Chrysops frigidus

Geographic Range

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


Chrysops frigidus is found in a variety of wetland habitats. It is most commonly collected in swampy woodlands. The larvae of the fly are also found in a wide variety of wetland habitats but are obligate to a moss substrate. (Teskey, 1969; Teskey, 1990; Thomas, 2009)

Physical Description

Chrysops frigidus has a relatively small body size compared to other Chrysops. It typically has a yellow frons, darkening at the vertex. The palps are brown. The first antennal segment is brown and the rest are a darker shade of brown or black. On the dorsum of the abdomen the first tergite has a dark middorsal rectangle surrounded by yellow. The first tergite also contains a median lunate black mark below the scutellum; this black mark narrowly reaches the hind margin of tergite 1 and meets a broader than long, posteriorly emarginate black figure on tergite 2. The remaining tergites are black with narrow paler hind margins. Males differ from females in that they have a moderately swollen scape, wider than the flagellum, a clypeal pruinose stripe that is complete to the oral margin, and wings with greater pigmentation in particular cells. The paler extreme of coloration was described as C. frigidus xanthas, but this variant occurs in many populations of the typical form across the country so it is not currently recognized as more than a variety.

The larva is 12 to 15 mm long, pale yellow in color with a greenish tinge. It has pubescence typical of other members of the genus, but only has minute lateral patches of pubescence on the preanal segment and 1 to 3 small pubescent spots on the lateral surfaces of the anal segment. The pupa is 11 to 12 mm long and light brown. The antennal ridges are small compared to other species. All sclerites of segments 2 to 7 have spinous fringes except the sterna on segments 2 to 5. (Teskey, 1969; Teskey, 1990; Thomas, 2009)

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


Deer flies are holometabolous and progress through egg, larval, pupal and adult stages. A blood meal is necessary for egg production. Chrysops frigidus is autogenous, and can lay one batch of eggs without a blood meal. Nectar feeding by females of some species may be a significant factor affecting the yolking of eggs and female success. Little specific information on the development of Chrysops frigidus is available. Tabanidae in general lay their eggs in sheltered moist areas with Chrysops frigidus in particular using moss substrates. Eggs are laid attached to each other and to a substrate (over or near water) in masses of less than 100 eggs. Embyronic development is usually complete in about 5 days. Almost all eggs hatch simultaneously after some warming by the sun. Larvae inhabit the soil or stream bed below and pass through approximately 6 instars. It is known that the growth of the larva happens far enough underground that larvicide treatments are ineffective. Larval development takes about 9 to 10 months. The larvae then migrate to a position where they will not be submerged for extended periods and pupate. The pupal period lasts about 2 weeks. Adults normally emerge from pupal cases in the morning and their wings soon expand and harden, making flight possible. ("Tabanidae The horseflies", 2002; Lake and Burger, 1980; Magnarelli and Anderson, 1977; Magnarelli and Anderson, 1981; Roberts, 1980; Teskey, 1969; Teskey, 1990)


Little is known about the specific mating behavior of this species but in other Chrysops species, males use either a hovering or non-hovering flight behavior as they seek mates. This has been most extensively studied in the salt marsh species C. atlanticus and C. fuliginosus. Most deer fly species use a strategy of waiting on nearby vegetation and then flying out after any passing flies, including potential female mates. In the salt marsh species, mating occurred mainly in the morning at cooler temperatures, before oviposition and feeding later in the day, at higher temperatures. Some research suggests that females may mate at least two times during their adult lifespan. In most Tabanidae species, the male to female sex ratio is 1:1. (Anderson, 1971; Catts and Olkowski, 1972; Goodwin and Drees, 1996; Leprince, et al., 1983; Teskey, 1990; Troubridge and Davies, 1975)

Females generally take about 4 to 8 days after a blood meal to mature a batch of eggs. These are laid as a group, usually on the stems or underside of leaves above or near a moss susbtrate. They are usually laid on warm, sunny days in the morning. Both males and females are known to take nectar meals for an energy source, and this seems to be an important source of nutrition. Tabanids are good fliers and may move as far as 1 to 2 km from their breeding sites to deposit egg masses. (Anderson, 1971; Catts and Olkowski, 1972; Goodwin and Drees, 1996; Leprince, et al., 1983; Magnarelli and Anderson, 1977; Teskey, 1990)

  • Breeding interval
    Females likely mate twice in their lives.
  • Breeding season
    Mating takes place from May to September.

The females provide provisioning in their eggs, and also lay their eggs in the specific moss habitat that allows the larvae to survive best. The adults then move on and provide no further care. (Teskey, 1990)

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


Chrysops frigidus hatches from eggs in summer, overwinters as a larva, emerges from the pupa in early summer and dies in late summer. Lifespan is a little over a year, at most. Little is known about the longevity of individuals as adults, but they are known to live for a number of weeks.

