botfly

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Botfly
Horse botfly (Gasterophilus intestinalis)
Scientific classification
Kingdom: Animalia Phylum: Arthropoda Class: Insecta Order: Diptera Section: Schizophora Subsection: Calyptratae Superfamily: Oestroidea Family: Oestridae
Subfamilies
Cephenemyiinae Cuterebrinae Gasterophilinae Hypodermatinae Oestrinae

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]

Only one bot fly species attacks humans, the Dermatobia hominis.

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 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; if the lump happens to be where the saddle or bridle go, the horse is rendered unrideable 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.

In cattle, the lesions caused by these flies can become infected by a bacteria 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.^[3][4]

Botflies can, on occasion, lay their eggs on humans. The larva, because of their spines, then 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.^[5][6]

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
• Bolivia
• Chile
• Southern United States
• Mexico
• Honduras
• Panama
• Costa Rica
• Dominican Republic
• The coast of Ecuador
• Peru
• Argentina
• Several small provinces in Africa.
• Southern Ontario in Canada
• Hungary
• Northern British Columbia, Canada
• and England - nameley Surrey
• Adelaide - Elizabeth, Davoren Park
• New Zealand

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.^[7]

References

External links

• Removing Bot Fly larve from an infected human
• Encyclopedia.com article
• "Bug Attack" documentary: includes footage and description of botflies
• A snopes article concerning a botfly infestation
• Human Botfly, Description and Cure

on the UF / IFAS Featured Creatures Web site

• Cuterebra emasculator, squirrel bot fly
• Dermatobia hominis, human bot fly
• Gasterophilus intestinalis, horse bot fly
• Hypoderma lineatum, common cattle grub

Wikimedia Commons has media related to: Oestridae