Flies are an incredibly diverse and widespread group of insects found across nearly every environment on Earth. Understanding their various forms and functions offers a fascinating glimpse into the natural world.
The Defining Features of True Flies
True flies belong to the order Diptera, a name derived from Greek words meaning “two wings.” Unlike most insects with four wings, true flies have only a single pair of functional forewings for flight. Their hindwings are modified into small, club-shaped structures called halteres. These halteres vibrate rapidly during flight, acting like gyroscopes to provide balance and stability, enabling aerial agility. True flies undergo complete metamorphosis, transitioning through four distinct life stages: egg, larva, pupa, and adult. Their larvae, often known as maggots, are legless and worm-like. Adult flies exhibit mouthpart adaptations, including sponging, piercing-sucking, or cutting-sponging, all designed for a liquid diet.
Long-Horned Flies: The Nematocera
The order Diptera is divided into two main suborders, with Nematocera representing the “long-horned flies.” These flies are characterized by slender bodies, long legs, and antennae composed of many similar segments. Their larvae have distinct heads and live in wet or aquatic environments.
Mosquitoes are characterized by slender bodies, long legs, and a proboscis for feeding. Female mosquitoes require blood meals for egg development, making them vectors for various diseases, while males primarily feed on nectar. Mosquitoes lay eggs in stagnant or slow-moving water. Their larvae, often called “wrigglers,” develop in aquatic habitats like ponds, marshes, and small containers of water.
Gnats include various small flies like fungus gnats and biting midges. Fungus gnats (family Sciaridae) are delicate, dark-winged flies, 1/16 to 1/8 inches long, sometimes mistaken for mosquitoes. They are found near indoor plants, as their larvae feed on fungi and organic matter in moist soil.
Biting midges (genus Culicoides), also known as “no-see-ums,” are tiny, gray, two-winged insects less than 1/8 inch long. Female biting midges inflict painful bites to obtain blood. Many species have wings patterned with dark and pale spots. They are found in coastal areas, marshes, and other wet, organically rich environments where their larvae develop.
Crane flies (family Tipulidae) are Nematocera, sometimes mistaken for giant mosquitoes due to their slender bodies, long legs, and sizes up to 3 cm or more. Despite their intimidating appearance, adult crane flies are harmless to humans and do not feed, though some consume nectar or water. Their larvae, known as “leatherjackets” for their tough skin, live in moist soil, decaying organic matter, or aquatic environments, feeding on decaying plant tissue or roots.
Short-Horned Flies: The Brachycera
The second major suborder of true flies is Brachycera, characterized by robust bodies and shorter antennae, with only three segments. This group includes many familiar flies. Their larvae have indistinct heads and live in diverse environments, including soil, rotting vegetation, or animal materials.
House flies (Musca domestica) are common Brachycera, measuring about 6 mm (0.25 inch) long and appearing grayish-black with four dark stripes on their thorax. They possess sponging mouthparts, enabling them to lap up liquids from decaying garbage, animal waste, and other organic matter. House flies are found globally in association with human habitation, resting on walls or ceilings indoors. Female house flies lay eggs in moist, decaying organic material, with larvae (maggots) hatching quickly and feeding on the same decaying matter.
Fruit flies (genus Drosophila) are small, tan and black, often with distinct red eyes, and about 1/8 inch long. They are attracted to ripened, decaying, or fermenting fruits and vegetables, where females lay eggs. Fruit fly larvae feed on sugary fruits and fermenting masses. These flies are found in kitchens, restaurants, and other places where food is processed or stored.
Horse flies (family Tabanidae) are large, heavy-bodied flies, black or gray, ranging from ¾ to 1¼ inches long, with large, often bulgy eyes. Female horse flies inflict painful bites, possessing scissor-like mandibles that cut into skin to feed on blood, required for egg production. Males primarily feed on nectar and plant juices. Horse flies are found near water and damp soil in brushy or pasture areas. Their larvae are aquatic or semi-aquatic, developing in wetlands, mudflats, or near ponds and streams.
Hoverflies (family Syrphidae) mimic bees or wasps with their yellow and black striped bodies, but they are true flies and do not sting. These agile fliers hover over flowers, feeding on nectar and pollen. Their larvae exhibit diverse feeding habits, with some preying on aphids and others living in decaying organic matter.
Blow flies (family Calliphoridae) have bright, metallic bodies, appearing blue, green, gold, or shiny black, and measuring around 1/5 inch. They are attracted to decaying organic matter, particularly dead animals and garbage, using antennal sensors to detect odors from great distances. Female blow flies lay eggs on carcasses or other rotting materials. Their larvae (maggots) feed on this decaying flesh. Blow flies thrive in warm, humid conditions and are often the first insects to arrive at a decaying food source.
The Surprising Diversity and Importance of Flies
Flies exhibit diversity with over 120,000 described species globally. They inhabit nearly every ecosystem, playing numerous roles. Flies contribute to ecological processes, serving as decomposers, breaking down organic matter and recycling nutrients. Without flies, the natural decomposition of waste and dead organisms would slow.
Many fly species also act as pollinators, transferring pollen between plants as they feed on nectar. Some flies pollinate crops, including apples, strawberries, carrots, and onions. Flies are a food source for animals, including birds, amphibians, spiders, and other insects, supporting food chains within ecosystems. Their presence and activities are important for the health and functioning of natural systems worldwide.