The three eastern species are very similar, but can be distinguished by leg color and the extent of smokey shading on the wings.
Paul Bedell took me to his Nicocles pictus spot where we got to see several males displaying. These males would undulate their abdomens, causing it to “flash.” Combined with the smokey bands on the wings, one can see from this series how a nearby robber fly might perceive it.
Hind femora red. Other femora black. Wings entirely smokey, slightly lighter on apical third. Halteres yellow.
Size: 7-9 mm
Range: Southeast (North Carolina to Florida)
FL Range: Panhandle
FL Season: April, October-November
All femora entirely dark red. Wings with smokey dark spots near the wing veins on apical two-thirds. Abdomen pollinose laterally except on fifth segment.
Size: 10-12 mm
Range: Eastern U.S.
FL Range: Unknown
Season: January to April then again October-November outside of Florida.
Femora black except at apex. Apical two-thirds of wings dusky. Halteres brown. Fall flight season.
Size: 8-10 mm
Range: Eastern U.S. (Massachusetts to Florida)
FL Range: Panhandle and North Florida (Santa Rosa, Franklin, Duval, Alachua, Marion)
FL Season: October-November
Apical third of middle and apical half of fore femora black. Abdomen thinly pollinose throughout. Dark on wings only along veins – otherwise clear-winged.
Size: 9 mm
Wilcox, J. (1946): New Nicocles with a key to the species (Diptera, Asilidae). Bulletin of the Brooklyn Entomological Society 40(1945): 161-165; New York – Lancaster.