Reddish-colored flies can be a common concern, as some species with red or reddish hues can pose health risks or be a nuisance. This article clarifies which flies fit this description and the threats they present.
Identifying Common “Red Flies”
Many flies people describe as “red flies” belong to groups known for their biting habits. Horse flies and deer flies, both members of the Tabanidae family, are frequently encountered reddish-brown or dark-bodied flies. Horse flies are generally larger (6-25 mm), dark brown or black with metallic sheen eyes. Deer flies are smaller (8-10 mm), often with brightly colored, iridescent eyes and dark bands on their wings. These flies are commonly found in wooded or forested areas near water sources like ponds, streams, and marshes, where their larvae develop in moist soil or aquatic environments.
Stable flies, resembling common house flies but with piercing mouthparts, can also appear reddish or dark. They are typically gray with dark stripes and spots on their abdomen, measuring 5-6 millimeters long. Often found near livestock facilities, they can also be present in open pastures and residential settings with decaying organic materials like pet droppings. Smaller flies, like fruit flies, may also be called “red flies” due to their red eyes, though their primary concern is nuisance rather than biting.
Understanding Their Threat
The primary threat from flies commonly perceived as “red” stems from their bites, as female horse flies, deer flies, and stable flies require blood meals to produce eggs. Horse fly bites are particularly painful because their scissor-like mouthparts cut into the skin to create a pool of blood, rather than piercing it. This can result in immediate sharp pain, swelling, and sometimes bleeding welts. Deer fly bites are similarly painful, and the anticoagulant injected by the female fly can cause severe allergic reactions in some individuals.
Beyond the immediate discomfort, these flies can mechanically transmit certain diseases, although human transmission is less common than with other vectors. Horse flies and deer flies have been associated with the transmission of tularemia, a bacterial infection, particularly in the western United States. While tularemia can be serious, its transmission by deer flies is considered minor compared to other routes. Stable flies can also mechanically transmit anthrax and have been implicated in the spread of equine infectious anemia (EIA) among animals, though they are not considered primary vectors for medically important human pathogens. The main concern for most people encountering these flies is the painful bite and localized reactions, rather than systemic disease.
Protecting Yourself
Personal protection against biting flies involves several strategies to minimize exposure. Wearing long-sleeved shirts and pants can help cover exposed skin, reducing available biting surfaces. Using insect repellents containing active ingredients such as DEET, picaridin, or oil of lemon eucalyptus can offer a layer of protection. While DEET is generally effective, some flies, like deer flies and horse flies, may be less sensitive to it, potentially requiring liberal application for satisfactory relief.
Environmental controls also contribute to reducing fly populations around homes and recreational areas. Since many of these flies breed in moist or aquatic environments, minimizing standing water and managing organic waste can disrupt their life cycles. For instance, stable flies lay eggs in moist, decaying organic matter like soiled bedding or spilled feed. Maintaining screens on windows and doors can prevent flies from entering indoor spaces. Avoiding areas where these flies are abundant, especially during their peak activity in warm months, can also help prevent encounters.
When to Seek Medical Advice
While most fly bites cause localized irritation, certain symptoms indicate a need for medical attention. Seek medical advice for signs of a severe allergic reaction, including difficulty breathing, tongue or throat swelling, dizziness, a fast pulse, hives spreading beyond the bite, or sudden weakness. These symptoms, especially if rapid, could signal anaphylaxis, a life-threatening condition.
Monitor the bite site for signs of infection. These include increasing redness, warmth, pain, or swelling around the bite, especially if a red streak extends from the area. Pus or drainage from the bite, along with fever, chills, or swollen lymph nodes, also suggests infection. If systemic symptoms like body aches, fever, or swollen lymph nodes develop after a bite, especially following travel to areas with fly-borne diseases, consult a healthcare provider.