Overview
This is a compact, cosmopolitan family of around 300 described species, easily recognised by the wing venation. Most are large to medium-sized, compactly built flies, usually hairy but never bristly; typically the abdomen is conical, the 6th and subsequent segments in the female forming a tubular, retractile 'ovipositor' with a pair of strikingly elongate, 1-segmented cerci. The Australian fauna comprises just over 50 described species in seven genera.
The medium-sized to large, often rather ornate species of
Trichophthalma
are the most abundant of nemestrinid species. They are most often taken when feeding on blossom or hovering motionless over open sunny patches, darting away when disturbed, but usually returning quickly to the same spot. The larvae are parasitic, and those of
Trichopsidea oestracea
are found in grasshoppers (Fuller 1938).
Description
Adults are relatively large, stout flies that resemble Tabanidae in many respects. However, nemestrinids can be recognised immediately by the highly modified wing venation, with a complex composite diagonal vein in the wing comprising elements of R and M veins. In addition, many longitudinal veins in the wing are directed anteriorly, with all R veins and M1 and M2 meeting the wing margin anterior to, or at, the wing apex.
Distribution
Of the six genera definitely recognised in Australia,
Cyclopsidea
is a specialised endemic element,
Trichophthalma
is shared with southern South America, and the others are recent derivatives from the north (Paramonov 1953).