Landcare Research - Manaaki Whenua

Landcare-Research -Manaaki Whenua

FNZ 23 - Dolichopodidae (Insecta: Diptera) - Popular summary

Bickel, DJ 1992. Sciapodinae, Medeterinae (Insecta: Diptera) with a generic review of the Dolichopodidae. Fauna of New Zealand 23, 74 pages.
( ISSN 0111-5383 (print), ; no. 23. ISBN 0-477-02627-3 (print) ). Published 13 Jan 1992

Popular summary

The Dolichopodidae are one of the largest fly families in New Zealand, with 132 valid species and perhaps half as many again yet to be described.

These small insects are usually metallic blue-green in colour and slender in build, with rather long legs. They are commonly seen on leaves, tree trunks, river rocks, mudflats, intertidal reefs, and even window panes. Here they run about rapidly searching for prey and for potential mates. They favour moist habitats, and are often taken in large numbers by sweeping with an insect net. Since most are under 5 mm long, a microscope is needed to study them.

Adults are predatory on such soft-bodied invertebrates as mites, thrips, aphids, small aquatic worms, and even mosquito larvae, and are important general control agents of many pest species. Prey is crushed between a pair of hard, press-like mouthparts, and the body fluids of the prey are then ingested.

Dolichopodids are best known for their elaborate male secondary sexual characters - special modifications of body structures that enable the sexes of a species to recognise each other during courtship. These include flag-like flattening of the antennae and legs, modified hairs, elongation and deformation of legs, silvery patches that flash in the sunlight, and unusual wing veins. As a result of these modifications, males and females of a species often look strikingly different.

The maggot-like larvae of dolichopodid flies are found in soil, moss, decaying vegetation, and mud, and under bark. Most are predators or scavengers, although larvae of one genus are stem miners in various grass-like plants. Almost nothing is known of the immature stages of New Zealand species.

One of the strangest New Zealand dolichopodids is the flea-like Apterachalcus borboroides, the only member of its family in the world to have lost both its wings and its halteres (balancing organs). It is found only in the mountains of the South Island and the cold, windswept subantarctic islands. Another species from the subantarctic islands, Schoenophilus pedestris, has wings reduced to narrow straps, useless for flying. There is a general trend among insects for their flying ability to degenerate on cold, windy islands or high mountains, where flight is extremely difficult or costly in energy.

New Zealand's dolichopodid fly fauna is adapted to temperate and cool climates, and is broadly similar to the dolichopodid faunas of other Southern Hemisphere landmasses, especially Tasmania, south-eastern Australia, and southern South America. Because of its geographical position, no tropical groups of Dolichopodidae have been able to reach New Zealand.