Bot flies are insects whose larval stages develop as internal parasites within mammals. These flies belong to the family Oestridae and are characterized by their segmented, grub-like larvae. Adult bot flies typically have a stout, bee-like appearance but are rarely observed. Unlike many other insects, adult bot flies do not feed, as their mouthparts are reduced or absent. Their primary purpose as adults is reproduction.
Presence in Florida
Bot flies are present in Florida, primarily through various species that parasitize animals. While the human bot fly (Dermatobia hominis), commonly associated with human infestations in tropical regions, is not native to Florida, other species are found throughout the state. Cases of human bot fly infestation in Florida typically involve individuals who have traveled to endemic areas in Central or South America and returned with the larvae. Cuterebra species are active in Florida for much of the year, especially from late spring to early winter, with peak populations in late summer.
Common Species
Several bot fly species are common in Florida, each with specific animal hosts. Cuterebra species, often called rodent or rabbit bot flies, are prevalent throughout North America, including Florida. These flies typically lay eggs near the burrows or runways of their preferred hosts, such as rodents and rabbits. Once hatched, the larvae crawl onto the host or enter through natural openings like the nose, mouth, or small skin abrasions, eventually developing under the skin.
Cattle grubs (Hypoderma lineatum and Hypoderma bovis) primarily affect cattle. Horse bot flies (Gasterophilus intestinalis) are also widespread and parasitize horses. Female horse bot flies lay their eggs on the horse’s hair, often on the forelegs. The larvae then enter the horse’s mouth during grooming, eventually migrating to the digestive tract.
Signs of Infestation
Signs of bot fly infestation vary depending on the host and species, but a common indicator is the presence of a “warble.” This boil-like swelling forms under the skin, with a small central hole. This opening, a breathing hole, allows the bot fly larva to access air.
In animals like squirrels, dogs, or rabbits, the warble is often visible as a noticeable lump, sometimes with a yellowish or bloody discharge. Dogs might show discomfort, excessive licking, or scratching at the affected area. For humans, an infestation typically presents as a slowly enlarging nodule that may itch or cause a sensation of movement beneath the skin. While generally not life-threatening, the lesion can be painful, and secondary bacterial infections are possible if the site is not kept clean.
Prevention and Care
Preventing bot fly infestations involves minimizing exposure to environments where the flies lay eggs. For pets and livestock, this means avoiding areas frequented by rodents and rabbits, such as burrows or wooded spaces, especially during peak bot fly season. Regularly checking animals for suspicious lumps or skin changes can help detect infestations early. Using veterinary-approved insect repellents can also deter adult flies from laying eggs.
If an infestation is suspected, seeking professional veterinary or medical attention is important. Attempting to remove bot fly larvae yourself is not recommended due to potential complications. Squeezing the larva can cause it to rupture, leading to severe inflammation, allergic reactions, or secondary infections from retained body parts. Professionals can safely extract the larva, often by surgical removal or by suffocating it with petroleum jelly to encourage emergence, followed by proper wound care to prevent infection.