Robber fly at rest.

Robber flies are opportunistic predators that seize their prey in flight.

Not all flies are a pest

Flies belong to the diverse Order Diptera, and a large proportion of these exhibit interesting as well as beneficial behaviour.

  • 29 November 2007 | Updated 14 October 2011

While the word 'fly' conjures up images of a frustrating summer BBQ or nasty day at the beach, not all flies are a nuisance.

Hover flies

Hover flies or drone flies belong to the family Syrphidae.

Many flies from this Family are easily confused with bees or wasps due to their characteristic yellow and black abdomen.

Some species, Ceriana and Eristalis are believed to mimic wasps or bees, possibly to avoid predation or to utilise the same food source.

Characteristics of adult syrphids include:

  • large eyes
  • very short antennae
  • fast fliers.

Some species are important pollinators and can often be seen hovering horizontally (like a miniature humming bird) above vegetation on warm sunny days.

While warmer weather brings out many well-known pesky flies around our homes, other species perform a useful service around the house and garden.

The larvae of some species of syrphid:

  • are efficient predators of aphids
  • are found in stagnant aquatic environments such as drains and ponds.

Those from the genus Eristalis are often described as a maggot with a tail and appropriately called ‘rat-tailed’ maggots.

The tail is a breathing siphon enabling larvae to remain submerged and protected while taking in air at the water surface.

Robber flies

Robber flies belong to the family Asilidae.

The Asilids are a diverse family of predatory flies.

At rest, adult robber flies may be mistaken for dragonflies as they have similar characteristics including:

  • strong outwardly positioned legs
  • solid thorax
  • large eyes
  • long skinny abdomen.

However, robber flies have only one pair of wings which are held over their back when resting, unlike dragonflies, who have two pair and hold them out to the side.

Similar to members of the syrphid family, some species of robber fly are also thought to mimic wasps.

Adult robber flies:

  • feed on other insects
  • are adapted to snatching fast flying insects on the wing
  • live in open forests.

Robbers flies hold their prey with powerful legs while neurotoxins and special enzymes (proteolytic) are injected into the victim. The body juices are then sucked out via a sharp straw-like mouth part (proboscis).

Larvae of robber flies live in soil or decomposing wood. The larvae of some species are also predacious.

Crane fly resting on fern leaf in the shade.

Crane flies are sometimes mistaken for giant mosquitoes.

Hover fly resting on a white flower.

Hover flies can be easily confused with bees and wasps.

Crane flies

Crane flies or daddy-long-legs flies belong to the family Tipulidae.

The Tipulidae is the largest Family of flies in Australia, with 704 known species.

Crane flies may be confused with super-sized mosquitoes, although lucky for us this isn’t the case.

Due to the size of some of these flies, the characteristic halteres found in all flies, may easily be seen.

Crane flies can also be identified by their long thin legs and hovering or buoyant flying behaviour.

Most species of adult crane flies drink but do not feed during the adult lifecycle. Other characteristics may include a preference for moist environments such as:

  • overhanging banks
  • rock shelters
  • shaded plants.

One species has adapted to resting on spider webs, possibly to gain protection from other insect predators using the web or spider itself.

Larvae of crane flies feed on decaying vegetable matter and can be found living in:

  • water
  • damp soil
  • decomposing matter.

Learn more about Fly, mosquito and midge (Diptera) research at CSIRO.

  • Colless DH, McAlpine DK. 1991. Diptera. In: The Insects of Australia: A textbook for students and research workers. Chapter 39. Second Edition. Vol 2. Melbourne University Press and Cornell University Press. Pp. 717-786.
  • Zborowski P, Storey R. 1995. A Field Guide to Insects in Australia. Chatswood, NSW. Reed Books.