Hoverflies are true flies in the order Diptera. They belong to the family Syrphidae, their most characteristic features is the presence of a longitudinal false vein in the wing. In Britain there are over 270 species recorded and numbers are boosted in some species due to migration to this country. The family is divided into three sub-orders and various tribes, although classifications vary.
The larger species are often brightly coloured and very common. Many any of these have ornate body patterns, often of black and yellow, said to mimic wasps and bees but are harmless. (Birds know not to attack a bee as they will be stung but observations using a tame spotted flycatcher, showed that hoverfly mimicry did not fool it – this bird could distinguish between bees and the black and yellow Syrphinae, readily eating the hoverflies.)
Like many other flies, males and females often look alike, having the same colouring, size etc. Exceptions are found especially among the drone flies, where females differ from the males. In some species it is possible to sex them as males have bigger eyes which come closer together at the top of the head, whle the females have much smaller eyes, placed farther apart.
Very few hoverfly species have long accepted common names. Unfortunately in recent years there was a move to introduce common names to species in an attempt to popularise them. This has now probably complicated the issue as some species now have a variety of, largely inappropriate, vernacular names which are not always widely known and agreed by all. For this reason we have used the scientific names (everyone agrees on these!), but mentioned the vernacular names for some of them.
We illustrate some of the larger hoverflies which can be most asily identified from external characteristics, although in some cases related species are difficult to tell apart without close examination. For a few species, most notably those in the genus Sphaerophoria, it is necessary to refer to the genitalia to confirm the identification and the identification is often very difficult in the large genus Cheilosia, which are mainly black hoverflies.
Like other flies, hoverflies go through all stages of insect life: egg-larva-pupa-imago. The larvae of hoverflies are remarkably diverse for just one family of flies. Some have adapted to aquatic life in extremely dirty water (including stagnant), eating all kinds of decaying materials. In order to breathe they developed a long pipe at the rear end of the body, which they stick into the air. Examples include the rat-tailed maggots (about 40 species). Other larvae hunt for plant lice or aphids. Over one third of hoverflies have larvae that eat aphids (over 110 species). Some live in decaying wood, or sap runs on live trees (33 species).