Leptogastrinae

The diagnostic character for this group is that the first abdominal segment is five or more times as long as wide, giving these a slender appearance. These are small and inconspicuous. Whereas many robber flies are ambush predators, flying out to attack nearby prey, several species in this subfamily hover slowly and attack stationary prey items on vegetation, similar to how damselflies hunt. They will take spiders from webs. Most museum specimens for this group were collected passively with malaise traps. Encountering one of these small flies in life is always exciting.

Geller-Grimm’s pictoral key to the genera in this group is here. The genera include Apachekolos, Beameromyia, Leptogaster, Leptopteromyia, Psilonyx, and Tipulogaster. The available keys are based on male genitalia and sometimes antennae, so I have tried to highlight other features. A table comparing features for all Florida species is at the bottom of this page. Note that several photos on my page are specimens from FSCA, and I have assumed the species determinations by J. Wilcox and L.G. Bezark are correct. They appear to be.

Apachekolos tenuipes

Legs are long and slender. Hind femora with distal swelling arising gradually, starting at or before mid-length. Mostly black with some red on thorax. A diagnostic feature separating this genus from other Leptogastrinae is the lack of a transverse band of hairs on abdominal segment 2, but this can be hard to see on photos. If viewing male genitalia with a scope, note that the epandrial lobe is deeply divided almost to the base, with the ventral branch subequal in length to and narrower than the dorsal branch (Artigas and Papavero, 1988).

Size: 9-10 mm

Range: Southeastern U.S.

FL Range: Alachua, Marion, and Orange Counties

FL Season: May, August, October

Beameromyia chrysops

Yellow legs. Black thorax. Dark abdomen with reddish yellow bands.

Size: 7 mm

Range: Florida, Georgia, Alabama

FL Range: Throughout (Monroe, Palm Beach, Gadsden, Leon Counties).

FL Season: May-July

Beameromyia disfascia

The thorax is black with white (pollinose) on the sides. The abdomen is black with white posterior bands on segments 2, 3, and 4, and a white posterior corner of segment 5. Legs yellow, with the four forelimbs darkened dorsally. Hind femora and tibiae with reddish brown band on swollen portion. Head black. Face white tomentose (dense tiny hairs, making it appear uniformly white). Vertex and upper occiput brown. Six pale mystax (face beard) bristles. Proximal antennal segments, third segment, and style of equal length, orange-red in color, third and style reddish brown. Third with two short stout bristles near apices. Gonoforceps with sharply angulate ventral margin.

Size: 7 mm

Range: Eastern U.S.

FL Range: Throughout, but based on sparse records (Alachua, Liberty, Monroe Counties)

FL Season: February-October

Beameromyia floridensis

Similar to B. pictipes, but broad apical band on hind femora, and broad band on swollen hind tibiae. Thorax light brown with dark brown stripes. Abdomen black with pale/orange bands. Gonoforceps expanded apically, with prominent notch (Martin, 1957).

Size: 7-9 mm

Range: Virginia to Florida, Puerto Rico

FL Range: Throughout, but based on sparse records (Alachua, Highlands, Leon, Miami-Dade, Monroe Counties)

FL Season: All year

Beameromyia pictipes

Thorax polished black. Thin white bloom on thorax, light brown bloom on scutum. Female abdomen very swollen like Psilonyx annulatus. Abdomen dark brown and polished. Gradual swelling on hind tibia. Hind tibia with median yellow ring (basally tibia only darkened in some specimens, yellow ring not sharp). Gonoforceps truncate apically. Closely resembling Psilonyx annulatus, but P. annulatus has striking bands on tibia and empodia are lacking.

Size: 5-7 mm

Range: Eastern and mid-western U.S.

FL Range: Unknown

FL Season: Unknown

Beameromyia vulgaris

Hind tibia orange apically (at the tip) with a dark reddish brown band on the swollen portion. In some specimens, the tip is darkened and on some the band is indistinct. Black thorax. Banded abdomen.

Size: 5-7 mm

Range: Eastern U.S.

FL Range: Throughout but based on sparse records (Alachua, Highlands, Monroe Counties)

FL Season: January-October

Leptogaster aegra

Larger than atridorsalis. Reddish, polished scutum. Antennal segments yellow. Abdomenal segments 3 to 4 dark dorsally, yellow laterally. Segments 5 to 8 dark reddish brown, subshining. Legs pale, hind femora and tibiae darkened apically. Gradual swelling of hind femora.

Size: 11-16 mm

Range: Southeastern U.S.

FL Range: Throughout south to Manatee and Highlands Counties

FL Season: March-October

Leptogaster atridorsalis

Polished black scutum (top of thorax). Abdomen polished black with yellow posterior margins. Gradual swelling on hind femora with yellow band. Third antennal segment black.

Size: 8-10 mm

Range: Eastern U.S.

FL Range: Panhandle and North Florida (Alachua and Jackson Counties)

FL Season: April, July, August, December?

