Chrysops excitans

Geographic Range

Chrysops excitans is a common and widespread deer fly, occurring across Canada and Alaska, south to California (as an isolated population) in the west and New Jersey and West Virginia in the east. (Teskey, 1990; Thomas and Marshall, 2009)


Chrysops excitans larvae are aquatic and are found close to shore in both lentic and lotic waters, such as lakes, ponds, swamps, marine beaches, and rivers. Adults occur in the forests, grasslands, taiga, and mountains near the aquatic habitats from which they emerged. (Merrit, et al., 2008)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams

Physical Description

Chrysops excitans is a medium sized fly (9 to 12 mm) with a mostly black body. Males are holoptic (eyes touch) and females have eyes separated on the head. The clypeus is black with a yellow, pruinose stripe. The wings have a characteristic black marking mid-wing which does not reach the posterior margin and a clear wing apex. The abdomen has dorsal median triangles which are especially large on the second segment. The second and third abdominal segments are often largely yellow or orange. This species is most easily confused with Chrysops dawsoni, from which it can be distinguished by the yellow triangle on the second abdominal segment. The female's mouthparts are specialized for biting and consist of a labium, a pair each of sharp, knife-like maxillae and mandibles, a hypopharynx and a labrum.

The eggs are fusiform and approximately 2 mm long. Larvae are tapered at both ends and have 11 segments. The first seven abdominal segments have a pair of dorsal, lateral and ventral prolegs. The pupae are obtect with the head, thorax, abdomen and appendage sheaths distinct. (Bland and Jacques, 1978; McAlpine, et al., 1981; Teskey, 1969; Teskey, 1990; Thomas and Marshall, 2009)

  • Sexual Dimorphism
  • sexes shaped differently
  • Range length
    9 to 12 mm
    0.35 to 0.47 in


Deer flies are holometabolous and progress through egg, larval, pupal and adult stages. A blood meal is necessary for egg production. Lake & Burger (1980) found that some species, including C. excitans seem to be anautagenous, and probably need a blood meal even to mature the first batch of eggs. Other species, including C. ater are autogenous, and can lay one batch of eggs without a blood meal. Results from Magnarelli (1976) differed for C. ater, indicating that there may be some population variation in this characteristic. Magnarelli & Anderson (1977, 1981) also found that nectar feeding by females of some species may be a significant factor affecting the yolking of eggs and female success. 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 water below and pass through approximately 6 instars. Larval development is 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 form pupal cases in the morning and their wings soon expand and harden, making flight possible. (Lake and Burger, 1980; Magnarelli and Anderson, 1977; Magnarelli and Anderson, 1981; Magnarelli, 1976; Roberts, 1980; Teskey, 1990)


There is no available information on 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. Leprince, Lewis & Parent (1983) studied male behavior in a variety of Chrysops species (not including C. excitans) in Quebec and found that all species used 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 work suggests that females may mate at least two times during their adult lifespan. (Anderson, 1971; Catts and Olkowski, 1972; Leprince, et al., 1983; 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 water. 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. (Anderson, 1971; Catts and Olkowski, 1972; Leprince, et al., 1983; Magnarelli and Anderson, 1977; Teskey, 1990)

  • Breeding interval
    Females seem to mate periodically over the course of the summer, with a blood meal between each mating.
  • Breeding season
    Breeding takes place from early June to the end of August.

Females of Chrysops excitans take blood meals to provide yolk and provisioning in the eggs. They also lay the eggs in a spot over suitable habitats for the larvae to drop into. Otherwise, they do not provide any other parental care. (Magnarelli and Anderson, 1977; Magnarelli and Anderson, 1981; Magnarelli and Anderson, 1977; Magnarelli and Anderson, 1981)

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


Chrysops excitans will hatch from eggs in summer, overwinter as larvae, emerge from pupae in early summer and die late summer. Lifespan is a little over a year, at most. Little is know about the longevity of individuals as adults, but they are known to live for a number of weeks. (Teskey, 1990)

  • Typical lifespan
    Status: wild
    1 (high) years


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 major activity of interest in this species is biting by females for blood meals. 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. (Burnett and Hays, 1974; Krinsky, 1976)

Home Range

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

Communication and Perception

Although Chrysops excitans 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 CO2 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 targets. (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


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

Ecosystem Roles

Chrysops excitans males may pollinate the flowers on which they feed. They are also food for other animals. Females are ectoparasites and require blood meals from a variety of vertebrates to mature their eggs. They feed on deer, humans, cattle, sheep, hogs, horses and other domestic animals. As blood feeders, they can also transmit disease to their hosts. Chrysops excitans is also used as a host to a variety of parasites. (Krinsky, 1976)

Species Used as Host
Commensal/Parasitic Species

Economic Importance for Humans: Positive

Plant pollination may occur as a result of the feeding habits (pollenophagy) of adult flies, but this is certainly minimal.

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 is known to be potential vectors for anthrax, tularemia, anaplasmosis, hog cholera, equine infectious anemia and filariasis (Lyon 2013). 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 status.


Brian Steel (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.


an animal that mainly eats meat

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.


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.


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.


This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

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.


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


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.

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.


uses sight to communicate


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