What Bug Is That? The guide to Australian insect families.

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A remarkably diverse, highly speciose, cosmopolitan family, probably still engaged in an evolutionary radiation. All are parasitoids of other arthropods, a niche that they have exploited with remarkable success. Due to the parasitic habit, they no doubt act as a strong controlling agency of other insects, including many pest species. However, they have provided relatively few useful agents for biological control.

All four subfamilies occur in Australia, with some 500 species already described, but the fauna may actually total at least twice that number. Of described species, only about 45 are Phasiinae, notably species of Alophora and Cylindromyia . There are some 90 species of Tachininae in about 30 genera, with significant numbers only in the endemic Chaetophthalmus and   Microtropesa . This compares strongly with New Zealand, where there has been a profuse radiation of Tachininae at the generic level. The bulk of our fauna falls in the Dexiinae and Goniinae, with about 200 described species each. The former includes some 50 species of the large, handsome metallic species of Rutilia ; the latter and many species of genera such as Carcelia and Exorista have distributions extending into in the Oriental Region and beyond.

All species are (as far as known) parasitoids of other insects - or perhaps, very rarely, of other arthropods such as centipedes. The soft-bodied larvae (caterpillars) of a wide range of Lepidoptera are by far the most commonly recorded hosts, but this may reflect the great popularity and ease of rearing. Larvae of Coleoptera are harder to come by, but nevertheless there are many recorded rearings - especially from those of leaf-eating Chrysomelidae and Curculionidae. The large, handsome Rutiliini seem to favour the soil-dwelling 'white-grub' larvae of Scarabeidae. Other orders are not immune: species of Froggatimyia commonly attack sawfly larvae (Hymenoptera: Pergidae) and others attack vespid wasps;  several genera attack Orthoptera (grasshoppers, stick insects, cockroaches), while Phasiinae seem to parasitise only Hemiptera.

Froggatimyia attacks its hosts in two main ways: (a) by depositing on or near the host an active larva or a rapidly hatching egg; the larva then bores its way into the host's body; or (b) by depositing small eggs on the host's food plant; these hatch when ingested. Commonly, only a few eggs or larvae are deposited at a time, but Rutilia spp. may lay many hundreds, which are scattered on the soil to actively seek a grass-grub as host. The Ormiini are remarkable for the gross expansion of the prosternum into a bladder-like organ; this seems to act as a resonating chamber that helps detect the song of the host katydid (Orthoptera: Tettigoniidae).


Most adults are fairly stout, bristly flies, of the general 'blowfly' type, though some are smooth-bodied, some Phasiinae are tiny, and there are also a few wasp-mimics. The diversity in details of structure and chaetotaxy makes the family difficult to characterise: vein M is usually curved or bent in an anterior direction, but there are exceptions; the antennal arista is usually bare, but in many Dexiinae it is plumose; in a single genus the eyes may be bare or profusely haired; etc. The one stable, characteristic feature is the strong development of the subscutellum as a rounded, fully sclerotised lobe. This occurs also in Gasterophilidae, Oestridae and Calliphoridae-Ameniinae, but these are easily distinguished on other characters.


As parasites, the distribution of tachinids is determined by that of their hosts. Some are cosmopolitan, or range widely over practically the whole continent. Others seem to have restricted ranges in, say, Tasmania, but that may be an artefact of collecting. Generally, little can be said until the fauna is studied in much greater detail.

  • Microtropesa sinuata

  • Rutilia sp.

  • Tachinidae

  • Tachinidae

  • Tachinidae