Giant Robber Fly
Efferia ?
Feeding on a Silver-spotted Skipper (butterfly) at Washington Park, Gila Co., Arizona, USA. 17 July 2016.
Asilidae -- Robber Fly Family
Robberflies are voraceous predators capable of taking large insects as prey. Very large robberflies often attract attention as they lumber off with a hapless butterfly or wasp in their clutches. When hunting or looking for mates they often perch upon a rock or bare soil in a walking path. Several very similar Promachus/Efferia are found in Arizona including at lower elevations among the sycamores or the desert scrub (thumb links below).
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