Meet 'Blepharotes', the giant Aussie fly with a killer lifestyle

Last week, while exploring a patch of forest near Caboolture Airport, I disturbed an enormous flying insect that whirred past my head and landed a short distance away in the undergrowth. My first impression was that of a large, dark metallic blue wasp which was carrying something. Raising my binoculars to my eyes, however, revealed that I was looking at a huge, predatory fly—the giant blue robber fly (Blepharotes splendidissimus).

What it was carrying was a poor, unfortunate scarab beetle, the spotted flower chafer (Neorrhina punctatum). It had been stabbed between its hardened wing cases by the fly’s mouthparts, receiving a dose of toxic, protein-destroying saliva in the process. With the beetle’s insides liquidized, the fly was slurping up the contents like some kind of entomological milkshake.

The beetle is no shrinking violet itself and is only a little smaller than your average Christmas beetle in the same family. Hopefully that puts the size of the fly into perspective!

Robber flies must be the stuff of nightmares for scarab beetles, because even as immature maggots living in the soil, many robber flies will still target scarab beetles, only in their grub form instead. The poor things can’t catch a break! Too many beetles, however, and the plants and trees begin to suffer, so in this regard, robber flies are true friends of the forest.

Speaking of the forest, this particular one was in its regrowth stage, featuring lots of nitrogen-fixing casuarinas and wattles amongst the occasional bloodwood. At the zone where the forest transitioned into paperbark wetland, I found the robber fly. Purported to inhabit rainforest and scrub, perhaps the dense vegetation at Caboolture replicates those environments in some way.

References:

Flies: The Natural History and Diversity of Diptera, Stephen A. Marshall, 2012, Firefly Books

Wildlife of Greater Brisbane, 2020, Chris Burwell, Christine Lambkin et al, Queensland Museum