Criminals Amidst: Robberflies!

By Brigitte Howarth 26/10/2003

The images Bob was able to take of the mating flies is quite extraordinary as generally there is a lack of courtship and mating behaviour available for these flies. They belong to the order Diptera (flies), family Asilidae (robberflies). These are aptly named due to the behaviour of pouncing on unsuspecting insects.

Robberflies are large and powerful insects with highly specialized vision that enables them to see virtually all around. UAE species tend to sit on the ground, sand, stones or on vegetation and scan their environment. If an insect flies into the vicinity of the robberfly, it will reposition itself until it decides whether to attack or not. The asilid then takes off and pounces on the victim, grabs onto it and lands on the ground, piercing the victim with sharp mouthparts. Next the fly injects a poison which is a constituent of its saliva. This immobilizes the victim and starts digestion of the fluids in the victim which are then sucked up by the fly. The poison has been studied more closely and it has been found that injecting asilid poison into invertebrates kills them instantly (Adamovic, 1963).

Most UAE species are large and thus these flies are easily spotted. However, their identification is more difficult. Specimens taken to the BMNH in London three years ago were not able to be identified, despite being over an inch in length. If males are collected, their genitalia needs to be unhooked and exposed as these hold the clue to identifying the specimen further.

The robberflies photographed can clearly be distinguished as male and female. In this photograph, the fly on the left is the female. Females have a pointed abdomen whereas the males are slightly more bulbous. The fly on the right is the male and it is visible how the structures at the end of its abdomen are holding on to the female.

Formal identification of the species is in progress and will be added to the website in due course. The species is suspected of belonging to the genus Apoclea.

Bibliography

Adamovic Ž.R. (1963) Ecology of some asilid species (Asilidae, Diptera) and their relationship to honey bees (Apis mellifera L.). Bull. Mus. Hist. nat. Belgrade. 30: 1-120.

Stubbs A. & Drake M. (2001) British Soldierflies and their Allies. British Entomological and Natural History Society, ISBN 1-899935-04-5.

Walker D.H. & Pittaway A.R. (1987) Insects of Eastern Arabia. MacMillan Publishers, ISBN 0-333-43214-2.