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From Wikipedia, the free encyclopedia

Horse botfly (Gasterophilus intestinalis)
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Diptera
Section: Schizophora
Subsection: Calyptratae
Superfamily: Oestroidea
Family: Oestridae
Larval stage of Gasterophilus intestinalis
Ox warble-fly (Hypoderma bovis)
Dissected head of a deer showing bot fly larvae

The botfly is a family of Oestroidea. It is one of several families of hairy flies whose larvae live as parasites within the bodies of mammals. There are approximately 150 known species worldwide.[1]

Dermatobia hominis, or human botfly, is the only species of botfly known to use humans as the host to its larvae.



Botflies deposit eggs in a host body, or sometimes use an intermediate vector: common houseflies for example. 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 of a large mammal host, drop onto its skin and burrow underneath.[2]

Eggs are deposited in animal skin directly, or the larvae drop from the egg: the body heat of the animal induces hatching upon contact. Some forms of botfly also reside in the digestive tract when consumed by a licking action.

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, and thus are true parasites (though some species of rodent-infesting botflies do consume the host's testes/ovaries).

The equine bot fly presents annual difficulties to equestrian caretakers, as it lays eggs on the insides of horse's front legs, on the cannon bone and knees, and sometimes on the throat or nose, depending on what type of bot fly does the laying. 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 stomachs lining or they pass into the small intestine and attach there. The attachment of the larvae to the tissue produces a mild irritation which results in erosions and ulcerations at this site.[3] 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, and caught before they reach the ground. The larvae remain attached and develop for 10–12 months before they are passed out of the body with the horse’s manure. Occasionally horse owners will report seeing the bot fly larvae in their horse’s manure. These larvae are cylindrical in shape and are reddish orange in color. In 1–2 months adult bot flies will emerge from the developing larvae and the cycle will repeat[3]. Bots 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.[4][5]

Certain type of Botflies can occasionally use humans as the host to its larvae. The larva, because of their spines, can pose an extremely painful sub-epidermal condition. Removal processes include placing raw meat on to the area, which in theory will coax the larva out. Another option is to use the tree sap of the matatorsalo, found in Costa Rica, which will kill the larva, yet leave its body in the skin. Additionally, one can attempt to seal the breathing hole of the larva with nail polish, vaseline or adhesive tape and then, after a day, squeeze out the suffocated, dead larva.[6][7]


Botflies live in a variety of places, mostly warm and damp climates including throughout Brazil and Chile. Countries with known botfly encounters:

Uses by humans

In cold climates supporting reindeer or caribou-reliant populations, large quantities of Oedomagena tarandi (warble fly) maggots are available to human populations during the butchery of animals. These are relished in modern times by some as important seasonal luxuries containing high levels of protein, fats and salt.

Copious art dating back to the Pleistocene in Europe confirms their importance in premodern times as well.[8]


  1. ^ Pape, Thomas (April 2001). "Phylogeny of Oestridae (Insecta: Diptera)". Systematic Entomology 26 (2): 133–171. doi:10.1046/j.1365-3113.2001.00143.x. 
  2. ^ Dunleavy, Stephen (producer). (2005-10-20). Life In The Undergrowth: Intimate Relations (Programme synopses). BBC. Retrieved 2008-12-17. 
  3. ^ a b Ondrak, Julie. "Ask The Vet: Treating Bot Infestations In Horses". Retrieved 2009-09-10. 
  4. ^ 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. 
  5. ^ Riet-Correa, F.; S. L. Ladeira, G. B. Andrade and 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. 
  6. ^
  7. ^ Pariser, Harry S (2006). Explore Costa Rica. Manatee Press. ISBN 1-893643-55-7. 
  8. ^ Guthrie, Russell Dale (2005). The Nature of Paleolithic Art. Chicago: University of Chicago Press. p. 6. ISBN 0-226-31126-0. 

External links

On the UF / IFAS Featured Creatures Web site

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