  • Typical lifespan
    Status: wild
    1 (high) years


There is little information available about the behavior of Chrysops frigidus. Tabanidae females, specifically Chrysops, typically occur in groups especially when seeking a blood meal. They are very active organisms, flying a considerable amount. The seasonal activity of adult deer flies normally extends from late May to mid-September. Activity is the greatest on sunny days with little or no wind. Several variables are known to affect activity including barometric pressure, temperature, cloud cover, and relative humidity. The females of the species actively seek warm-blooded mammals, such as deer and people in order to get a blood meal to nourish their eggs. Because a bite is painful, blood meals are often interrupted by avoidance behaviors of hosts. To complete a meal, females must feed on multiple host individuals, promoting the spread of disease among the host species. Various tabanids in North America are known to be vectors of tularemia, equine infectious anemia, vesicular stomatitis, hog cholera, encephalitis, anaplasmosis, trypanosomiasis, and filarial dermatosis of sheep. (Burnett and Hays, 1974; Krinsky, 1976; Teskey, 1990)

Home Range

Tabanid flies will disperse 1 to 2 km from their breeding sites.

Communication and Perception

Although Chrysops frigidus has not been studied, tabanids in general use both visual and chemical cues to perceive their environment and communicate with other individuals. Males use vision to help locate mates, and females use vision during their search for hosts and oviposition locations.

Chemicals are obviously part of the attraction that females have to hosts, because traps baited with carbon dioxide or octenol are known to attract feeding females. Females also see attracted thermally to potential hosts. They are especially attracted to dark surfaces, and black ball traps are regularly used to collect individuals. (Anderson, 1971; Catts and Olkowski, 1972; Leprince, et al., 1983; Mihok, et al., 2007; Teskey, 1990)

Food Habits

The larvae apparently feed on organic matter in moist soil but their specific feeding habits are unknown. Adult males feed on nectar (which is their primary energy source) and pollen. Females feed on nectar as a major energy source, but also use honeydew secreted by Hemiptera and rotting fruit. Adult females feed on blood to yolk eggs, using a variety of vertebrates. Deer and humans are frequently targeted, but cattle, sheep, hogs, horses and other domestic animals are also frequent hosts. (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


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)

Ecosystem Roles

Chrysops frigidus males may pollinate the flowers on which they feed. They are also food for other animals. Females are parasites and require a blood meal to reproduce. They feed on the blood of many large vertebrates, including deer, humans, and many domestic animals. The females can also transmit diseases to their hosts. Chrysops frigidus also serves as a host to a large variety of parasites. (Krinsky, 1976)

Species Used as Host
Commensal/Parasitic Species

Economic Importance for Humans: Positive

Chrysops frigidus have no described benefits to humans. It is possible that adults feeding on flower nectar may provide pollination services. (Teskey, 1990)

Economic Importance for Humans: Negative

Deer flies are known as pests because the female will feed on the blood of certain mammals, especially humans. Chrysops are known to be potential vectors for anthrax, tularemia, anaplasmosis, hog cholera, equine infectious anemia and filariasis. Tabanid flies may also be an occasional vector of Lyme Disease. The direct impact on humans in North America is mainly as an annoyance, but serious damage can result in domestic animals, due to biting and disease transmission. (Lewis and Leprince, 1981; Luger, 1990; Lyon, 2013; Magnarelli and Anderson, 1980)

Conservation Status

This species is abundant and requires no special conservation status.

Other Comments

Very little information is available about this species. Most information here is from studies on other species in the genus Chrysops.


Nicholas Gezon (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

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.


a wetland area rich in accumulated plant material and with acidic soils surrounding a body of open water. Bogs have a flora dominated by sedges, heaths, and sphagnum.

causes or carries domestic animal disease

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


uses smells or other chemicals to communicate


an animal that mainly eats decomposed plants and/or animals


particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).


a period of time when growth or development is suspended in insects and other invertebrates, it can usually only be ended the appropriate environmental stimulus.

  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.


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.


the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.


(as keyword in perception channel section) This animal has a special ability to detect heat from other organisms in its environment.

internal fertilization

fertilization takes place within the female's body


offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).


marshes are wetland areas often dominated by grasses and reeds.


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


the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.


"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.

seasonal breeding

breeding is confined to a particular season


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


lives alone


a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.


uses touch to communicate


Coniferous or boreal forest, located in a band across northern North America, Europe, and Asia. This terrestrial biome also occurs at high elevations. Long, cold winters and short, wet summers. Few species of trees are present; these are primarily conifers that grow in dense stands with little undergrowth. Some deciduous trees also may be present.


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.


uses sight to communicate


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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.

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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.