Beneficials on farmland: identification and management guidelines (HGCA Summer 2008)

Flies (Diptera)

There are over 6,900 species of flies in Britain.

Two-winged, or true, flies have one pair of membranous wings.

Flies have sucking mouthparts, in some instances adapted for piercing. Shapes range from stout-bodied (house flies and bluebottles) to slender (crane flies and mosquitoes). There are also numerous smaller gnats and midges.

Predatory flies that commonly occur on farmland include hoverflies, dance flies, robber flies and long-legged flies.

Dance flies (Empididae)

  • Adults congregate in dancing  swarms, as do gnats
  • Small to medium-sized, bristly
  • Spherical head on slender neck
  • Horny proboscis to suck insides out of other flies
  • Larvae are partially predatory and live in decaying vegetation or water

Dance fly eating orange wheat blossom midge

Robber flies (Asilidae)

  • Some 28 UK species
  • Medium to large, slender but strongly built
  • Powerful legs
  • Horny proboscis to pierce prey
  • Adults predatory on insects

Robber flies eat a wide range of food materials ranging from other insects, dead matter, vegetation to pollen and nectar.

depends on species

Hoverflies (Syrphidae)

  • Approximately 270 British species
  • Most are brightly coloured
  • Mimic wasps and bees
  • Adults feed on nectar and pollen
  • Many larvae found on farmland are predatory, especially on aphids
  • Fly long distances

Adults can be confused with wasps and bees; larvae with leaf beetle larvae.

Each hoverfly larva eats about 400 aphids on arable crops. A ratio of 1 larva: 30 aphids can control severe infestations.

Hoverfly (Episyrphus balteatus). Wild flowers in field margins attract hoverflies. Oilseed rape and other flowering crops attract large numbers.

Syrphid pupa

Long-legged flies (Dolichopodidae)

  • Over 280 species in UK
  • Small, bristly and metallic with long legs
  • Adults predatory on other smaller insects
  • Adults frequently visit flowers
  • Larvae live in humus or are aquatic and mainly carnivorous

Dolichopos wahlbergi

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