Perfectly described in the Kaufman Field Guide to North America, robber flies “are to other insects what falcons are to other birds: swift predators on the wing.” They perch in open habitat waiting for flying prey. Once in their sights, the chase is on. A swift injection of toxins from a piercing-sucking beak immobilizes, and digestive enzymes allow the fly to suck the contents. Their larvae are also predators, but live and hunt in the soil.
Morgan, age 12, found this fly on their deck. Her and her mom snapped some photos together, conducted research on the internet, and arrived at the identification. Their photos showcase some of the adult characteristics: a long and slender body, with a tapering abdomen, a “beard,” large eyes with a trough between the tops, and long legs with thick spines.
Size: 5 – 30 mm and more, typically 9 – 15 mm
Photos by: Amy Scott Smith and Morgan Smith on 7/18/22 in Missoula, MT