Holcocephala

Very distinctive small, “goggle eyed” robber flies sometimes known as Gnat Ogres. The head is over twice as wide as high. They forage from twig tips or the tips of other vegetation. They occur along margins of streams, fields, woods, and wet meadows and are most active from 6-10AM (Dennis, 2021).

Holcocephala calva

Thorax and abdomen grayer overall. Dark femurs. Wings evenly brownish. Abdomen strongly narrowed on proximal part.

Size: 7-9 mm

Range: Eastern U.S. north to NY

FL Range: Panhandle, North and Central Florida, though local

FL Season: April-December

Holcocephala abdominalis

Golden yellow overall. Legs yellowish with swollen hind tibiae. Wings paler distally.

Size: 4.5-7 mm

Range: Eastern U.S. and Canada

FL Range: Throughout though local

FL Season: March-December

Holcocephala fusca

Darker brown than abdominalis. Legs reddish brown with tips of tibiae, upper surface of femora (in male), and distal portions of tarsomeres blackish. Wings brown, tips grayish hyaline. (Bromley, 1951). Hind tibiae less swollen than on abdominalis. May not be separable from abdominalis and may not be a valid species. See below.

“fusca is very similar to abdominalis (they are functionally a pair of cryptic species). H. fusca was described (in a very short, two sentence paragraph!) as being distinct from abdominalis by having a general darker color. It was soon treated as a synonym of abdominalis and essentially forgotten. Recent observations show that individuals with the darker ‘fusca’ coloration also have more slender antennae and legs (1st flagellomere of antenna of abdominalis distinctly broader in middle – with a spindle-shape; fusca has a more elongate, parallel-sided flagellomere 1; hind tibia & basitarsis of abdominalis about 35% broader than hind femur, while only about 15% broader in fusca); and a slightly different aedeagus shape. So, now I am tentatively treating them as distinct spp.” -Eric Fisher

“Based on what I’ve seen working through the University of Michigan museum collection, I personally reserve abdominalis for the ones that are clearly yellow/light tan with a big ol’ swollen hind tibia. I call dingy darker brown ones with slightly swollen tibiae fusca, and throw my hands up in the air for the ones in the middle.” -Tristan McKnight, 18.ix.2014

Size: 5.5-7 mm

Range: Eastern U.S.

FL Range: Unknown, possibly erroneous

References

Bromley, S. W. (1951). Asilid notes (Diptera), with descriptions of thirty-two new species. American Museum novitates; no. 1532.

Dennis, D. S. (2021). Ethology of Holcocephala calva (Loew1872) Diptera: Asilidae) in Northeastern Florida, USA. Journal of the Entomological Research Society, 23(3), 257-277.

Pritchard, A. E. (1938). Synopsis of north and central American Holcocephala with a description of a new species (Diptera: Asilidae). Journal of the New York Entomological Society, 46(1), 11-21.