Flesh flies, known for their scavenging habits, are a common subject of public curiosity, particularly concerning their reproductive interactions with humans. Understanding their biology and typical behaviors helps clarify this common concern.
The Flesh Fly Defined
Flesh flies belong to the family Sarcophagidae, a large group of flies found worldwide. They are generally medium to large in size, typically ranging from 4.1 to 22.9 millimeters (0.16 to 0.9 inches) in length. A distinctive feature of many flesh flies is their gray body with three prominent black stripes running lengthwise on the thorax, the section behind the head. Their abdomen often displays a checkered pattern of light and dark gray, and some species may have a reddish or orange tip. These flies also possess noticeable red eyes and a bristly appearance.
Where Flesh Flies Typically Deposit Larvae
Flesh flies are viviparous, meaning they deposit live larvae, also known as maggots, rather than eggs. Unlike many other fly species, flesh fly eggs hatch inside the female’s body. The female then selects a suitable substrate to deposit these live young. Their preferred natural breeding sites are decaying organic matter, such as carrion (dead animals), animal feces, or rotting vegetation. Larvae immediately begin feeding on this organic material.
Flesh Flies and Human Interaction
Flesh flies do not typically deposit larvae on healthy human tissue. Their attraction to humans is opportunistic, occurring when they encounter open wounds, necrotic (dead) tissue, or soiled skin. This unintentional infestation by fly larvae is known as myiasis. While rare in healthy individuals, accidental myiasis can occur, particularly in people with poor hygiene, pre-existing conditions, or those who are immobile.
Larvae might be deposited in an existing wound, where they feed on the decaying flesh. Flesh flies prefer decomposing organic matter as their food source, so human infestations are not a primary target. However, untreated wounds or unhygienic conditions can attract female flesh flies seeking a suitable site for their larvae. In some reported cases, accidental intestinal myiasis can occur if larvae are ingested through contaminated food or water. This highlights the importance of proper sanitation to mitigate the risk of such occurrences.
Distinguishing Myiasis-Causing Flies
While flesh flies can cause myiasis, it is important to distinguish them from other fly species more commonly associated with human infestations or different methods of initiating them. Some, like the human botfly (Dermatobia hominis) or tumbu fly (Cordylobia anthropophaga), actively seek out living hosts. For example, the human botfly lays its eggs on other arthropods, like mosquitoes, which then transfer the larvae to a human host during a bite, burrowing under the skin. Screwworm flies (Cochliomyia hominivorax and Chrysomya bezziana) are also significant myiasis-causing flies that lay eggs directly near open wounds on animals and occasionally humans, with larvae capable of invading healthy tissue.
Unlike these species, most flesh flies are primarily scavengers attracted to decomposing material. Their involvement in human myiasis is largely a secondary event, typically occurring in the presence of existing wounds or compromised tissue rather than through direct, active parasitism of healthy skin.