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Horse Botfly Imago.png
Horse botfly (Gasterophilus intestinalis)
Scientific classification e
Kingdom: Animalia
Clade: Euarthropoda
Class: Insecta
Order: Diptera
Suborder: Brachycera
Infraorder: Muscomorpha
Section: Schizophora
Subsection: Calyptratae
Superfamily: Oestroidea
Family: Oestridae

The Oestridae are a family of flies variously known as bot flies, warble flies, heel flies, gadflies, and similar names. Their larvae are internal parasites of mammals, some species growing in the host's flesh and others within the gut. The human botfly, Dermatobia hominis, is the only species of bot fly known to parasitize humans routinely, though other species of flies do cause myiasis in humans. The Human Botfly occurs in both Central and South America. A full grown female creates 1,000 eggs in her lifetime while laying 30 at a time. [1] Tourists have also been in contact in Southern Mexico as well as heavily forested areas.[2]


Deer bot fly (Cephenemyia stimulator)

A botfly,[3] also written bot fly,[4] bott fly[5] or bot-fly[6] in various combinations, is any fly in the family Oestridae. Their life cycles vary greatly according to species, but the larvae of all species are internal parasites of mammals. Largely according to species, they also are known variously as warble flies, heel flies, and gadflies. Asa Fitch, famous entomologist of his time suggested to name the cuterebra the "Emasculator" after believing it to castrate mammal hosts. No evidence has been found to verify permanent damage to scrotal area. Experiments involving White-Footed mice have been observed to swell, and become temporarily infertile.[7] The larvae of some species grow in the flesh of their hosts, while others grow within the hosts' alimentary tracts. This is due to the relation of the Gasterophilus intestinalis family, lay eggs in the nearest areas they detect warmth of areas licked by host. The larvae are then swallowed and grow in the stomach lining. Once the larvae have matured they then leave detach themselves and travel throughout the remaining intestines until it leaves the host's body with its fecal waste.[8]

The word "bot" in this sense means a maggot.[6] A warble is a skin lump or callus such as might be caused by an ill-fitting harness, or by the presence of a warble fly maggot under the skin. The human botfly, Dermatobia hominis, is the only species of bot flies whose larvae ordinarily parasitise humans, though flies in some other families episodically cause human myiasis, and are sometimes more harmful. In the United States alone 30 kinds of the Botfly species have been found. To name a few are the Mouse Bot Fly, Horse Botfly, and the Human Botfly. [9]

The "bot" fly will hijack a mosquito to inject the host with the eggs. It latches onto several species which allow the larvae to enter the skin of the host. The warble larvae has spikes on it that causes slight pain and redness while living on the skin of the host. The larvae generally does not affect the overall health of its live host.[10]

Family Oestridae[edit]

The Oestridae now are generally defined as including the former families Oestridae, Cuterebridae, Gasterophilidae, and Helodermatidae as subfamilies.

The Oestridae, in turn, are a family within the superfamily Oestroidea, together with the families Calliphoridae, Rhinophoridae, Sarcophagidae, and Tachinidae.

Of families of flies causing myiasis, the Oestridae include the highest proportion of species whose larvae live as obligate parasites within the bodies of mammals. Roughly 150 species are known worldwide.[11] Most other species of flies implicated in myiasis are members of related families, such as blowflies and screwworm flies in the Calliphoridae.


Larval stage of Gasterophilus intestinalis

Botflies deposit eggs on a host, or sometimes use an intermediate vector such as the common housefly, mosquitoes, and, in the case of Dermatobia hominis, a species of tick. They are common in Belize. The smaller fly is firmly held by the botfly female and rotated to a position where the botfly attaches some 30 eggs to the body under the wings. Larvae from these eggs, stimulated by the warmth and proximity of a large mammal host, drop onto its skin and burrow underneath.[12] Intermediate vectors are often used since a number of animal hosts recognise the approach of a botfly and flee.[13] In the United States botfly season starts in March in the South, and in June for North. The adult fly has no mouth, and its purpose is to begin the cycle by laying eggs on potential hosts before Winter. It only lives up to a few day or weeks depending on location.[14]

Eggs are deposited on animal skin directly, or the larvae hatch and drop from the eggs attached to the intermediate vector: the body heat of the host animal induces hatching upon contact or immediate proximity. Some forms of botfly also occur in the digestive tract after ingestion by licking.

