There are over a hundred thousand species of true flies in the world and as varied as they are, they all share an important characteristic: all have only two membranous wings. The second pair of wings have been altered into mini-gyroscopes called halteres that assist flies with aerial manoeuvres, including being able to fly upside down or backwards. Because they have only two wings, they are usually recognisable as flies. They are divided into three suborders.
Suborder Nematocera
The first suborder are the Nematocera or thread horned flies. There are 22 families in this suborder of delicate flies with long, thin bodies, long slender legs and equally long and slender wings and antennae. Their larvae have hard head capsules and biting jaws and live in water. They go through 4 instars before pupating into adults. Blackflies, gnats and midges all belong to this suborder as do craneflies and mosquitoes.
The mosquitoes are the most important economically because of their blood sucking habits that have been exploited by parasites which use the mossies as an intermediate host to reach their primary mammalian hosts. Millions die each year of mosquito-borne diseases such as malaria and yellow fever. dengue fever and encephalitis.
Suborder Brachycera
The second suborder is the Brachycera or short horned flies, with 18 families. As their name indicates, brachycerans have short, stout antennae. Their larvae are sometimes aquatic,sometimes not, they have partially hardened heads and go through 5-8 instars. Bee flies, horse flies and robber flies are all brachycerans.
Suborder Cyclorrhapta
The third group is the largest and consists of the ‘higher’ flies, the Cyclorrhapta. These flies have short, three-segmented antennae. The larvae are legless maggots that feed with mouth hooks and pupate inside the last larval skin, known as the puparium. There are two groups within the Cyclorrhapta. The first is the Aschiza or hover flies, with six families. The second is the Schizophora, with 68 families. Fruit flies, leaf miners, blow flies and blue bottles, dung flies, house flies and botflies are all in this group, as are deerflies and keds. They are heavily bristled, not only on the body but also on their legs.
Within these three groups, one can find enormous diversity in body types, life styles and life cycles. They use all sorts of strategies to find mates and their larvae vary in appearance and life style more than in any other insect group.
Despite their bad press, many flies are beneficial. Many are important pollinators of plants for instance. They fulfill almost every role in the food chain, being flower feeders and herbivores, predators, bloodsuckers and parasites as well as scavengers. They are as widespread as they are diverse, being found on every continent and in every ecosystem. They make up one quarter of all the insects in temperate zones. They are not as pretty as butterflies but they are certainly as important.
