Robber Flies - Family Asilidae

This page contains pictures and information about Robber Flies that we found in the Brisbane area, Queensland, Australia.

Giant Robber Fly - one of the largest fly species with wing-spans up to 75mm

The Robber Flies are air hunter. They also known as an Assassin Fly and Bee Killer. They have strong legs which can catch prey on flight. They are medium to large size flies with large eyes and necked head. They are active predators on flying insects, unselective in prey species. They even prey on web weaving spiders. Their mouthparts are the triangular proboscis  which insert into prey and suck the juice.

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Bee Killer                                                              Spider predator

Their larvae live in soil and rotting wood and are predaceous on other insect larvae.

Robber Flies can be found in forest, bushland and garden. We found quite a number of different species, although most of them we cannot identify to species level.

Subfamily Asilinae

Cerdistus constrictus, subfamily Asilinae, body length 25mm
Most Robber Flies are reddish-brown in colour. Different species that we found are looked similar and hard to be identified. Their mouthpart is the large pointed proboscis. Their thorax and legs are hairy. Their abdomen are long and thin. They are commonly seen in our backyard and in the bushes in Brisbane.
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? Neoitamus sp. , body length 25mm
Most Robust flies are with noticeable "beard" of setae around the face. It is believed that they serve as protection to their face from damage by their prey.
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The above pictures show the Robust fly mating pair. We can see that the male and female are look similar.
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? Neoitamus sp. body length 20mm
Robber flies are active predators. They usually rest on leaf or stick about one to two meters above ground, watching if there is any prey flies pass. Robber flies will capture prey by their powerful legs in mid air and consume while on the wings.
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? Ommatius sp., body length 15mm 

Subfamily Leptogasterinae

Robber Fly
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Leptogaster sp., body length 15mm

Subfamily Dasypogoninae 

Wasp-mimic Robber Fly
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? sp., body length 25mm
In mid summer we found this Wasp Mimic Robber Fly hunting on the ground among the dry leaves in Mt Cotton bushland. At first we thought it was a wasp and put those pictures in our Vespid Wasps page. Rob Longair, University of Calgary, send us email and  advised that "It is actually a robber fly (Diptera: Asilidae) mimic of a wasp. The antennae and the stance in the second picture are typical of robber flies." Here we would like to thank Rob again.
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During mid-summer in the rainforest near Mt Nebo, we found this Wasp-mimic Robber Fly mating pair.
Giant Robber Fly
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Phellus olgae, body length 45mm 
This is one of the largest fly species with wing-spans up to 75mm. We saw this fly once in Daisy Hill Forest during later summer. It was resting on a large tree trunk. We noticed the fly by its large compound eyes and golden hairs on its face. It flied fast in short distance with loud buzzing sound.
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The Giant Robber Fly has a dark brown body, a pair of golden brown wings, black long and strong legs with short dense golden yellow hairs.

Subfamily Laphriinae

Zebra Robber Fly
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? sp., body length 20mm
The Robber Flies have alternating black and white strips on body so we called them Zebra Robber Flies. We saw them once in Karawatha Forest during mid summer.
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This Rubber Fly waits for prey on tree trunk.
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Robber Fly
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? Laphria sp., body length 20mm
This Robber Fly likes to rest on the floor of footpath. We saw many of them in the rainforest near Mt Nebo. The Robber Fly in the above photos had just captured a small black wasp.

Robber Fly Attacked Spider

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Leptogaster sp., subfamily Leptogasterinae, body length 15mm
Insects are not always be the prey of spiders. Some insects attack spiders. Robber Fly is one of those insects. On a early summer day afternoon, a medium size Silver Orb Wed spider was building its web. The spider had finished laying the frame threads and radius of the web and about to put on the sticky spiral silk. There was a medium size Robber Fly flying over the spider web. After the fly circled two rounds, it attacked the spider on its abdomen. The fly punch its mouth parts into the spider body. There was only very little struggling, then all become motionless. The Robber Fly start feeding the spider on the unfinished spider web. We believed if the spider web were finished, the Robber Fly may not win so easily.
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Robber Fly feeding on spider, fly body length 12mm.
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Last updated: March 08, 2005.