botfly, common name for several families of hairy flies whose larvae live as parasites within the bodies of mammals. The horse botfly secretes an irritating substance that is used to attach its eggs to the body hairs of a horse, mule, or donkey. When the animal licks off the irritant, the larvae are carried into the host's mouth and later migrate to the stomach. They attach themselves to the lining, where they feed until ready to pupate, and then drop to the ground with the feces. The larvae, which may cause serious damage to the digestive tract and weaken the animal, can be eliminated by a veterinarian. Sheep botflies lay their eggs in the nostrils of the host without alighting. The larvae work their way up into the head cavities causing fits of vertigo known as blind staggers; failure to eat because of irritability may result in death. Old World species of this family attack camels, elephants, horses, mules, donkeys, and deer. The warble flies, also called heel flies, or bomb flies, parasitize cattle and other animals. The larvae, called cattle grubs or cattle maggots, penetrate the skin of the host immediately after hatching; they migrate through the flesh, causing irritability, loss of weight, and decreased milk production, and then settle under the skin of the back, producing cysts, or warbles. Breathing holes made in the warbles by the larvae damage the hide. A species of human botfly found in Central and South America attaches its eggs to a bloodsucking mosquito that it captures and then releases. When the mosquito comes in contact with humans or other warm-blooded animals, the fly eggs hatch and the larvae fasten to the mammal's skin. The larvae bore into muscle tissue; infestation is called myiasis. For control methods, see bulletins of the U.S. Dept. of Agriculture. The botflies are classified in the phylum Arthropoda, class Insecta, order Diptera. Horse botflies are classified in the family Gasterophilidae; sheep botflies and warble flies are classified in the family Oestridae; the human botfly is classified in the family Cuterebridae. See insect.

Oestridae (also called botfly or "bumfly" bot fly) is a family of Oestroidea. It is one of several families of hairy flies whose larvae live as parasites within the bodies of mammals, such as the Desert Woodrat. There are approximately 150 known species worldwide.

Only one bot fly species attacks humans, the Dermatobia hominis. For many years the deer botfly was cited as the fastest flying insect in the Guinness Book of World Records, but the claim has been refuted and is no longer considered probable.

Life cycle

  • Botflies deposit eggs in a host body, or sometimes use an intermediate vector: common houseflies for example.
  • 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 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 larva grows and migrates to the skin. When ready to emerge, a thumbnail-sized lump will appear on the horse, which is not painful, but if the lump happens to be where the saddle or bridle go, the horse will be out of commission until the wound made by the young bot fly’s emergence heals. Additionally, migrating larva may cause mouth sores, ulcers in the stomach, and blockage of the pyloric valve which could lead to colic. Removal of the eggs (which adhere to the host’s hair) is tricky, 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. During this process the human can also become infected. Bots can be controlled with several types of dewormers, including dichlorvos, ivermectin, and trichlorfon


Botflies live in a variety of places, mostly warm and damp climates including throughout Brazil and Chile, as well as far north as the southern United States.

Countries with known botfly encounters:

  • Brazil
  • Belize
  • Chile
  • Southern United States
  • Mexico
  • Honduras
  • Panama
  • Costa Rica
  • Dominican Republic
  • Peru
  • Argentina
  • Several small provinces in Africa.
  • Southern Ontario in Canada
  • Hungary
  • Northern British Columbia, Canada


  • Pape, Thomas (2001). "Phylogeny of Oestridae (Insecta: Diptera)". Systematic Entomology 26 (2): 133–171.

External links

on the UF / IFAS Featured Creatures Web site

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