Fly

A fly (pl. flies) is an insect of the order Diptera (from Ancient Greek δι- di- 'two' and πτερόν pteron 'wing'), named for the single pair of wings. The hindwings have evolved into halteres, organs that sense rotation, giving flies precise control of their flight. Diptera is a large order containing more than 150,000 species, including horse-flies, crane flies, hoverflies, mosquitoes and others.

Flies have a mobile head, with a pair of large compound eyes, and mouthparts designed for piercing and sucking (mosquitoes, black flies, and robber flies), or for lapping and sucking in the other groups. Their wing arrangement gives them great manoeuvrability in flight, and claws and pads on their feet enable them to cling to smooth surfaces.

Diptera is one of the major insect orders and of considerable ecological and human importance. Flies are major pollinators, second only to bees and their Hymenopteran relatives. Flies may have been among the evolutionarily earliest pollinators responsible for early plant pollination. Fruit flies are used as model organisms in research, but less benignly, mosquitoes are vectors for diseases such as malaria, dengue, West Nile fever, yellow fever, encephalitis, and other infectious diseases.

Taxonomy and phylogeny

Dipterans, or true flies, are holometabolous — this means they go through a dramatic change called metamorphosis during their life cycle. They belong to a group called Mecopterida, which also includes insects like Mecoptera, Siphonaptera, Lepidoptera and Trichoptera. What makes most true flies special is that they have just one pair of wings, unlike other insects that might have “fly” in their names but actually have two pairs. Some true flies, like louse flies, have even lost their second pair of wings.

Flies have been around since the Middle Triassic period, about 240 million years ago, and became very common during the Middle and Late Triassic. Early flies probably did not eat nectar from flowers — flowers didn’t exist yet! Instead, scientists think they might have eaten honeydew, a sweet liquid made by bugs that suck sap from plants. Flies’ mouthparts are perfect for lapping up such sticky drops. Over time, flies evolved in three big bursts, with many new species appearing in the Triassic, Jurassic, and Paleogene periods.

Flies live almost everywhere on land and are very numerous. Well-known flies include house flies, blow flies, mosquitoes, gnats, black flies, midges, and fruit flies. Over 150,000 species of flies have been officially named, and there are probably many more waiting to be discovered. Some flies, like mosquitoes and crane flies, have long, thin bodies and antennae, while others, like house flies, have shorter bodies and antennae. Many fly larvae grow in water, and some can survive in very harsh places — from glaciers to hot springs! Adult hoverflies are famous for looking like bees or wasps to stay safe from predators.

Anatomy and morphology

Flies are insects designed for flying, with bodies built for moving through the air. Their bodies have three main parts: the head, the thorax, and the abdomen. The head holds large, round eyes and antennas that help them sense their surroundings. Flies have one pair of wings on their middle body part, the thorax, and smaller balancing organs called halteres on the back part of the thorax, which help them stay steady while flying.

Flies can move very quickly and change directions fast, thanks to their special wings and halteres. They often fly straight and then quickly turn in new directions. Some flies can fly high up, while others stay close to the ground. Their bodies are shaped to help them fly efficiently and avoid danger.

Life cycle and development

Flies go through a complete metamorphosis with four stages: egg, larva, pupa, and adult. The larval stage can be long, while the adult stage is usually short, focused mainly on mating and laying eggs. Many fly larvae grow in protected places, such as water, decaying fruit, or inside other animals. These larvae have soft bodies and can dry out if exposed to air.

When flies become pupae, they change in different ways depending on the species. Some pupae show parts of the future adult, while others are enclosed in a tough outer shell. The adult fly's main job is to reproduce, and they can do this quickly and effectively, which helps flies become numerous during mating season.

Ecology

Flies, also known as dipterans, are found everywhere and play many roles in nature. Their larvae can eat plants, decaying matter, or even live inside other animals. Some fly larvae live in water, while others live on land. Adult flies usually feed on nectar or other liquids.

Flies have many ways to protect themselves from predators. Some look like bees or wasps to scare off attackers, while others live inside ant nests and smell like ants. Even though flies face many predators like birds, bats, and spiders, they have developed clever tricks to survive.

Human interaction and cultural depictions

Flies have played many roles in different cultures, both good and bad. In the traditional Navajo religion, Big Fly is an important spirit being. In Christian demonology, Beelzebub is called the "Lord of the Flies" and linked to the Philistines.

Flies have appeared in stories for thousands of years. In ancient Sumer, a fly helped the goddess Inanna when her husband Dumuzid was in trouble. In Egypt, flies were used as awards for brave soldiers and were thought to carry the souls of people who had died. In Greece, myths tell of a fly turning a maiden named Myia into a fly after she tried to seduce a sleeping god.

Flies also have practical uses. Some flies help control pests by eating other insects. Others, like mosquitoes, can spread diseases but many flies are important for breaking down dead things and cleaning the environment. Scientists often study a special kind of fly called Drosophila melanogaster to learn about genes and how living things grow and change.