July 2016

Robber Flies

What is the name of these insects we have photographed?

Answer

Reburrus bancrofti. Photo courtesy of Aubrey Podlich Neosaropogon princeps. Photo courtesy of Sandra McEwan

The insects in your photos are flies known as Robber Flies, in the family Asilidae. These predatory flies are highly visible and ideal photographic subjects as they often sit out in the open sunlight on exposed branches or stems where they have a good view of other flying insects.

Their vision is excellent and they snatch their prey on the wing and then return to a ‘perch’ where they kill their prey by injecting toxic saliva into its body. The saliva liquefies the internal parts of the prey and the Robber Fly then sucks the prey dry.

All species have a moustache, a bunch of long hairs below the antennae, and are the only group of flies to have this character (clearly seen in the Reburrus image). The moustache seems to protect the fly’s face while it grapples with prey. This feature, combined with their large eyes and sharp strong piercing mouthparts, distinguishes the robber flies.

Ommatius mackayi. Photo courtesy of Scot McPhie

Robber Flies can be so intent on feeding or mating – or both at once! – that they ignore their surroundings, including the lucky photographers who took these excellent close up photos and sent them to the Queensland Museum.

One of these photos depicts a species of Robber Fly that mimics the black and orange colour pattern of many wasps. This is a fine example of the evolutionary process known as ‘Batesian mimicry’ in which a harmless species mimics the appearance of a dangerous species.

There are 340 described species of Robber Fly in Australia, and more than 7000 species known world-wide. Many remain to be described and a Queensland Museum Honorary is currently working on the taxonomy of the group.

The very large species take large insects like cicadas and jewel beetles and small species prey on smaller insects like flies, wasps, and even aphids and small spiders.

Despite their conspicuous presence as adult insects, little is known of their life history. The few known larvae of Australian species consume beetle larvae, both in the ground and in small branches.

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