Botflies are parasitic insects whose larvae develop within mammal tissues. These flies belong to the family Oestridae, and their life cycles are linked to specific hosts. Adult botflies are short-lived and non-feeding, but their larvae are obligate internal parasites, requiring a living host for development. Botfly presence is dictated by host animal availability and distribution.
Geographic Range and Climate Zones
Botfly distribution is influenced by climate and host availability. The human botfly, Dermatobia hominis, is found in tropical and subtropical Central and South America, from southern Mexico to northern Argentina. This species thrives in humid, tropical climates with dense vegetation, like rainforests, and near bodies of water. Cuterebra species, known as rodent and rabbit botflies, are prevalent across North America, covering the continental United States, southern Canada, and northeastern Mexico. Adult Cuterebra fontinella require temperatures above 20 °C and sunlight for activity. These botflies are often found at forest edges, near rodent dens. Horse botflies (Gasterophilus spp.) exhibit a more widespread global distribution.
Host Animals and Associated Environments
Botfly species display host specificity, adapted to parasitize particular animals. The human botfly (Dermatobia hominis) infests various warm-blooded vertebrates, including humans, cattle, horses, dogs, and some birds. Infestations typically occur in humid, cool secondary forests and coffee-growing highlands of tropical America, often associated with high mosquito populations. Cuterebra species primarily target rodents and rabbits. Cats and dogs can become accidental hosts, acquiring larvae when hunting near rodent burrows or exploring areas where these botflies lay eggs. Horse botflies (Gasterophilus spp.) primarily parasitize horses, mules, and donkeys, found in agricultural settings like stables and pastures. Deer botflies (Cephenemyia spp.) are specific to deer and elk, with larvae developing in their nasal passages in dense populations.
How Botflies Find Their Hosts
Botflies employ diverse strategies for depositing eggs and ensuring larval transmission. The human botfly (Dermatobia hominis) uses intermediate vectors like mosquitoes, other flies, or ticks. A female D. hominis glues 10-50 eggs onto a blood-feeding insect. When the vector lands on a warm-blooded animal, host body heat hatches the eggs, allowing larvae to burrow into the skin, often through a bite wound or hair follicle. Other botfly species, like Cuterebra, lay eggs directly in the environment near host activity. These locations include around animal nests or burrows, or on vegetation. Sensing host warmth, eggs hatch, and the tiny larvae enter the host’s body through natural openings, wounds, or by ingestion during grooming. Horse botflies (Gasterophilus spp.) lay eggs onto equine fur; larvae are ingested when the host licks or bites. Deer botflies (Cephenemyia spp.) flick newly hatched larvae directly into deer or elk nostrils. Once inside the host, larvae migrate to specific tissues, where they feed and develop, often creating a visible lump or “warble” in the skin through which they breathe.