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 A compound eye is a visual organ found in arthropods such as insects and crustaceans. It may consist of thousands of ommatidia, which are tiny independent photoreception units that consist of a cornea, lens, and photoreceptor cells which distin ...

, 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 Horse-flies or horseflies are true Fly, flies in the family Tabanidae in the insect Order (biology), order Diptera. They are often large and agile in flight, and only the female horseflies bite animals, including humans, to hematophagy, obtai ...

. There are 250 species of deer fly in the genus ''Chrysops''. Their distribution is worldwide, though they have not been reported in

Iceland Iceland ( is, Ísland; ) is a Nordic island country in the North Atlantic Ocean and in the Arctic Ocean. Iceland is the most sparsely populated country in Europe. Iceland's capital and largest city is Reykjavík, which (along with its s ...

Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland is t ...

, and

Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only stat ...

. 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 Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the c ...

, 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 Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...

. 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 In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

and

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The t ...

e 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 Tularemia, also known as rabbit fever, is an infectious disease caused by the bacterium ''Francisella tularensis''. Symptoms may include fever, skin ulcers, and enlarged lymph nodes. Occasionally, a form that results in pneumonia or a throat infe ...

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 Anaplasmosis is a tick-borne disease affecting ruminants, dogs, and horses, and is caused by ''Anaplasma'' bacteria. Anaplasmosis is an infectious but not contagious disease. Anaplasmosis can be transmitted through mechanical and biological vector ...

equine infectious anemia Equine infectious anemia or equine infectious anaemia (EIA), also known by horsemen as swamp fever, is a horse disease caused by a retrovirus (''Equine infectious anemia virus'') and transmitted by bloodsucking insects. The virus (''EIAV'') is en ...

hog cholera Classical swine fever (CSF) or hog cholera (also sometimes called pig plague based on the German word ) is a highly contagious disease of swine (Old World and New World pigs). It has been mentioned as a potential bioweapon. Clinical signs Sw ...

, 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 The killdeer (''Charadrius vociferus'') is a large plover found in the Americas. It was described and given its current scientific name in 1758 by Carl Linnaeus in the 10th edition of his ''Systema Naturae''. Three subspecies are described. Th ...

. 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 de:Goldaugenbremse nl:Goudoogdaas