Overview
Asilidae is a species-rich family of predatory flies, commonly known as robber flies. About 340 described species occur in Australia, but the total number of species is much higher. Some 80% of Australian asilid genera are endemic. The remainder, for example
Laphria
and
Leptogaster
, are more or less cosmopolitan.
The adults, which live mainly in open forest country, are aggressive predators, feeding particularly on Diptera and Hymenoptera, but attacking almost all insects, including dragonflies; even the hand of the collector is not immune! The prey is usually caught on the wing and held by the powerful legs; neurotoxins and proteolytic enzymes are injected, and the body juices of the prey are sucked out via the sharp proboscis (Kahan 1964). Eggs are laid in the soil, or attached to foliage or bark; many Asilinae oviposit in seed-heads of grasses. The larvae are cylindrical, elongate, tapered at each end, and have a small, distinct head. They are predators in soil or rotting wood.
Description
The shape of the head, with its prominent, well separated eyes, is very characteristic. Most species are bristly, with strong legs, short, stout thorax, and long, but stout, tapering abdomen; though some have the abdomen narrow and elongate. The venation is rather generalised, with both R and M four-branched, specialisation being towards apical fusion of R2+3 with R1, M3 with M4, or CuP with 1A. Most asilids are of moderate size, but there are tiny species of Stichopogon with wing length of only 1.7 mm, while Phellus and Blepharotes include the giants of Australian Diptera, with wing-spans up to 75 mm. Some species, particularly in the Dasypogoninae (sens. lat.), have orange or yellow markings on wings or body, and are effective mimics of sphecid and vespid wasps.
Distribution
Four subfamilies of asilids are recognised (from 2 to 6 or more, according to various authorities). The Asilinae, with 1-segmented palp, slender antennal style, and cell R1 closed and apically petiolate, are well represented here by species of
Colepia
,
Zosteria
,
Cerdistus
,
Ommatius
and others, including the giant species of
Blepharotes
. The Australian Leptogasterinae, which differ in having cell R1 open to the costal margin, include only the delicate, elongate species of
Leptogaster
. The Laphriinae and Dasypogoninae have 2-segmented palps and a thickened terminal style, or none, on the antenna. The former, with cell R1 closed, comprise mainly the relatively stout, usually shiny metallic, species of
Laphria
, some of which are wasp-mimics. The Dasypogoninae, with cell R1 usually open, or with a strong terminal spine on the fore tibia, are the dominant group, including over half of the known Australian fauna.
Bathypogon
is possibly the most widespread and diverse genus in the family.