Ox warble fly (Hypoderma bovis)

Myiasis can be caused by larvae burrowing into the skin (or tissue lining) of the host animal. Mature larvae drop from the host and complete the pupal stage in soil. They don't kill the host animal, thus are true parasites. Myiasis also affects pets, such as dog and cats. The infestation occurs after flys lay eggs onto opened broken skin, such as wounds. Untreated wounds lead to lesions of several formations from hatched larvae that consume the remaining skin tissue. The eyes, noses, wounds, and anus of live animals allow larvae to enter and create lesions. [15]


Hosts that have been targeted by the Botfly such as Rabbits are safe and healthy enough to be consumed.[16] Chipmunks, and tree squirrels are common hosts in the Eastern part of the North America region.[17]Horses often can detect when botflies approach them, which then causes them to fight with the flying insect. Other potential hosts range of variety of all mammals. Caribous, camels, elephants to small house pets are known to become hosts.[18] Birds have also been found to have the larvae of Botflies living in their skins as well.[19]

The equine botfly presents seasonal difficulties to equestrian caretakers, as it lays eggs on the insides of horses' front legs, on the cannon bone and knees, and sometimes on the throat or nose, depending on the species. These eggs, which look like small, yellow drops of paint, must be carefully removed during the laying season (late summer and early fall) to prevent infestation in the horse. When a horse rubs its nose on its legs, the eggs are transferred to the mouth, and from there to the intestines, where the larvae grow and attach themselves to the stomach lining or the small intestine. The attachment of the larvae to the tissue produces a mild irritation which results in erosions and ulcerations at this site.[20] Removal of the eggs (which adhere to the host's hair) is difficult, since the bone and tendons are directly under the skin on the cannon bones: eggs must be removed with a sharp knife (often a razor blade) or rough sand paper, or simply applying pressure with a glass bottle and caught before they reach the ground. The larvae remain attached and develop for 10–12 months before they are passed out in the feces. Occasionally, horse owners report seeing the botfly larvae in horse manure. These larvae are cylindrical in shape and are reddish orange in color. In one to two months, adult botflies emerge from the developing larvae and the cycle repeats.[20] Bots can be controlled with several types of dewormers, including dichlorvos, ivermectin, and trichlorfon. Though there are several deworming medication varied by forms, flavors, and class. Ivermectin, being the most effective and safest to use on breeds of all ages. This dosage for this medication is based on the weight and can be given to pregnant horses. Owners can safely give a 1,200 pound horse a full dose and be free of overdosing. This deworming medication is a pase like substance that can be squeezed and poured directly into the side of the horse' mouth. One common error is the use of Pyrantel, this is not effective to remove botflies. The liquid form is best used as a daily deworming method if eggs of other parasites are observed. Though it is best to consult with a vet to create a stable deworming schedule every 8 weeks based weather, for winters can spare two weeks.[21]

In cattle, the lesions caused by these flies can become infected by Mannheimia granulomatis, a bacterium that causes lechiguana, characterized by rapid-growing, hard lumps beneath the skin of the animal. Without antibiotics, an affected animal will die within three to 11 months.[22][23]


The human botfly occasionally uses humans to host its larvae. The larva, because of its spines, can pose an extremely painful subepidermal condition. The fastest way to remove a botfly is by putting a generous amount of iodine in the hole. The botfly will react instantly by poking out of the hole. After nearly six weeks of living in a human it will pupate into the soil[24]. Another removal method is to use the tree sap of the matatorsalo, found in Costa Rica, which is reputed to kill the larva, yet leave its body in the skin.[25] Additionally, one can attempt to seal the breathing hole of the larva with nail polish or petroleum jelly; after a day, with a clinical professional, the breathing hole is enlarged and the larva is removed with forceps. Squeezing the larvae out is not recommended, as it can cause the larvae to rupture; their bodily fluids have been known to cause severe anaphylactic shock.[26] Use of adhesive tape can work, but carries additional risk of infection because portions of the larva's breathing tube can be broken off by the tape and make the remainder of the body difficult to remove. A method that has been observed on Youtube is to sanitize the warbles breathing hole and to firmly squeeze down around the area with tweezers. The botfly larvae is covered in tiny back sharp hooks to prevent it from falling out. The pressure will then cause the larvae to begin to push itself out for fast extraction. A clean set of tweezers can be used to gently remove the larvae from the hooks. The host will often be left with a hole that will fully heal after a week.[27]

Dissected head of a deer showing botfly larvae

Consumption of maggots by humans[edit]

In cold climates supporting reindeer or caribou-reliant populations, large quantities of Hypoderma tarandi (caribou warble fly) maggots are available to human populations during the butchery of animals.[28]

The sixth episode of season one of the television series Beyond Survival entitled "The Inuit - Survivors of the Future" features survival expert Les Stroud and two Inuit guides hunting caribou on the northern coast of Baffin Island near Pond Inlet, Nunavut, Canada. Upon skinning and butchering of one of the animals, numerous larvae (presumably Hypoderma tarandi, although not explicitly stated) are apparent on the inside of the caribou pelt. Stroud and his two Inuit guides eat (albeit somewhat reluctantly) one larva each, with Stroud commenting that the larva "tastes like milk" and was historically commonly consumed by the Inuit people.[29]

Copious art dating back to the Pleistocene in Europe confirms their consumption in premodern times, as well.[30]

See also[edit]


