Key to the Asilid Genera of the Eastern U.S.



This key was created by removing western genera from the key to the genera that appears in the 1981 Manual of Nearctic Diptera Volume 1 from the Biosystematics Research Institute, Ottawa, Ontario. The robber section was written by Grace C. Wood. This manual is now out of print. Genera that do not occur from central Texas and Oklahoma to the east were removed. So this key may be used in Oklahoma and Texas. The full key from the above Manual should be used for Kansas and anywhere west.


Some helpful images were scanned from the same article and are used only where necessary. Facial, wing and head profile shots are mostly from the Robber Flies of the World (Smithsonian, 2 volumes, 1962 -- thanks to Judy Semroc). Some additional images are from the classic C. H. Curran publication from 1934, North American Diptera. He apparently used many of S. W. Williston's original plate etchings from the earlier summary of Williston's, Manual of North American Diptera (3rd Edition, 1909).


Wings and faces are representative and may not be exact for each species. All eastern genera are included in the key. Links for terminology are to the Geller-Grimm site. Species numbers are updated from the 1981 date of the key.

And check this stunning fly anatomy site for a lesson or refresher on fly parts:


1  R 2+3 ending in C (see below)


1 R 2+3 joining R1 proximal to end of R1, with cell r1 thus separated from wing margin (below)






2  Abdominal segment 2 five or more times as long as wide. Abdominal sternite 1 either absent or extending about halfway back under tergite 2

                                                                          LEPTOGASTRINAE (see key here as well:



2 Abdominal segment 2 no more that four times as long as wide. Abdominal sternite 1 confined beneath tergite 1





3  Anal angle of wing absent; CuA unbranched; A1 absent. First flagellomere spherical, with a long slender arista arising apicodorsally. Halter as long as mesonotum




                                 Leptopteromyia Williston

(1 species in TX and FL)

3 Anal angle of wing reduced but not absent; CuA branched to form CuA1 and CuA2; A1 present. First flagellomere elongate, with arista arising apically. Halter much shorter than mesonotum

                                                  Leptogaster Meigen (now divided as below)  4




4  Middle of abdominal tergite 2 with transverse band of long hairs. Base of M2 closing cell d short, not more than 1.5 times the length of crossvein m-m; crossvein m-cu present but short, or M3 and CuA1 narrowly united with each other, the union shorter than the length of crossvien r-m



4 Abdominal tergite 2 without transverse band of hairs. Base of M2 long, twice or more the length of crossvein m-m; crossvein m-cu absent; M3 and CuA1 broadly united, the union longer than length of crossvein r-m






5  Empodia lacking. Epandrial lobe of male deeply divided, almost to base, forming narrow dorsal and wider ventral lobes. Width of face at narrowest point no wider than diameter of an adjacent eye facet



                                                                                                                               Psilonyx annulatus (Say)

(only species, Ohio to PA, south to OK, GA)


5 Empodia usually present. Epandrial lobe of male at most shallowly notched. Width of face at narrowest point 1.5-3 times as wide as diameter of an adjacent eye facet

                                                                                                      Beameromyia Martin

(5 species in the east)




6  Hind femur with distal swelling arising gradually, beginning at or before mid-length. Scutellar margin with bristles as long as crossvein r-m.

                                                                                 Apachekolos Martin

(3 species eastern, 2 Texas and 1 widespread)


6 Hind femur with distal swelling arising abruptly at about two-thirds or more the distance from the base. Scutellar margin and disc bare or with a few small hairs.





7  Flagellum 2.5 times as long as preceding two segments and one-sixth as wide as long


                                                                                                                            Tipulogaster glabrata (Wiedemann)

(only species, widespread in east)


7 Flagellum not more than twice as long as preceding two segments and one-quarter as wide as long



                                                                                          Leptogaster Meigen

(15 species in the east including Texas species)



8  One of the apical spines on the ventral side of the fore tibia differentiated, enlarged and stouter than the remaining spines, or if not noticeably larger, twisted and sigmoid


8 All the apical spines on the fore tibia straight, or if one is slightly curved, it is not thickened or sigmoid





9  Differentiated fore tibial spine stout, hooked, arising from a large basal tubercle, and opposing a group of denticles or a raised denticulate area on first tarsomere of foreleg


9 Fore tibial spine thin, sigmoid, often inconspicuous, not arising from a large basal tubercle, and not meeting a modified area on first tarsomere of foreleg





10  M3 extending to wing margin, i.e. cell m3 open. Two flagellomeres; the second one small, with an apical pit enclosing spine at apex




                                        Saropogon Loew

(12 species: 8 Texas only and 3 TX plus OK and one OK only)

See new key to genus here.


10 M3 joining CuA1 before terminating in wing margin, i.e. cell M3 closed. One flagellomere only, with pit and enclosed spine at apex




                                                             Diogmites Loew

(17 eastern species)




11 Pulvilli (flattened appendages between and opposing terminal claws of feet) present


11 Pulvilli absent





12  First flagellomere more than twice as long as scape and pedicel combined, without apical stylus, but with a small spine arising from a notch near middle of dorsal surface. Abdomen pitted.




                                                                             Taracticus octopunctatus (Say)

(only eastern species, occurring throughout)



12 First flagellomere unnotched, approximately twice as long as scape and pedicel combined, and with apical stylus; abdomen normal, not pitted





13  Male with only six visible abdominal tergites; last two tergites widened, covered with dense silvery pollen; terminalia usually hidden beneath this segment. Wing spotted, brown at crossveins and bifurcations




                                                                                            Nicocles Jaennicke

(4 species in the east; 2 east coastal, 1 TX, 1 southeast)


13 Male with seven visible abdominal tergites; last tergite not as above. Wing hyaline or basal two-thirds brown




                                                                                       Cophura Osten Sacken

(4 species, all in TX and/or OK)

See new key here.




