True flies have only one pair of membranous wings (a few parasitic species are wingless)
The hind wings have been reduced to form club-shaped halteres or gyroscopic balancers. These are most easily seen in the crane flies or Tipulidae (see below). Without halteres flies just fall to the ground.
Flies are Holometabolous, i.e. have 4 distinct life stages, egg, larva, pupa, and adult.
Over 152,000 species have been described world wide, but many more are awaiting description.
Over 19,000 species are found in Europe.
over 7, 000 species are found in the UK.
They are of huge medical and veterinary importance both for good and bad. Millions of humans die each year from malaria, yellow fever, sleeping sickness and other diseases caused by parasites carried into the human by flies when they suck blood. And were it not for the scavenging activity of flies we would be knee deep in dung and other decaying matter.
All are liquid feeders, but there is great variation in their mouthparts (see below).
Their antennae vary greatly in shape and size.
Most lay small, cylindrical eggs, which hatch to produce legless larvae.
They have chemoreceptors for taste and smell on their legs as well as on their mouthparts.
On the left is a fly belonging to the Tipulidae family, these are commonly known as daddy-long-legs or crane flies. There are around 15 000 species world wide, and 87 species in the British Isles.
The adults are fragile and slender ranging from 0.6 - 6 cm in body length. All adults have the same thin body shape, with narrow wings and long legs. The legs are shed easily if they are caught, but this does not seem to hamper the fly much as they cannot walk or run. You can tell the sex of an adult by looking at the tip of the abdomen - females have a pointed tip, and males have a blunt tip. You will often see a female hopping around over lawns, wet ground and even water. She is laying eggs.
They have the most inelegant flight of all insects, with legs left dangling and flapping in every direction. Consequently the legs get trapped in spider's webs and vegetation. In order for the fly to escape it simply snaps off the trapped leg and carries on. The loss of 1, 2 or even 3 legs does not seem to inconvenience the daddy long legs who is quite content to manage as long as it has 3 legs.
Right is the ovipositor. The eggs are small, oval and usually black. Each female can lay several hundred in grassland, moist soil, bog and even over water. On land she pushes her ovipositor into the soil, but over water she places the eggs on, or just below the surface. This is often at the side of a pond among the aquatic plants.
The adults are short-lived and feed on nectar and other fluids. In some of the smaller species the adult males gather together in small swarms to dance in the late afternoon, these are sometimes called bobbing gnats.
Some adult females have no wings or only small vestigial wings. They can be found in the autumn waiting on walls for males to find them. Many species are nocturnal and are attracted to lights.
Tipulid larva (above) are commonly known as leatherjackets and live in the soil, rotting wood, bogs, other moist habitats, and some are aquatic. Fully grown they can reach up to 40 mm long.
They are a very important food source for some birds, and can occur in great numbers. They can cause damage to lawns, and can be a pest where potatoes and oats are grown. They are usually grey or greyish-brown in colour.