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Deer botfly Cephenemyia stimulator
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Diptera
(unranked): Eremoneura
(unranked): Cyclorrhapha
Section: Schizophora
Subsection: Calyptratae
Superfamily: Oestroidea
Family: Oestridae
Leach, 1815
Juvenile male Ecuadorian mantled howler (Alouatta palliata aequatorialis) with botfly parasites

Botflies, also known as warble flies, heel flies, and gadflies, are a family of flies known as the Oestridae. Their larvae are internal parasites of mammals, some species growing in the host's flesh and others within the gut. Dermatobia hominis is the only species of botfly known to parasitize humans routinely, though other species of flies cause myiasis in humans.


A botfly,[1] also written bot fly,[2] bott fly[3] or bot-fly[4] 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. The larvae of some species grow in the flesh of their hosts, while others grow within the hosts' alimentary tracts.

The word "bot" in this sense means a maggot.[4] 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 botfly whose larvae ordinarily parasitise humans, though flies in some other families episodically cause human myiasis and are sometimes more harmful.

Family Oestridae[edit]

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

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

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.[5] Most other species of flies implicated in myiasis are members of related families, such as blow-flies.


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 D. hominis, a species of tick. After mating, the female botfly captures the phoretic insect by holding onto its wings with her legs. She then makes the slip—attaching 15 to 30 eggs onto the insect or arachnid's abdomen, where they incubate. The fertilized female does this over and over again to distribute the 100 to 400 eggs she produces in her short adult stage of life of only 8–9 days. Larvae from these eggs, stimulated by the warmth and proximity of a large mammal host, drop onto its skin and burrow underneath.[6] Intermediate vectors are often used, since a number of animal hosts recognize the approach of a botfly and flee.[7]

Eggs are deposited on larger animals' 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 do not kill the host animal, thus they are true parasites.

The equine botflies present seasonal difficulties to equestrian caretakers, as they lay eggs on the insides of horses' front legs on the cannon or metacarpal bone (below the knee) 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 the site.[8] 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 sandpaper 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 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 itself.[8] Botflies can be controlled with several types of dewormers, including dichlorvos, ivermectin, and trichlorfon.

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 3–11 months.[9][10]

Philornis botflies often infest nestlings of wild parrots, like scarlet macaws[11] and hyacinth macaws.[12] A method using a reverse syringe design snake bite extractor proved to be suitable for removing larvae from the skin.[11]

Cuterebra fontinella, the mouse botfly, parasitizes small mammals all around North America.[13]

Dermatobia hominis, the human botfly, occasionally uses humans to host its larvae.[14]

As human food[edit]

Dissected head of a deer showing botfly larvae

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.[15]

The sixth episode of season one of the television series Beyond Survival, titled "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 H. 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.[16]

Copious art dating back to the Pleistocene in Europe confirms their consumption in premodern times, as well.[17]

The Babylonian Talmud Hullin 67b discusses whether the warble fly is kosher.[18]

See also[edit]


  1. ^ Inc. Merriam-Webster (2011). Webster's American English dictionary. Springfield, MA: Federal Street Press. ISBN 978-1-59695-114-3.
  2. ^ Mullen G, Durden L, eds. (2009). Medical and veterinary entomology. Amsterdam, NL: Academic. ISBN 978-0-12-372500-4.
  3. ^ Journal of the Department of Agriculture of Western Australia, Volume 9, Pub: Western Australia. Dept. of Agriculture, 1904, p 17
  4. ^ a b Brown, Lesley (1993). The New shorter Oxford English dictionary on historical principles. Oxford [Eng.]: Clarendon. ISBN 0-19-861271-0.
  5. ^ Pape T (April 2001). "Phylogeny of Oestridae (Insecta: Diptera)". Systematic Entomology. 26 (2): 133–171. Bibcode:2001SysEn..26..133P. doi:10.1046/j.1365-3113.2001.00143.x. S2CID 83936667.
  6. ^ Dunleavy, Stephen (producer) (2005-10-20). Life In The Undergrowth: Intimate Relations (Programme synopses). BBC. Retrieved 2008-12-17.
  7. ^ Drees B, Jackman J (1999). "Horse Bot Fly". Field Guide to Texas Insects. Houston, Texas: Gulf Publishing Company. Archived from the original on 2012-11-14. Retrieved 12 June 2013.
  8. ^ a b Ondrak J. "Ask The Vet: Treating Bot Infestations In Horses". Archived from the original on 2009-08-22. Retrieved 2009-09-10.
  9. ^ Piper R (2007). "Human Botfly". Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals. Westport, Connecticut: Greenwood Publishing Group. pp. 192–194. ISBN 978-0-313-33922-6. OCLC 191846476. Retrieved 2009-02-13.
  10. ^ 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. S2CID 19888515.
  11. ^ a b Olah G, Vigo G, Ortiz L, Rozsa L, Brightsmith DJ (2013). "Philornis sp. bot fly larvae in free living scarlet macaw nestlings and a new technique for their extraction". Veterinary Parasitology. 196 (1–2): 245–249. doi:10.1016/j.vetpar.2012.12.052. PMID 23384580.
  12. ^ Allgayer MC, Guedes NM, Chiminazzo C, Cziulik M, Weimer TA (2009). "Clinical pathology and parasitologic evaluation of free-living nestlings of the Hyacinth Macaw (Anodorhynchus hyacinthinus)". Journal of Wildlife Diseases. 45 (4): 972–981. doi:10.7589/0090-3558-45.4.972. ISSN 0090-3558. PMID 19901373. S2CID 22897475.
  13. ^ Jennison CA, Rodas LR, Barrett GW (2006). "Cuterebra fontinella parasitism on Peromyscus leucopus and Ochrotomys nuttalli". Southeastern Naturalist. 5 (1): 157–168. doi:10.1656/1528-7092(2006)5[157:CFPOPL]2.0.CO;2. S2CID 87286185.
  14. ^ "Human Bot Fly Myiasis" (PDF). U.S. Army Public Health Command (provisional), formerly U.S. Army Center for Health Promotion and Preventive Medicine. January 2010. Retrieved 2014-08-14.
  15. ^ Felt E (1918). "Caribou warble grubs edible". Journal of Economic Entomology. 11: 482.
  16. ^ "Les Stroud Beyond Survival: The Inuit – Survivors of the Future". Archived from the original on 2016-03-02. Retrieved 2015-11-10.
  17. ^ Guthrie RD (2005). The Nature of Paleolithic Art. University of Chicago Press. pp. 6–. ISBN 978-0-226-31126-5. Retrieved 7 May 2013.
  18. ^ "Chullin 67b:11". Retrieved 2021-01-02.

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