1-140.

Krinsky, W. 1976. Animal disease agents transmitted by horse-flies and deer flies (Diptera: Tabanidae). J. Medical Entomol., 13: 225-275.

Lake, D., J. Burger. 1980. Ovarian development in adult Chrysops (Diptera: Tabanidae) in northern New England, with emphasis on Chrysops ater and C. mitis. J. Medical Entomol., 17/6: 502-505.

Leprince, D., D. Lewis, J. Parent. 1983. Biology of male tabanids (Diptera) aggregated on a mountain summit in southwestern Quebec. J. Medical Entomol., 20: 608-613.

Lewis, D., D. Leprince. 1981. Horse flies and deer flies (Diptera: Tabanidae) feeding on cattle in southwestern Quebec. Canadian Entomologist, 113: 883-886.

Luger, S. 1990. Lyme Disease transmitted by a biting fly. New England Journal of Medicine, 322/24: 1752.

Lyon, W. 2013. "Horse and Deer Flies" (On-line). Accessed August 08, 2013 at

Magnarelli, L., J. Anderson. 1977. Follicular development in salt marsh Tabanidae (Diptera) and incidence of nectar feeding with relation to gonotrophic activity. Ann. Entomol. Soc. Amer., 70/4: 529-533.

Magnarelli, L., J. Anderson. 1981. Sugar feeding by female tabanids (Diptera: Tabanidae) and its relation to gonotrophic activity. J. Medical Entomol., 18/5: 429-433.

Magnarelli, L., J. Anderson. 1980. Feeding behavior of Tabanidae (Diptera) on cattle and serologic analyses of partial blood meals. Environ. Entomol., 9: 664-667.

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

Mihok, S., D. Carlson, P. Ndegwa. 2007. Tsetse and other biting fly responses to Nzi traps baited with octenol, phenols and acetone. Medical and Veterinary Entomol., 21: 70-84.

Proshek, B. 2007. "Species Page - Chrysops frigidus" (On-line). Entomology Collection. Accessed August 06, 2013 at

Roberts, R. 1980. The effect of temperature on the duration of oogenesis and embryonic development in Tabanidae (Diptera). J. Medical Entomol., 17/1: 8-14.

Teskey, H. 1969. Larvae and pupae of Tabanidae. Memoirs of the Entomological Society of Canada, 63: 1-147.

Teskey, H. 1990. The horse flies and deer flies of Canada and Alaska Diptera: Tabanidae. The Insects and Arachnids of Canada, 381: 1-End.

Thomas, A. 2009. Tabanidae of Canada, east of the Rocky Mountains 1: a photographic key to species of Chrysopinae and Pangoniinae (Diptera: Tabanidae). Canadian journal of arthropod identification, Unknown: Unknown.

Troubridge, D., D. Davies. 1975. Seasonal changes in physiological age composition of tabanid (Diptera) populations in southern Ontario. J. Medical Entomol., 12/4: 453-457.

University of Michigan Museum of ZoologyNational Science Foundation

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Gezon, N. 2014. "Chrysops frigidus" (On-line), Animal Diversity Web. Accessed April 17, 2024 at

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