These small, hump-backed flies are often found in deep shade. The genus is unique in having feathered antennae. There are four species recorded in Florida. However, O. floridensis was first described in 1984 and is very similar to O. tibialis. I suspect most museum records for O. tibialis in Florida are actually O. floridensis, and O. tibialis is restricted to the panhandle “highlands.”
Let’s start off with the easy one. O. wilcoxi has dark reddish-yellow legs (femora and tibias) and dusky wings. Black on the femora is restricted to the tips.
Size: 13-17 mm
Season: May – August
FL Range: Panhandle and north Florida south to Gainesville
The legs are pale yellowish, transitioning to black. The rear femora are about one-third black. The presence of two long bristles on the rear of the scutellum (bump above the wings), differentiated from any other hairs on the scutellum, is distinctive in O. gemma. Also note the small size. When viewed laterally, the epandrium (upper male genitalia) has a very thin projection, making it appear strongly pointed. The hypandrium (bottom of male genitalia) is rounded.
The ventral margin of female abdominal segment 8 is broadly rounded and has a short point in the middle. This can only be seen on a specimen.
Size: Small. 9-13 mm
Season: February – November
FL Range: Throughout
Both O. floridensis and O. tibialis have orange and black legs. The shape of the end of the male genitalia (epandrium) separates O. floridensis from O. tibialis. When viewed laterally, the epandrium (upper male genitalia) has a more pointed projection on O. floridensis; it’s more rounded in O. tibialis. The hypandrium (bottom of male genitalia) has a knob, which is lacking in O. tibialis. Both O. floridensis and O. tibialis have no clearly differentiated vertical bristles on the scutellum (bump above the wings) like O. gemma has.
The W- or U-shape of the posterior ventral margin of abdominal segment 8 is important in the females. It’s a shallow W in O. floridensis and a deeper W in O. tibialis. You need a specimen to see this, though I would be keen to see if anyone can get an in-situ macro shot of the underside of one.
Size: 14-16 mm
Season: March – December
FL Range: Throughout
When viewed laterally, the hypandrium (bottom of male genitalia) has no knob like O. floridensis. Legs are orange and black, possibly with more black on femurs on average than on O. floridensis. No long bristles on scutellum (bump above wings).
Size: 13-16 mm
Season: June – September throughout eastern range
FL Range: Panhandle. Bullington and Lavigne (1984) lists one Florida record from Liberty County.
Diagrams from Bullington & Lavigne (1984)
Bullington, S. W., & Lavigne, R. J. (1984). Review of the genus Ommatius Wiedemann (Diptera: Asilidae) in eastern United States with descriptions of five new species. Annals of the Entomological Society of America, 77(4), 372-392.
Scarbrough, A. G. (2008). New Ommatius Wiedemann from the Americas with two new species groups, keys, and taxonomic notes (Diptera: Asilidae). Insecta Mundi, 151.