Botflies are the parasitic larval stage of flies belonging to the family Oestridae, an insect group that includes about 150 species. Adult flies are often hairy and bee-like but lack functional mouthparts, living only long enough to reproduce. Their larvae are obligate parasites, meaning they must live inside a mammalian host to develop, a condition known as myiasis. The geographic distribution is complex, shifting globally based on the species and momentarily based on the insect’s life stage.
Global Presence and Key Regions
The Oestridae family is present on every continent except Antarctica, though the density and type of botfly vary dramatically with climate. Distribution follows the presence of suitable host mammals and necessary environmental conditions. This results in distinct regional groups, such as the Cuterebrinae, primarily found in the New World (the Americas), and the Hypodermatinae, associated with the Old World (Eurasia and Africa). Widespread genera, like the horse botflies (Gasterophilus), inhabit both temperate and tropical zones where domestic livestock are present. Other groups, such as the nose botflies (Oestrinae), originated in Africa and spread alongside their host animals.
The Human Botfly Habitat
The human botfly (Dermatobia hominis) is endemic to the tropical and semi-tropical regions of the Americas. Its range extends from southeastern Mexico, throughout Central America, and south into countries like Argentina and Uruguay. This distribution is tied to high humidity and warm temperatures, allowing populations to thrive in low-elevation tropical forests and moist coffee-growing highlands. The insect uses a unique reproductive strategy: it captures smaller, blood-feeding arthropods, such as mosquitoes, and cements its eggs to their bodies. When this vector lands on a warm-blooded host, the eggs hatch from the heat, and the larvae burrow into the skin.
Botflies of Livestock and Wildlife
The majority of botflies parasitize domestic and wild animals, and their locations are tied directly to the host’s range. Cattle botflies (Hypoderma), or warble flies, are widespread across the Northern Hemisphere, historically found between the 25th and 60th latitudes across North America, Europe, Asia, and North Africa. These species thrive in temperate pasturelands and farm environments where their primary hosts, cattle and deer, graze. Horse botflies (Gasterophilus) are found globally wherever equids are kept.
In the New World, the Cuterebra genus targets native wildlife; for example, the mouse botfly (C. fontinella) inhabits the continental United States, southern Canada, and northern Mexico, residing near its rodent and rabbit hosts. The sheep botfly (Oestrus ovis) also has a broad, global distribution, flourishing in subtropical and tropical regions where sheep are commercially raised.
Location During the Life Cycle
The location of a botfly shifts completely through the four stages of its life cycle. The adult fly, which is non-feeding, exists briefly in the air near host populations solely to reproduce. Eggs are located either on a vector insect, on vegetation, or cemented directly to the hair of a host animal, such as a horse’s foreleg. The larval stage is the longest, occurring inside the host mammal.
Depending on the species, this internal location can be the subcutaneous tissue beneath the skin, the gastrointestinal tract (stomach or duodenum), or the nasopharyngeal cavities of the head. Once the larva matures, it exits the host and drops to the ground, undergoing the pupal stage in the soil until it emerges as a new adult fly.