Leptogaster brevicornis

Scutum (top of thorax) brown with obscure stripes. Abdomen with yellow orange rings. Hind tibia brownish with median yellow ring. Hind femurs with dark brown ring. Yellow antennae. Empodium (bristle-like or pad-like structures between the tarsal claws,) short, about one-half length of tarsal claws. Gonoforceps (male genitalia structure) not divided. Three pairs of penis valves, with median process just below valves. Sternite 9 smooth basally. Sternite 1 narrow or triangular. Sternite 2 narrow. Both fused to tergite 2 (Martin, 1957).

Size: 8-12 mm

Range: Southeastern U.S.

FL Range: Throughout but based on sparse records (Liberty, Monroe Counties)

FL Season: May-July

Photo by Paul Bedell

Leptogaster flavipes

Antennae and legs normally yellow. Thorax and abdomen gray laterally to brown pollinose dorsally. Ground color of abdominal segments 2 to 4 dark with posterior yellow or reddish bands. Sternite 9 subdivided into divisions by more or less distinct lines. Gonoforceps pointed apically.

Size: 8-13 mm

Range: Eastern U.S. and Canada

FL Range: Panhandle and North Florida

FL Season: April-May

Leptogaster lerneri

Hind femora and tibiae each with broad brown bands. Thorax reddish or reddish yellow, somewhat striped. Mystax white. Dorsal arm of gonoforceps curves U-like. Elongate ventral spur connected with dorsal arm. Wings with brown veins.

Size: 8-9 mm

Range: Florida Keys and Bahamas

FL Range: South Florida (Monroe County), including Long Key and Dry Tortugas

FL Season: April-September

Leptogaster obscuripennis

Legs almost entirely reddish yellow. Swollen hind femora with an orange band in some individuals. Thorax reddish or brown and shining. Abdomen yellow brown with black terminal segments. Brown wings. Dark hair on thorax is sparse and not as erect as on obscuripes. Length of third antennal segment about equal to two basal segments. Dorsum of thorax with dark, more erect hair. Found in sandhill habitat.

Size: 12-14 mm

Range: Southeastern U.S.

FL Range: Throughout

FL Season: April-December

Leptogaster obscuripes

Dark reddish to black, shining, on both scutum and abdomen. Anterior legs with dark dorsal stripe. Length of third antennal segment about equal to two basal segments. Clear wings.

Size: 17 mm

Range: Florida, Texas, Cuba

FL Range: Monroe County

FL Season: March, October?

Leptogaster virgata

Three shining black stripes on thorax. Empodium shorter than tarsal claws. Epandrium with deep cleft. Martin (1957) did not study the types for L. carolinensis, which supposedly occurs in NC and SC, and considered it synonymous with L. virgata after Back (1909)’s suggestion.

Size: 9-13 mm

Range: Eastern U.S. (NY to Georgia, west to Oklahoma and Texas)

Leptogaster murina

Scutum brown tomentose (not polished). Lateral margins of abdomen are gray, and dorsum is brown. Abdomen not polished. Legs mostly unmarked. Apical half of hind tibia brown; basal half yellow. Found in prairies and tall grasses.

Size: 12-15 mm

Range: Midwest east to Ohio, Arkansas, Louisiana. Scarbrough and Kuhar (1992) identified several specimens from Maryland.

Leptogaster incisuralis

Scutum black dorsally, reddish laterally. Abdomen with dark bands around incisures and orange between bands. Almost identical color patterns to L. flavipes. Usually L. incisularis has more red ground color laterally on scutum, whereas the scutum of L. flavipes is entirely black. Male gonoforceps more truncate than L. flavipes.

Size: 10-13 mm

Range: Eastern U.S. and Canada south to Georgia. There are numerous specimens in the UCF collection from central Florida labeled as L. incisuralis, but they may be misidentified.

Leptopteromyia americana

Halter as long as mesonotum. These are extremely small and slender. Reddish brown scutum. Yellow rings on dark abdomen.

These lay their eggs in the silken galleries of webspinners (Embioptera) (Cohen, 2014).

Size: 6-9 mm

Range: Florida, Texas, California

FL Range: Peninsular Florida (Alachua, Brevard, Highlands, Orange, Polk, Seminole, Sumter Counties)

FL Season: All year

Psilonyx annulatus

Striking color markings on the legs. Swollen hind femora is brown with red or orange band. Hind tibiae have three dark bands and two pale bands: Dark, white, dark, orange, dark. The lack of empodia, which are bristle-like or pad-like structures between the tarsal claws, distinguishes this genus. Transverse band of long hairs on middle of abdominal segment 2. “Epandrial lobe of male deeply divided, almost to base, forming narrow dorsal and wider ventral lobes.” (Artigas and Papavero, 1988)

Size: 8-11 mm

Range: Eastern U.S. and Canada

FL Range: Throughout

FL Season: All year

Tipulogaster glabrata

Reddish brown, polished. Hind femora yellowish-brown with a thin brown ring. The banding on the abdomen, when visible, is because of a slightly paler shade of orange on the posterior edges of each segment. No transverse band of hairs on abdominal segment 2.

