Around 250 species of hoverfly have been seen in the UK, but only about 40 of these are commonly seen.
Hoverflies have one pair of wings, and a pair of club-shaped organs called 'halteres'. These move up and down, in time with the wings to help control balance in the air. Many species of hoverfly have markings which strongly resemble those of bees and wasps, so giving them some protection. Most hoverflies develop into adults later in the spring, and by this time most young birds have learned to avoid black and yellow insects because of the danger of stings.
The best time to look for most hoverfly larvae is at night or on wet days. They look like pink or green caterpillars about 5mm long. Some species of hoverfly larvae are aquatic, like those of the drone flies.