Blow flies (bottle flies) are common insects belonging to the family Calliphoridae. They are often recognized by their metallic blue, green, or bronze sheen and are frequently seen around homes and businesses worldwide. Blow flies are considered “filth flies” due to their close association with unsanitary materials. This association often raises public concern regarding their interaction with humans, particularly the question of whether they can inflict a bite.
The Simple Answer: Understanding Blow Fly Mouthparts
The definitive answer is that blow flies do not possess the mouthparts necessary to bite or pierce human skin. Unlike mosquitoes or stable flies, which use sharp, needle-like stylets for piercing, the adult blow fly has a sponging-lapping feeding apparatus. Their mouthparts are specialized only for ingesting liquid food.
The most visible part of this apparatus is the proboscis, which ends in two fleshy pads called the labella. The surface of the labella is covered with minute channels called pseudotracheae, which function like tiny sponges. When feeding, the fly secretes saliva onto a solid food source to dissolve it, creating a liquid solution. This liquid is then drawn up into the mouth via capillary action. This mechanism is effective for consuming liquids or liquefied solids but is completely incapable of breaking through skin.
What Attracts Blow Flies to Human Environments
Blow flies are primarily scavengers and decomposers, and their presence is directly linked to the availability of decaying organic matter. Their acute sense of smell allows them to detect the odors of decomposition, such as putrescine and cadaverine, from great distances. They are often the first insects to arrive at carrion, sometimes within minutes of an animal’s death, which is why they are important in forensic science.
In human environments, their attraction is centered on materials necessary for their reproductive cycle, which involves laying eggs. Female blow flies typically deposit their eggs on dead animals, rotting meat, uncovered garbage, and animal feces. The resulting larvae, or maggots, feed on this decaying material to grow. Poorly managed compost piles, unsealed trash receptacles, and pet waste are strong attractants that sustain local blow fly populations.
Health Concerns Associated with Blow Flies
Since blow flies do not bite, the primary health risk they pose is their ability to act as mechanical vectors for pathogens. By landing on contaminated sources like feces, carrion, and garbage, they pick up bacteria, viruses, and parasites on their bodies, legs, and mouthparts. They can then transfer these contaminants when they land on human food, kitchen surfaces, or open wounds.
This contact-based transmission can spread organisms like E. coli, Salmonella species, and Helicobacter pylori, which are associated with gastrointestinal illness and other infections. A more specific, though rarer, health concern is myiasis, a parasitic infestation where fly larvae develop within the living tissue or body cavities of a host. Certain species of blow flies will lay their eggs in open wounds on animals and occasionally humans, where the hatched maggots begin to feed on the host’s tissue, requiring medical intervention.