Horse flies are insects found in various natural environments. They belong to the family Tabanidae, a diverse group widespread across many regions. They are frequently encountered near bodies of water and in wooded areas, particularly during warmer months. They are among the larger types of flies, with a distinct appearance.
Physical Dimensions and Appearance
Horse flies have a robust, stout body, with many species measuring 0.5 to 1.25 inches long. Some large species reach an inch in length, with wingspans up to 2.5 inches. Their bodies are often covered with small hairs. They display colors including black, gray, brown, and sometimes patterns with stripes or spots.
A prominent feature is their large, compound eyes, which often exhibit brilliant green, iridescent, or banded patterns of purple, green, or blue. These eyes cover a significant portion of their head. Female horse flies are larger than males, and their eyes are distinctly separated. Conversely, male horse flies’ eyes often nearly touch at the top of their head. Their powerful wings are generally clear or cloudy, though some species may have dark markings. They possess only a single pair of wings.
Factors Influencing Perceived Size
Beyond physical measurements, several factors contribute to the perception of horse flies as sizable insects. One element is their loud, distinctive buzzing sound during flight. This auditory cue signals their approach, making their presence noticeable. Their buzzing is among the loudest of biting flies.
Horse flies are characterized by rapid, powerful, and agile flight patterns, capable of covering significant distances. They are highly attracted to movement, body heat, and carbon dioxide emissions, which helps them locate hosts. They are most active in sunny areas and frequently follow moving objects, displaying persistent host-seeking behavior.
The impact of their bite amplifies their perceived largeness. Female horse flies require blood meals for egg development and possess specialized blade-like mouthparts. These mouthparts cut through skin and blood vessels, resulting in a painful bite. The immediate discomfort and visible wounds, such as swelling and itching, caused by the bite contribute to the fly’s impression.
Distinguishing Horse Flies from Other Large Insects
Differentiating horse flies from other large insects involves observing several key features. Deer flies, which are closely related, are smaller than horse flies, measuring 0.25 to 0.5 inches long. A primary distinction lies in their wings: deer flies often have dark bands or spots, whereas horse flies usually have clear or uniformly dark wings. Deer flies may have spotted eyes, while horse flies have solid or striped eye patterns. Deer flies’ antennae are long and slender, contrasting with the shorter, thick-based antennae of horse flies.
Compared to bumblebees, horse flies superficially resemble them in size and robust build, but a clear difference is the number of wings. Horse flies, like all true flies, possess only one pair of wings, while bumblebees have two. Bumblebees are notably hairy, a characteristic not as pronounced in horse flies.
Horse flies are much larger than common house flies, which measure around 0.25 inches long. House flies have dull gray bodies and reddish eyes, unlike the robust, varied-colored bodies and often iridescent green or purple eyes of horse flies. House flies have sponging mouthparts and do not bite, serving as a nuisance. Female horse flies have blade-like mouthparts capable of delivering a painful bite.