Grey-legged Slender Fly
Orange Slender Fly
Orange-legged Slender Fly
Line-legged Slender Fly
Brown-legged Slender Fly
Black-legged Slender Fly
Wasp-mimic Robber Fly I
Wasp-mimic Robber Fly II
Zebra Robber Fly I
Zebra Robber Fly II 


Robber Fly Biology - Family Asilidae

Order Diptera

This page contains pictures and information about the biology of Robber Flies that we found in the Brisbane area, Queensland, Australia.
The Robber Flies are air hunter. They also known as an Assassin Fly and Bee Killer. They have piercing mouth-parts and 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. Robust flies prefer sunlit area to capture their prey.
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. Anyway, they usually attack from the back side of their prey. 
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Bee Killer                                                             Spider predator                                                    Prey on other insects
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 slender. They are commonly seen in our backyard and in the bushes in Brisbane.
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Mimicking Wasps 
Quite a number of Robust flies species mimic wasps. Some of them are from the subfamily Dasypogoninae.
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The mating pair                                                    The mating pair                                                      Taking off 
Female robber flies deposit creamy colour eggs on plants or in gaps within soil, bark, or wood. Egg-laying habits are different depend on species and habitat. Most species lay eggs in masses and are covered with protective coating. Robber fly larvae live in the soil or in rotting wood. Larvae are either predatory or parasitic, they feed on eggs, larvae and other soft-bodied insects. 
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Robber fly pupa empty case
They pupate in the soil and move to soil surface emerge as adults (We have the Giant Robber Fly egg-laying observation in this page).

Robber Fly Attacked Spider

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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. 

Robber Fly infected by fungus

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We found a number of times that this species robber fly was dead and resting on grass or stems. On the body the growing fungus can be seen. 
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We saw the fungus infections on other robber fly species, but seldom on other insects. Although we do found other fungus infections on spiders. 
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1. Insects of Australia, CSIRO, Division of Entomology, Melbourne University Press, 2nd Edition 1991, p 757.
2. Insects of Australia and New Zealand - R. J. Tillyard, Angus & Robertson, Ltd, Sydney, 1926, p362.
3. Giff Beaton's Robber Flies (Asilidae) of Georgia and the southeast - by Giff Beaton, 2005.
4. Family ASILIDAE - Australasian/Oceanian Diptera Catalog - Web Version, by Greg Daniels.
5. Family ASILIDAE Robber Flies - Australian Biological Resources Study, Australian Faunal Directory.

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Up ] [ Biology ] Laphriinae ] Ommatiinae ] Asilinae ] Bathypogoninae ] Phellinae ] Dasypogoninae ] Leptogasterinae ] Brachyrhopalinae ] Unidentified Robber Fly ]


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Last updated: October 25, 2012.