Identification and benefits of encouraging hoverflies in field crops

There are 274 species of hoverflies (Family: Syrphidae) in the UK, of which six are important for biocontrol. 

Eggs are ovoid and laid singly or in groups, depending on the species.

Predatory larvae are coloured, unlike other fly larvae, which are white or dirty yellow.

Pupae can sometimes be found attached to leaves.

A variety of colours is found in adults, although species with predatory larvae are black with white or yellow spots or bands, like bees and wasps.

Shapes vary from slender to stout and size varies from small to very large (3.5–35.0 mm). They are characterised by their ability to hover.

This is a highly diverse group with wide-ranging life histories. Typically, generation time is one or several per year. Adults are highly mobile, capable of migrating hundreds of miles.

They are highly effective natural enemies because of their mobility and short generation time. Aphids are the predominant prey of species with predatory larvae. Each can consume up to 1,200 aphids. Larvae are largely nocturnal and are rarely seen on plants. Larvae of other species feed upon fungi, plant parts or detritus, or are aquatic. Adults feed on the pollen and nectar of simple open flowers, usually white or yellow, such as umbellifers and daisies, and assist with pollination. Six species are important for biocontrol, two of which are very abundant.

Numbers are declining, especially those species with just one generation per year.

Attract adults by planting appropriate flower-rich habitats, but they will only remain if suitable densities of aphid prey are available. Hoverflies feed on the flowers of annual arable plants (such as cornflower, chickweed, knotweeds and shepherd’s purse) and hedgerow plants (wild carrot, cow parsley, hogweed and white campion). In addition, flower strips can be established specifically for hoverflies in and around fields containing coriander, buckwheat, phacelia or alyssum.