Bot flies are parasitic insects whose larvae develop inside mammals. They are found in Colorado, with several species adapted to local wildlife.
Bot Fly Species in Colorado
Colorado is home to various bot fly species, each typically targeting specific animal hosts. Rodent and rabbit bot flies (Cuterebra genus) are common, infesting small mammals like deer mice, rabbits, squirrels, and other rodents.
Additionally, bot flies in the Cephenemyia genus are native to Colorado, specifically parasitizing deer and elk. Historically, domestic animal bot flies like the sheep bot fly (Oestrus ovis), horse bot flies (Gasterophilus intestinalis, G. nasalis), and cattle grubs (Hypoderma bovis, H. lineatum) were reported. However, widespread anti-parasitic treatments in livestock have made these introduced species very rare.
The human bot fly (Dermatobia hominis) is prevalent in tropical Central and South America. Its presence in the United States, including Colorado, is extremely uncommon and typically involves accidental cases.
Understanding Bot Fly Infestation
The life cycle of a bot fly involves several stages: egg, larva (maggot), pupa, and adult fly. Adult female bot flies do not feed, focusing solely on reproduction during their short lifespan of about two weeks.
Infestation typically begins when an adult female lays eggs near the entrance of a host animal’s burrow, on vegetation, or directly on the host’s fur. The warmth of a passing host can trigger the eggs to hatch, and the tiny larvae then enter the animal through natural openings like the nose or mouth, or occasionally through skin abrasions.
Once inside, the larvae migrate through the host’s tissues, eventually settling under the skin where they create a distinct swelling called a warble. This warble features a small breathing hole, allowing the larva to access air as it develops. Larval development can take several weeks to a few months, after which the mature larva exits the host and burrows into the soil to pupate.
While bot fly larvae rarely cause death in their primary animal hosts, their presence can lead to discomfort, secondary bacterial infections, or, in rare instances, more severe complications if they migrate to critical areas like the brain or eyes. Human infestations usually occur incidentally, often from contact with infested animals or environments.
Protecting Against Bot Flies
Preventative measures can reduce the risk of bot fly infestations, especially for pets and livestock. For domestic animals, keep them indoors or limit access to areas with high rodent and rabbit activity, particularly during summer and early fall. Regular grooming and inspecting fur for unusual lumps can aid early detection. Consulting a veterinarian about animal-approved insect repellents may also offer protection.
If a bot fly infestation is suspected in an animal, seeking veterinary care is recommended. Veterinarians can safely remove the larva, often through manual extraction, and treat the wound to prevent secondary infections. Attempting to remove the larva at home is not advised, as it can cause the larva to rupture, leading to severe inflammation or infection.
For livestock, effective pasture management and consistent deworming programs, often including medications like ivermectin, are important for controlling bot fly populations. For humans, wearing protective clothing and using insect repellent when in wooded or brushy areas can help minimize accidental exposure.