Flies are common in various environments, from homes to natural landscapes. While many categorize any small, winged insect as a “fly,” the world of flies is incredibly diverse, with unique characteristics. Understanding how to identify these types offers insights into their behaviors, habitats, and potential impact. This guide explores the defining features of true flies and provides tips for distinguishing common varieties.
What Makes an Insect a Fly?
True flies belong to the insect order Diptera, named for their “two wings.” This is their most defining feature, as they possess only one pair of functional wings for flight. Their hind wings have evolved into small, club-shaped balancing organs called halteres, which act like gyroscopes for stability and control during agile flight. Most other flying insects have two pairs of wings.
Flies undergo complete metamorphosis, with four distinct life stages: egg, larva (often called a maggot), pupa, and adult. Their larvae are typically legless and worm-like, developing in diverse environments such as water, decaying organic matter, or within plants and animals.
Key Anatomical Features for Identification
Identifying fly species relies on observing specific anatomical details. The head contains compound eyes, antennae, and mouthparts. Compound eyes are large, providing a wide field of view. Antennae serve as primary sensory organs for smell, varying in shape and length, and their structure differentiates species.
Mouthparts are adapted for liquid diets, ranging from sponging types, like house flies, to piercing-sucking types, characteristic of mosquitoes. The thorax bears the single pair of functional wings and the halteres. Wing venation, the pattern of veins, also provides identification clues. Body size, shape, and color patterns on the body and wings also contribute to identification.
Common Fly Types and How to Identify Them
Many common fly types can be identified by combining observations of their size, color, habitat, and specific anatomical features. The House Fly (Musca domestica) is a familiar species, typically dull gray and about 1/4 inch long. A distinguishing feature is the presence of four dark longitudinal stripes on its thorax. House flies also have large reddish eyes and sponging mouthparts, which they use to liquefy food. They are commonly found around animal feces, garbage, and decaying organic matter.
Fruit Flies (Drosophila melanogaster) are considerably smaller, usually about 1/8 inch long, with an oval body shape. They are often recognized by their typically bright red eyes, though some can have dark eyes, and a tan to brownish-yellow body with a black abdomen. Their wings are translucent, and their antennae have a feathery bristle. Fruit flies are frequently seen hovering around ripe or fermenting fruits and vegetables, as well as drains and garbage disposals.
Mosquitoes (family Culicidae) are slender insects, generally measuring 0.25 to 0.5 inches long, with long legs. A key characteristic is their long, needle-like proboscis, which females use for feeding. Mosquitoes also have scales on their wing veins and a fringe of scales along the hind edge of their wings, which can be seen with magnification. Their bodies are typically brown or black, and some species exhibit distinctive patterns, such as black-and-white bands on their legs or stripes on their thorax.
Drain Flies (family Psychodidae), also known as moth flies or sewage flies, are small, fuzzy insects ranging from 1/16 to 1/5 inch long. Their bodies and broad, oval wings are densely covered with hairs, giving them a moth-like appearance. When at rest, their wings are often held in a characteristic roof-like manner over their bodies. Drain flies are weak fliers and are typically found resting on walls near drains, where their larvae feed on the organic film inside pipes.