  1. ^ Insects and Spiders of the World. Marshall Cavendish. 2003. ISBN 9780761473442. 
  2. ^ Loker, Eric; Hofkin, Bruce (2015-03-02). Parasitology: A Conceptual Approach. Garland Science. ISBN 9781317407720. 
  3. ^ Inc. Merriam-Webster (2011). Webster's American English dictionary. Springfield, MA: Federal Street Press. ISBN 978-1-59695-114-3. 
  4. ^ Mullen, Gary; Durden, Lance, eds. (2009). Medical and veterinary entomology. Amsterdam, NL: Academic. ISBN 978-0-12-372500-4. 
  5. ^ Journal of the Department of Agriculture of Western Australia, Volume 9, Pub: Western Australia. Dept. of Agriculture, 1904, p 17
  6. ^ a b Brown, Lesley (1993). The New shorter Oxford English dictionary on historical principles. Oxford [Eng.]: Clarendon. ISBN 0-19-861271-0. 
  7. ^ Timm, Robert M.; Lee, Richard E. (1981-07-31). "Do Bot Flies, Cuterebra (Diptera: Cuterebridae), Emasculate their Hosts?". Journal of Medical Entomology. 18 (4): 333–336. doi:10.1093/jmedent/18.4.333. ISSN 0022-2585. 
  8. ^ Cranshaw, Whitney; Redak, Richard (2013-09-15). Bugs Rule!: An Introduction to the World of Insects. Princeton University Press. ISBN 140084892X. 
  9. ^ "10 Disgusting Facts about the Bot Fly (The Day I Met a Cuterebra Larva)". Travel For Wildlife. 2017-09-22. Retrieved 2017-11-27. 
  10. ^ Staker, Lynda (2006). The Complete Guide to the Care of Macropods. Lynda Staker. ISBN 9780977575107. 
  11. ^ Pape, Thomas (April 2001). "Phylogeny of Oestridae (Insecta: Diptera)". Systematic Entomology. 26 (2): 133–171. doi:10.1046/j.1365-3113.2001.00143.x. 
  12. ^ Dunleavy, Stephen (producer) (2005-10-20). Life In The Undergrowth: Intimate Relations (Programme synopses). BBC. Retrieved 2008-12-17. 
  13. ^ Drees, B.M.; Jackman, John (1999). "Horse Bot Fly". Field Guide to Texas Insects. Houston, Texas: Gulf Publishing Company. Retrieved 12 June 2013. 
  14. ^ Gillespie, James R.; Flanders, Frank (2009-01-28). Modern Livestock & Poultry Production. Cengage Learning. ISBN 1428318089. 
  15. ^ Hnilica, Keith A. (2016-08). Small Animal Dermatology - E-Book: A Color Atlas and Therapeutic Guide. Elsevier Health Sciences. ISBN 9780323390675.  Check date values in: |date= (help)
  16. ^ "Human Botfly, Bot Fly, Botflies, Torsalo, Dermatobia hominis". Retrieved 2017-11-26. 
  17. ^ Jordan Taheri, Phillip Kaufman, and Frank Slansky2 (2007). Tree Squirrel Bot Fly, Cuterebra emasculator Fitch (Insecta: Diptera: Oestridae).  line feed character in |title= at position 51 (help)
  18. ^ Insects and Spiders of the World. Marshall Cavendish. 2003. ISBN 9780761473442. 
  19. ^ Forsyth, Adrian; Miyata, Ken (2011-05-24). Tropical Nature: Life and Death in the Rain Forests of Central and. Simon and Schuster. ISBN 9781439144749. 
  20. ^ a b Ondrak, Julie. "Ask The Vet: Treating Bot Infestations In Horses". Retrieved 2009-09-10. 
  21. ^ Madden, Markie (2014-09-01). Keeping a Backyard Horse. Metamorph Publishing. ISBN 9781501002328. 
  22. ^ Piper, Ross (2007). "Human Botfly". Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals. Westport, Connecticut: Greenwood Publishing Group. pp. 192–194. ISBN 0-313-33922-8. OCLC 191846476. Retrieved 2009-02-13. 
  23. ^ Riet-Correa, F.; S. L. Ladeira; G. B. Andrade; G. R. Carter (December 2000). "Lechiguana (focal proliferative fibrogranulomatous panniculitis) in cattle". Veterinary Research Communications. 24 (8): 557–572. doi:10.1023/A:1006444019819. PMID 11305747. 
  24. ^ "Human Botfly, Bot Fly, Botflies, Torsalo, Dermatobia hominis". Retrieved 2017-11-26. 
  25. ^ Pariser, Harry S (2006). Explore Costa Rica. Manatee Press. ISBN 1-893643-55-7. 
  26. ^ [1] Archived July 28, 2013, at the Wayback Machine.
  27. ^ "The Traveler's Medical Guide".  External link in |website= (help)
  28. ^ Felt, E.P. (1918). "Caribou warble grubs edible". Journal of Economic Entomology. 11: 482. 
  29. ^ "Les Stroud Beyond Survival: The Inuit - Survivors of the Future". Archived from the original on 2016-03-02. Retrieved 2015-11-10. 
  30. ^ Guthrie, Russell Dale (2005). The Nature of Paleolithic Art. University of Chicago Press. pp. 6–. ISBN 978-0-226-31126-5. Retrieved 7 May 2013. 

External links[edit]

On the UF / IFAS Featured Creatures Web site