Size: 12-15 mm

Range: Eastern U.S. and Canada

FL Range: South to Highlands County

FL Season: March-August (one November record)

Feature comparison

Species	Size (mm)	Front leg color	Swollen hind femora	Hind femora color	Hind tibiae	Scutum	Abdomen
Apachekolos tenuipes	9-10	Black and red	Gradual swelling	Black outside, reddish inside. No band.	Black outside, reddish inside	Black with some red	Brown then black towards apex
Beameromyia chrysops	7	Yellow orange	Yes	Yellow orange. No band.	Yellow orange	Black	Dark with reddish yellow bands
Beameromyia disfascia	7	Yellow, darkened dorsally	Yes	Yellow. Swollen portion dark with prominent orange band.	Dark then reddish brown on apex	Black	Black with white bands on sides
Beameromyia floridensis	7-9	Yellow	Yes	Yellow. Swollen portion dark with broad orange band.	Broad orange band	Light brown with dark brown stripes	Black with pale/orange bands
Beameromyia pictipes	5-7	Whitish	Gradual swelling	Brown with median yellow or reddish brown ring	Brown with reddish tip	Black, polished, with obscure stripes	Dark brown, polished
Beameromyia vulgaris	5-7	Yellow	Yes	Reddish brown band	Dark then reddish brown on apex	Black	Dark, pale banded
Leptogaster aegra	11-16	Reddish yellow	Somewhat	Reddish yellow	Reddish yellow	Reddish, polished	Dark dorsally, yellow laterally
Leptogaster atridorsalis	8-10	Yellow	Gradual swelling	Brown with yellow band	Yellow with dark apical half	Black, polished	Polished black, yellow posterior margins (bands)
Leptogaster brevicornis	8-12	Yellowish	Somewhat	Brownish, median yellow ring	Dark brown ring	Brown with obscure stripes	Yellow orange rings
Leptogaster flavipes	12	Yellow	No	Yellow with dark tips	Yellow with dark tips	Pale brown with pale gray stripes	Gray with posterior yellow or reddish bands
Leptogaster lerneri	8-9	Brown with reddish apices	Yes	Yellow to reddish with broad brown bands	Yellow to reddish	Reddish, somewhat striped	Brownish with some red on sides of first few segments
Leptogaster obscuripennis	12-14	Reddish yellow	No	Reddish yellow	Reddish yellow	Reddish or brown, shining	Yellow brown with black terminal segments
Leptogaster obscuripes	17	Reddish yellow with dark dorsal stripe	No	Reddish with pale band	Reddish	Dark reddish to black, shining	Black, shining
Leptopteromyia americana	6-9	Yellow	Yes	Yellow with brown or red on swollen portion.	Yellow then brown	Reddish brown, white on lateral and hind margins	Yellow rings
Psilonyx annulatus	8-11	Yellow with dark tips	Yes	Yellow then brown on swollen portion with red or orange band.	Three black bands, two pale bands: Dark, white, dark, orange, dark	Brown or pink with pale brown stripes	Dark (darker on males) with pale bands. Terminal segments mostly pale on sides.
Tipulogaster glabrata	15-17	Orange	No	Yellow to orange with thin brown ring	Yellow to orange	Red or orange, shining	Orange with black dorsum, faintly banded (moreso on males)

References:

Artigas, J.N. & Papavero, N. (1988): The American genera of Asilidae (Diptera): Keys for identification with an atlas of female spermatecae and other morphological details. I.Key to the subfamilies and subfamily Leptogastrinae. – Gayana. Zoologia. Universidad de Concepcion, Instituto Central de Biologia 52(1-2): 95-114; Concepcion.

Back, E. A. (1909). The robber-flies of America, north of Mexico, belonging to the subfamilies Leptogastrinae and Dasypogoninae. Transactions of the American Entomological Society (1890-), 35(2/3), 137-400.

Cohen, C. (2014). Taxonomic revision of the robber-fly genus Leptopteromyia Williston, 1907 [poster presentation]. 2014 ESA Annual Meeting.

Curran, C. H., Cazier, M. A., Rindge, F. H., Vaurie, C., & Vaurie, P. (1953). The Asilidae and Mydaidae of the Bimini Islands, Bahamas, British West Indies (Diptera). American Museum novitates; no. 1644.

Hardy, D. E. (1947). The Genus Leptopteromyia (Asilidae-Diptera). Journal of the Kansas Entomological Society, 20(2), 72-75.

Johnson, C. W. (1913). Insects of Florida. 1, Diptera. Bulletin of the AMNH; v. 32, article 3.

Martin, C. H. (1957). A revision of the Leptogastrinae in the United States (Diptera, Asilidae). Bulletin of the AMNH; v. 111, article 5.

Martin, C. H., Hayden, E. B., Giovannoli, L., & Rabb, G. B. (1957). The Asilidae of the Bahama Islands, with the description of two new species. American Museum novitates; no. 1847.

Scarbrough, A. G., & Kuhar, T. P. (1992). Biodiversity of robber flies in Maryland and Delaware: Part I. Subfamily Leptogastrinae. Maryland Naturalist, 36, 13-38.

Scarbrough, A. G. (1996). The genus Leptogaster (Diptera: Asilidae) from the West Indies. Entomological News, 107(4), 193-206.