Horseflies are large, biting insects commonly encountered in warm weather, particularly near livestock and water sources. These robust flies, belonging to the Tabanidae family, are a noticeable nuisance during their active seasons. Understanding their characteristics and behaviors helps explain why they are often considered bothersome pests.
Identifying Horseflies
Horseflies are larger than common houseflies, typically ranging from 6 to 25 millimeters (0.25 to 1 inch) in length, with some reaching up to 30 millimeters (1.25 inches). They possess stout bodies that can be dark brown, black, or grayish, sometimes with stripes on their backs or chests. Their wings are often clear, though some species, like deer flies, may have dark patterns or bands on their wings.
Their large, prominent compound eyes are a distinguishing feature, which can be iridescent and display vibrant colors such as green, purple, or metallic sheens. These eyes allow them to detect movement across a wide range of angles to aid in pursuing hosts. Their antennae are short, typically shorter than their head, and composed of three segments.
Understanding Horsefly Bites
Only female horseflies bite, as they require a blood meal to produce eggs. Male horseflies, in contrast, primarily feed on nectar and plant exudates.
The painful nature of a horsefly bite stems from their unique mouthparts, designed for cutting rather than piercing. Unlike mosquitoes that use a needle-like proboscis, female horseflies possess blade-like mandibles that act like scissors, slicing through the skin to create an open wound. They then use a sponge-like mouthpart to lap up the pooling blood. This cutting action, combined with the absence of an anesthetic injection, results in immediate, sharp pain.
The bite typically causes a raised, red, itchy welt, and sometimes bruising or swelling. Severe reactions can occur, including hives, dizziness, or wheezing, indicating an allergic response. Scratching the bite can also lead to secondary bacterial infections.
Minimizing Encounters
Horseflies are often found near water bodies like marshes, wetlands, and streams, which serve as breeding grounds for their larvae. They are also attracted to large, dark, moving objects and the carbon dioxide exhaled by mammals.
Wearing long-sleeved clothing and pants can protect exposed skin, though horseflies can sometimes bite through thinner fabrics. Light-colored clothing may offer an advantage, as horseflies are less attracted to lighter shades. Insect repellents containing DEET or picaridin provide some protection, though they may be less effective against horseflies than mosquitoes. Limiting outdoor activities during peak horsefly activity, often during the warmest parts of the day in summer, can also reduce encounters.
Managing Bites
Upon receiving a horsefly bite, clean the affected area immediately with soap and water to prevent infection. Apply a cold compress or an ice pack wrapped in a cloth to the bite for about 10 to 20 minutes to reduce swelling and discomfort. Elevating the bitten area can also help manage swelling.
Over-the-counter medications can alleviate symptoms. Topical hydrocortisone cream or oral antihistamines can reduce itching and inflammation. Pain relievers like acetaminophen or nonsteroidal anti-inflammatory drugs (NSAIDs) can be used for pain. Avoid scratching the bite to minimize infection risk. If symptoms such as spreading redness, pus, increased pain, or signs of a severe allergic reaction like difficulty breathing, dizziness, or widespread rash occur, medical attention should be sought.