Many people encounter large flies and wonder about their identity and habits. These insects, part of the diverse order Diptera, often appear much larger than common house flies, leading to curiosity or sometimes concern. Understanding the different types can clarify their presence and impact in various environments.
Identifying Common Large Flies
Several types of large flies are commonly encountered, each with distinct features. Horse flies and deer flies belong to the family Tabanidae and are known for their robust bodies and large eyes. Horse flies are typically larger, ranging from 10 to 25 mm, while deer flies are smaller, between 7 to 10 mm.
Crane flies, part of the family Tipulidae, are frequently mistaken for oversized mosquitoes due to their very long, slender legs and delicate, elongated bodies. Their wingspan can vary, with some species reaching up to 11 cm.
Robber flies (family Asilidae) are predatory insects with hairy, robust bodies and a noticeable depression between their compound eyes. Blow flies (family Calliphoridae) are robust flies, recognized by their metallic blue, green, or black coloration and noisy flight.
Key Distinguishing Features
Differentiating these large flies involves observing specific physical and behavioral cues. Horse flies and deer flies have large, often iridescent eyes that in males meet at the top of the head. Deer flies typically have mottled wings with dark patterns, while horse flies usually have clear or uniformly cloudy wings. Their bodies are stout and often drab brown, gray, or black.
Crane flies are distinguished by their extremely long, fragile legs that are easily detached, and a V-shaped suture on their thorax. Unlike mosquitoes, they have narrow, membranous wings that can have a smoky tint.
Robber flies feature a distinctive “beard” of bristles around their face, known as a mystax, along with strong, spiny legs for grasping prey. Blow flies are identified by their metallic sheen and bristly bodies. They have large, reddish-brown eyes and transparent wings that are held flat over their backs.
Behaviors and Ecological Roles
The behaviors and ecological contributions of these large flies differ significantly. Female horse flies and deer flies are known for their painful bites, as they require blood meals to produce eggs. They inflict deep wounds with scissor-like mouthparts, and their saliva contains anticoagulants that promote blood flow. While male horse and deer flies feed on nectar, females can transmit diseases like tularemia and anthrax, though this is rare for humans in many regions.
Crane flies do not bite humans or animals, as most adult species have non-functional mouthparts and do not feed. Their adult stage primarily focuses on reproduction.
Robber flies are predators that hunt other insects, including pests, by darting from a perch and injecting neurotoxins and digestive enzymes into their prey. They will only bite humans if mishandled.
Blow flies act as scavengers, playing a significant role in decomposition by laying eggs on carrion and decaying organic matter. Their association with waste can sometimes make them nuisance pests and potential mechanical vectors for bacteria.
Life Cycles and Habitats
All these flies undergo complete metamorphosis, progressing through egg, larval, pupal, and adult stages. Their habitats vary depending on the species and life stage.
Horse flies and deer flies lay eggs on vegetation near water, and their larvae are semi-aquatic, developing in moist soil, mud, or shallow water. Adults are often found near water bodies or wooded areas.
Crane fly larvae, often called “leatherjackets,” typically live in damp soil, decaying vegetation, or aquatic environments. Adults are common in grassy areas, gardens, and near lights, often emerging from late winter to early spring.
Robber fly larvae reside in soil or decaying wood. Adult robber flies prefer open, sunny areas and are often seen perched on vegetation or fences.
Blow flies lay their eggs on carrion, decaying organic matter, or sometimes in wounds, where the larvae (maggots) develop. Adult blow flies are widespread and attracted to various odors associated with decomposition.