The term “flesh-eating flies” refers to insects whose larvae, known as maggots, infest live animals, including humans. This parasitic infestation is scientifically termed myiasis, where fly larvae feed on a host’s tissue, bodily fluids, or ingested food. While the term “flesh-eating” covers various feeding strategies, myiasis can range from benign superficial infestations to severe tissue damage.
Types of Flies and Their Methods
The New World screwworm (Cochliomyia hominivorax) is an obligate parasite, meaning its larvae require living tissue for development. Female screwworms lay hundreds of eggs in open wounds. Once hatched, the larvae aggressively burrow into the flesh, tearing at living tissue and enlarging the wound as they feed. This burrowing action gives them their “screwworm” name.
The human botfly (Dermatobia hominis) uses a unique infestation method. The female botfly attaches her eggs to a blood-feeding arthropod, often a mosquito. When the mosquito lands on a warm-blooded host, body heat triggers the eggs to hatch, and larvae penetrate the skin. A single larva develops beneath the skin, forming a boil-like nodule with a central breathing pore. These larvae feed on tissue exudates and secretions, not actively consuming living flesh.
Other flies, like certain blow fly species (Calliphoridae), are opportunistic myiasis-producing flies. They are primarily attracted to decaying organic matter or necrotic tissue but can infest neglected wounds or soiled hair on living hosts. Their larvae feed on dead cells, exudates, and debris within the wound. While they can irritate and injure surrounding skin, they do not consume healthy living tissue like obligate parasites.
Geographic Distribution and At-Risk Populations
Myiasis-causing flies are largely confined to tropical and subtropical regions. The New World screwworm (Cochliomyia hominivorax) is endemic in South America and parts of the Caribbean, including Cuba, Haiti, and the Dominican Republic. Though eradicated from the United States and continental Central America, occasional re-emergences can occur.
The human botfly (Dermatobia hominis) is indigenous to tropical Central and South America, from southern Mexico to northern Argentina, excluding Chile. Travelers in rural areas within these regions are at heightened risk, especially if outdoors or with open wounds. Livestock and pets with unattended injuries are also highly susceptible to infestation by screwworms and opportunistic flies.
Signs of Infestation and Medical Response
Recognizing myiasis signs is important for prompt medical attention. For human botfly infestations, a common symptom is a growing, painful, firm lump under the skin, resembling a boil. This lesion often has a small, central opening, which is the larva’s breathing hole. Patients may report itching, shooting pain, or feel the larva’s movement, especially when showering or applying pressure.
New World screwworm infestation symptoms include an enlarging, painful wound that may bleed and emit a foul odor. The larvae, resembling a wood screw, may be visible within or around the wound, and individuals might feel their movement as they burrow deeper. Wounds can become severely damaged, and secondary bacterial infections are common, potentially leading to fever or chills.
Medical response for myiasis involves professional removal of the larvae. Self-treatment, such as squeezing or rupturing the larva, is discouraged due to risks of severe infection, allergic reactions, or leaving embedded fragments. Healthcare providers use techniques like surgical extraction or methods that encourage the larva to emerge by occluding its breathing hole, allowing for easier removal.
Prevention and Protection
Proactive measures prevent myiasis, especially for travelers to endemic regions. Wear long-sleeved shirts and long pants as a physical barrier against biting insects, and apply DEET-containing insect repellents to exposed skin. Be cautious when drying clothes outdoors, as some flies lay eggs on damp laundry; ironing clothes, especially underwear and socks, can kill deposited eggs.
For pet and livestock owners, diligent wound care and regular animal inspection are important. Promptly cleaning and treating open wounds deters flies from laying eggs, as many myiasis-causing flies are attracted to fresh injuries. Maintaining good hygiene and clean animal living areas also reduces the presence of flies that cause opportunistic infestations.