Many people wonder if flies can lay eggs on humans. While most flies are simply a nuisance, certain species possess the ability to lay eggs on or near human bodies, leading to a parasitic condition. Understanding this phenomenon involves identifying the specific types of flies involved and how infestations occur.
The Reality of Fly Egg Laying on Humans
Some fly species are indeed capable of laying eggs on or near human tissue, resulting in a condition known as myiasis. Myiasis is a parasitic infestation where fly larvae, commonly called maggots, develop within the living tissue of a host, including humans. This behavior is limited to specific fly types that require a living host for larval development.
Myiasis is uncommon in the United States but more frequent in tropical regions. Myiasis cannot spread from one human to another; flies, ticks, and mosquitoes are the vectors.
Pathways to Infestation
Flies infest human skin through various methods, including direct contact and indirect transfer. One pathway is direct deposition, where certain fly species lay eggs directly onto human skin, especially on open wounds or broken skin. Flies are attracted to the odors and secretions from wounds, making these areas susceptible to egg-laying.
Another mechanism is indirect transfer. Some flies lay eggs on other insects, like mosquitoes or ticks, which then transfer the eggs to a human during a bite. Body warmth can cause these eggs to hatch, allowing larvae to penetrate the skin.
Identifying the Culprits and Their Impact
Several fly species cause myiasis in humans, each with distinct geographical distributions and effects. The human botfly, Dermatobia hominis, is common in Central and South America. This fly lays eggs on other insects, like mosquitoes, which transfer them to human skin during a bite. Once larvae burrow under the skin, they cause a painful, boil-like lesion with a central opening, often accompanied by a sensation of movement. The lesion may discharge fluid or blood.
The tumbu fly, Cordylobia anthropophaga, is found in tropical Africa. Female tumbu flies lay eggs on soil contaminated with feces or urine, or on damp clothing left to dry. Larvae hatch and can penetrate unbroken skin, causing furuncular myiasis, which appears as a red bump that enlarges into a boil-like sore. The affected area can become itchy and painful as the larva develops.
Screwworm flies, particularly the New World screwworm (Cochliomyia hominivorax), are found in South America and the Caribbean. These flies are attracted to open wounds and lay eggs directly on them. Larvae feed aggressively on living tissue, causing severe pain and tissue destruction.
Preventing and Addressing Infestations
Preventing myiasis involves minimizing exposure to myiasis-causing flies, especially in endemic regions. Wearing protective clothing, such as long-sleeved shirts and pants, can reduce exposed skin. Using insect repellents on skin and treating clothing with permethrin-containing products can deter flies. Promptly cleaning and covering any open wounds is important, as flies are attracted to these sites. In areas where tumbu flies are common, dry laundry indoors or iron clothes after drying them outdoors, as heat can destroy any eggs.
If an infestation is suspected, seek medical attention for proper diagnosis and larval removal. Healthcare providers can identify the myiasis type and determine the appropriate course of action. While some methods exist to encourage larvae to emerge, such as occluding the breathing hole with petroleum jelly, medical removal is often required. Surgical removal of larvae is a common and effective treatment, and anti-parasitic medications like ivermectin may be prescribed. Attempting self-treatment can be risky and may lead to complications or incomplete removal.