Flies do not possess the anatomical structure required to sting, a mechanism exclusively used by other types of insects. Any painful sensation felt is the result of a bite. Flies that cause irritation or draw blood are equipped with specialized mouthparts to pierce the skin and feed. This feeding behavior is fundamentally different from the defensive venom injection employed by true stinging insects like bees and wasps. Understanding this difference clarifies why some flies inflict a noticeable wound while others, like the common house fly, are merely nuisances.
The Difference Between Stinging and Biting
The distinction between a bite and a sting rests entirely on the insect’s anatomy and the biological purpose of the action. A true sting is delivered by a modified ovipositor, found in insects like bees, wasps, and hornets. This organ has evolved into a venom-injecting apparatus used primarily for defense or subduing prey. The reaction to a sting is caused by the injection of venom.
Biting, conversely, is an action performed with an insect’s mouthparts. Biting flies use various structures, such as a sharp proboscis or scissor-like mandibles, to penetrate the host’s skin and access blood or other fluids. They inject saliva containing anti-coagulants and sometimes anesthetics to facilitate feeding, and the subsequent irritation, pain, and swelling are reactions to these salivary components.
Common Types of Biting Flies
The stable fly, which closely resembles the common house fly, is a blood feeder that uses a pointed, rigid proboscis to stab the skin. Both male and female stable flies feed on blood, typically targeting the ankles or lower legs, and their bite causes a sharp, stabbing sensation. They are most active in late summer and early fall, often near livestock or decaying vegetation where they breed.
Horse flies and deer flies inflict a particularly painful bite due to their feeding mechanism. These flies use scissor-like mouthparts to slash and tear the skin, creating an open wound from which they then lap up the pooling blood. The wound they create is often larger and bleeds more freely than other fly bites, contributing to the intense pain felt upon contact. Deer flies are smaller and often have dark bands on their wings, while horse flies are larger and can be up to an inch long.
Biting midges are minute flies whose tiny size allows them to pass through ordinary window screens. They possess blade-like mouthparts that can inflict a disproportionately painful wound. They are commonly found near bodies of water and in damp environments, and their bites often result in red welts that can last for several days.
Health Implications of Fly Bites
The injection of the fly’s saliva can trigger an allergic reaction in sensitive individuals, ranging from intense itching and hives to systemic responses. Scratching the bite site creates a break in the skin barrier, which can easily introduce bacteria and lead to a secondary bacterial infection requiring medical attention. This is a common complication, especially with the intensely itchy bites of midges or black flies.
Some biting flies are capable of transmitting pathogens. For instance, deer flies are known to be mechanical vectors for the bacterium that causes tularemia, often called “rabbit fever,” in the United States. This transmission occurs when the fly feeds on an infected animal and then transfers the bacteria to a human during an interrupted blood meal. Stable flies have been implicated in the mechanical transmission of diseases, primarily affecting livestock but posing a low risk to humans.
In the event of a bite, immediate care is recommended:
- Cleaning the wound with soap and water to reduce the risk of secondary infection.
- Applying an ice pack to help manage localized swelling and pain.
- Using over-the-counter antihistamines to counteract allergic reactions like itching.
- Consulting a healthcare professional if there is a spreading rash, excessive swelling, or fever following a fly bite.