Deer flies (also known in some parts of the mid-Atlantic United States as sheep flies) are
bloodsucking insects considered
pests
PESTS was an anonymous American activist group formed in 1986 to critique racism, tokenism, and exclusion in the art world. PESTS produced newsletters, posters, and other print material highlighting examples of discrimination in gallery represent ...
to humans and cattle.
They are large flies with large brightly-coloured
compound eyes, and large clear wings with dark bands.
They are larger than the common
housefly
The housefly (''Musca domestica'') is a fly of the suborder Cyclorrhapha. It is believed to have evolved in the Cenozoic Era, possibly in the Middle East, and has spread all over the world as a commensal of humans. It is the most common fl ...
and smaller than the
horse-fly. There are 250 species of deer fly in the genus ''Chrysops''. Their distribution is worldwide, though they have not been reported in
Iceland,
Greenland, and
Hawaii.
Deer flies lay between 100 and 800 eggs in batches on vegetation near water or dampness. During the larval stage, which lasts one to three weeks, they feed on small creatures or rotting organic matter near or in the water.
After a pupal stage, they emerge as adults in late spring and summer. While male deer flies collect
pollen
Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametophyt ...
, female deer flies feed on
blood, which they require to produce eggs.
Females feed primarily on mammals. They are attracted to prey by sight, smell, or the detection of
carbon dioxide. Other attractants are body heat, movement, dark colours, and lights in the night. They are active under direct sunshine and hours when the temperature is above 22 °C (71.6°).
When feeding, the females use scissor-like
mandibles and
maxillae to make a cross-shaped incision and then lap up the blood. Their bite can be painful. Anti-coagulants in the saliva of the fly prevents blood from clotting and may cause severe allergic reactions. Parasites and diseases transmitted by the deer fly include
tularemia,
anthrax
Anthrax is an infection caused by the bacterium ''Bacillus anthracis''. It can occur in four forms: skin, lungs, intestinal, and injection. Symptom onset occurs between one day and more than two months after the infection is contracted. The sk ...
,
anaplasmosis,
equine infectious anemia,
hog cholera, and
filiariasis.
DEET
''N'',''N''-Diethyl-''meta''-toluamide, also called DEET () or diethyltoluamide, is the most common active ingredient in insect repellents. It is a slightly yellow oil intended to be applied to the skin or to clothing and provides protection ag ...
is not an effective repellent.
Predators of the deer fly (and other Tabanidae) include nest-building wasps and hornets, dragonflies, and some birds, including the
killdeer. Deer flies are difficult to control because insecticides cannot be applied in the sensitive wetlands where their larvae typically develop. Additionally, adults may have developed a significant distance from where the eggs were laid.
Trapping devices and protective clothing, such as long-sleeved shirts and hats, can help avoid the annoyance and bites of aggressive deer flies.
Photos
File:Chrysops caecutiens-s.jpg,
File:Deerfly 8.jpg, Deerfly from coastal Georgia, US
References
External links
Penn State University's Deer Fly site
{{Taxonbar, from=Q1434069
Tabanidae
Brachycera genera
Taxa named by Johann Wilhelm Meigen
Diptera of North America
Diptera of South America
Diptera of Europe
Diptera of Asia
Diptera of Africa
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