Thursday, 24 April 2014

Hornet Robber-fly

Asilus crabroniformis

22-29mm
Mid June to October
Large predatory robber-fly now restricted to a handful of locations in southern England. Very localised where it occurs in or around rough grazing pastures, often preferring sites with a good mix of wildflowers. Unimproved grassland - and lack of pesticide use is vital to this species.

 Female

 Male

Mainly seen perched on old dung or atop a ‘lookout’ spot on vegetation from which it darts out to grab passing prey, often dung beetles, smaller flies, butterflies or grasshoppers. When disturbed, short darting flights are made close to the ground to hop to another perching spot, appears very wasp-like in flight.


Mating pairs

Wings are clouded orange-brown with darker markings towards edges,very bristly body with strong legs and tarsal claws.
Both sexes are equally sized but females may appear more bulky. Males have a club ended abdomen whereas the female abdomen ends in a pointed ovipositor which is used to lay eggs in large animal dung. The larvae are also predatory, feeding on beetle larvae and other small invertebrates within the dung and surrounding soil.

 One of two male specimens found dead in cattle grazing field on the isle of Wight, antennae are missing. 

Illustration - pigment liner, markers & acrylic, A4

Harmless, but will attempt to pierce skin with beak-like proboscis if handled.

One of the Britain’s largest fly species. 

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