The common house fly (Musca domestica) does not bite humans, a frequent misconception. These insects lack the mouthparts to pierce skin and draw blood, unlike other fly species often mistaken for them.
The Truth About House Flies
The common house fly (Musca domestica) does not bite because its mouthparts are not designed for piercing skin. Instead, house flies have sponge-like mouthparts adapted for lapping up liquids. When encountering solid food, a house fly secretes saliva to dissolve it, then sponges up the resulting solution. This feeding method means house flies consume only liquid or dissolved food, such as decaying organic matter or sugary substances.
Flies That Bite
While house flies do not bite, several other fly species possess specialized mouthparts to pierce skin and feed on blood. These biting flies are often the true source of painful “fly bites” experienced by humans and animals. For instance, stable flies (Stomoxys calcitrans), also known as biting house flies, are similar in size to common house flies but have a distinct, bayonet-like proboscis used for piercing and sucking blood. Both male and female stable flies feed on blood for reproduction.
Horse flies (Tabanus spp.) and deer flies (Chrysops spp.) are larger, robust flies with powerful, blade-like mouthparts. Females cut into the skin, creating an open wound to lap up pooling blood, and inject an anticoagulant. These females require a blood meal for egg production, and their bites are notably painful. Mosquitoes (Culicidae) are another common biting insect; only females bite for egg development. They use a long, needle-like proboscis to pierce skin and draw blood, a more precise method than the cutting action of horse or deer flies.
Why House Flies Are Still a Problem
Despite not biting, house flies are significant pests due to their role in disease transmission. They frequently land on unsanitary materials like decaying matter, feces, and garbage, picking up bacteria, viruses, and parasites on their bodies. When a house fly lands on food, food preparation surfaces, or utensils, these pathogens can be transferred.
House flies can mechanically transmit over 65 diseases to humans, including E. coli, Salmonella, cholera, and typhoid fever. They also spread pathogens by regurgitating digestive fluids or defecating on surfaces and food. Maintaining good hygiene and properly storing food mitigates these health risks.