Phylum Arthropoda
Subphylum Hexapoda
Class Insecta
Order Diptera
Common name: flies
Overview
Diptera, or flies, are a huge order of commonly encountered flying insects, including mosquitoes, black flies, midges, fruit flies, blow flies and house flies. The major characteristic that distinguishes flies from most other insects is that adult flies have only one pair of functional wings. Their hindwings are reduced to small, club-like structures (halteres) that function as balancing organs during flight. A few species have lost their wings (and halteres) altogether. Flies typically have large compound eyes and sucking or sponging mouthparts for fluid feeding; the mouthparts are sometimes modified for piercing as in mosquitoes. In many species that do not feed as adults, the mouthparts may be absent, or reduced and non-functional. Dipterans have a variety of antennal types, ranging from short and simple, to thread-like, antler-like, feather-like, or hair-like, with or without a swollen base. Diptera are divided into two suborders. The Nematocera are generally small, delicate insects with long antennae, such as mosquitoes, crane-flies and midges. The Brachycera includes more compact, robust flies with short antennae, such as blow flies. Adult flies vary greatly in size: wingspans range from 1�75 mm. Fly larvae, some of which are commonly known as maggots or wrigglers, are typically grub-like, small, pale and soft-bodied, and lack true legs.
Distribution and diversity
Flies comprise a significant proportion of the arthropod diversity in most terrestrial habitats across the globe. They are found in almost all terrestrial and freshwater habitats across Australia; forests and the margins of water bodies have the greatest diversity of species. They are one of the four mega-diverse orders of insects, along with the Coleoptera, Hymenoptera and Lepidoptera. About 120,000 species of flies are described worldwide, and it is predicted that an equal number await description. For Australia, 6,430 described species are recorded but the true number is likely to be five times more.
Life cycle
Flies often mate while flying and in some species mating is preceded by a courtship dance. Sperm transfer is direct and parthenogenesis is rare. Egg development by the female often requires a blood or protein meal. The eggs are usually laid into a suitable substrate or close by an appropriate food source, for example in soil, organic matter, water, plant tissue or animal tissue. Live larvae are produced by some species. The larvae complete their development, usually through four larval instars, and pupate in the substrate where they were laid or in soil.
Feeding
With their sucking and piercing mouthparts adult flies ingest liquid foods. Species with sucking mouthparts typically consume nectar and other plant exudates and/or decomposing organic matter, using salivary secretions that liquefy the food. Species with piercing mouthparts such as mosquitoes and march flies pierce the skin of their prey with the proboscis and suck up blood. Dipteran larvae mostly feed on moist, decomposing food items such as carrion, fungi, dung and rotting vegetable matter, sometimes inside plant tissue (such as galls), while others are predators or parasitoids on a variety of insects, or are internal or external parasites of vertebrate hosts.
Ecology
Adult flies are free-living and ubiquitous, occurring in most terrestrial habitats as well as marine and freshwater environments. They are typically solitary, but they often group together around food sources and form swarms associated with mating behaviour. Depending on the species, adults can often be seen resting on or hovering over blossoms or patches of bare ground in the sun. In the house and garden many are associated with food and waste. Others, such as mosquitoes, prefer cool, dark places and are active at dusk and dawn. Flies are generally strong fliers with a rapid wing beat. Many are capable of hovering and most fly with a sharp, weaving flight. Some such as crane flies and mosquitoes are much slower fliers that float from side to side and buzz or whine in flight. Due to their abundance and diversity, flies are significant components of many ecosystems. Many adult flies feed on nectar from a wide variety of flowers and may be important plant pollinators, whereas the larvae of other species are important components of decomposition food webs. Parasitoids such as Tachinidae and predators like larval Syrphidae regulate arthropod populations in both natural and agricultural systems. A few herbivorous species have been used as biological control agents of weeds, and several species of biting flies are transmitters of the rabbit biological control viruses myxoma and calicivirus in Australia. Many species of Diptera are of medical and veterinary important due to the role they play in disease transmission and other health problems in humans, e.g. malaria, yellow and dengue fever, and domestic animals, e.g. blowfly strike and bot flies. Fruit fly, leafminer and stem borer species cause significant economic losses to agricultural crops.
Mosquito larvae South Perth, Western Australia
Image credit: Photographer: E.S. Volschenk
� Western Australian Museum
