A Bumblebee Mimic Robber Fly (Laphria macquarti) hunting. June 26th 2018, Smithsonian Environmental Research Center, Edgewater, MD.
Robber flies (Asilidae) are predatory insects. Adult forms of both sexes launch grasping aerial attacks on other insects, including stinging insects such as bees and wasps. For this reason they are also known as ‘bee catchers’. Foraging occurs in sunny habitats. They are seldom found in deep woods where it is dark. Here in this observation, the habitat is an exposed sunny edge of the forest. These insects become active during the hottest part of the day. The activity-threshold temperature is different for each species. For most species activity temperature threshold is above 20°C. Their activity is greatly reduced or absent in overcast weather, proportional to the activity of other prey insects. Their general habit is to perch in open sunlit areas where they presumably command a good view of passing insects. The genus Laphria evolved to mimic bees.
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Immediately upon interception, the asilid stabs its prey with its hypopharynx in the neck between the head and thorax, at the junction of thorax and abdomen, through the eyes, or between the sclerites at the end of the abdomen. The fly injects saliva containing neurotoxic and proteolytic enzymes into the prey. Enzymes rapidly immobilize the prey and digest its tissues. The asilid then sucks out the contents.
Females of some species take larger prey than that of males, but no sex differences have been noted for other species. Females also spend more time seeking prey than do males, possibly because of their higher investment on egg production.
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