14  Prescutal dorsocentral bristles lacking, although scutum usually with short appressed scale-like white hairs; pedicel with a long, strong bristle




                           Hodophylax aridus James

(Texas, Kansas only)

14 Long prescutal dorsocentral bristles present; pedicel without bristles




                 Parataracticus melanderi Wilcox

(TX only in the east)



15 Frons greatly expanded toward vertex; vertex, measured from above eyes, at least 1.7 times as wide as face at level of antennae



15 Sides of frons usually more or less parallel or converging toward vertex, but if expanded only slightly so





16  Face strongly inflated on lower three-fourths, with hair of mystax on lower half or more




                                                                        Lasiopogon Loew

(14 species in the east, many newly defined, see here)


16 Face plane or slightly convex, with mystax confined to its lower margin





17  M3 absent beyond cell d. Mystax sparse, consisting of five or six pairs of widely spaced slender bristles in a transverse row




                                  Townsendia Williston

(3 species, 1 FL, 1 TX, 1 extensive)


17 M3 present from cell d to wing margin. Mystax dense, consisting of six to twelve pairs of straight moderately stout bristles



                                                                                          Stichopogon Loew

(5 species, 2 extensive, 1 northeast, 1 TX, 1 TX, AR, OK)




18 Head very narrow, as high as wide, appearing more or less circular in frontal view




                                          Stenopogon Loew (now divided as below)  19

18 Head wider than high





19   Katatergite (see 16 here) without hairs or bristles. Requires lens to see

                 Stenopogon Loew

(Large western genus. Only 1 species reaches Texas: inquinatus Loew) 

19  Katatergite (see 16 here) with hairs, bristles or both. Requires lens to see





20  First flagellomere less than 1.75 times the combined length of scape and pedicel; scape 1-1.5 times length of pedicel. second and third flagellomere forming an apically pointed stylus, with a short spine at apex. Wing hyaline.

                                                           Scleropogon Loew

(9 species in the east, 6 reach only Texas, 1 OK and TX,

1 is confined to FL and 1, subulatus (Wiedemann), is widespread)

20 First flagellomere two or more times combined length of scape and pedicel; scape twice or more as long as pedicel; second and third flagellomeres absent. Wing usually brown.




                                                        Ospriocerus Loew

(13 species reach Texas and several to OK, none known farther east)

(See new key to this genus here.)




21  Apical portion of M3 in line or nearly so with crossvein m-m. Very large flies, 35-50 mm long




                                                                                         Microstylum Macquart

(2 species in Texas, morosum Loew now found in OK, AR as well)

21 Apical portion of M3 at an angle to crossvein m-m. Smaller flies, less than 28 mm long





22  Apex of R2+3 directed sharply forward meeting C at an angle of about 90 degrees, ending either at distal end of R1 (cell R1 closed) or a short distance along C (cell R1 open); R4 strongly sinuate and arched forward after separation from R5. Male with only six abdominal tergites visible dorsally


                               LAPHYSTIINI    23

22 Apex of R2+3 not directed sharply forward before ending in C; R4 not usually arched and sinuate. Male with seven or eight tergites visible dorsally





23  R5 and M1 each ending separately in wing margin, thus cell R5 open, rarely closed. All abdominal tergites with bristles



23 M1 ending in R5, thus cell R5 closed. Third and succeeding abdominal tergites without bristles



                                                                  Zabrops Hull

(one species, flavipilis (Jones) to AR, MO, IA and OH)




24  Face wide, about width of eye. Antennae with stylus. Scutellum without bristles




                                                                                                 Laphystia Loew


24 Face narrower, two-thirds width of eye. Antennae without stylus. Scutellum with at least one pair of bristles




                                                                                               Psilocurus Loew

(7 species which all occur in TX, 2 spread somewhat eastward, see link page for other info)




25  Face with pronounced tentorial pits or grooves extending well above lower facial margin; face not produced beyond eye margin. Eye large, rounded, making head width 1.7-2.0 times head height. Abdomen very short, usually three-quarters or less of wing.



25 Face without pronounced tentorial pits or face produced beyond eye margin in profile. Head narrower, its width less than 1.7 times height. Abdomen longer than three quarters of wing length.





26  Face with pronounced transverse groove about one-fourth distance between lower facial margin and antennae (see above face); face with four to six bristles along lower margin and a few fine reclinate hairs in middle




   Holcocephala Jaennicke

(3 species, all three widespread)


26 Face without transverse groove; face with pale proclinate bristles or hairs on lower two-thirds




                                             Haplopogon Engel

(3 species, TX only)




27  Lower margin of face wider than eye. Face and frons converging strongly to vertex




                    Plesiomma Macquart

(1 US species, unicolor Loew, in TX and NM)

27 Face and frons not strongly converging dorsally





28  Face haired over lower one-third or less; upper two-thirds of face bare, or with a tuft of hairs at antennal base separated from mystax by a bare area, or with a row of weak hairs along eye margin. Abdominal tergite 10 of female without strong bristles

                    DIOCTRIINI     29

28 Mystax occupying lower half or more of face, but without separate tuft or row of hairs. Abdominal tergite 10 of female with strong bristles





29  Hind femur and hind tibia each club shaped. R4 ending posterior to wing tip

                    Nannodioctria Wilcox & Martin

(1 Florida species: seminole (Bromley))

29 Hind femur thickest subbasally, at middle, or only gradually enlarged apically. R4 ending anterior to wing tip





30  Scutellar margin with moderately long erect hair, as long as scutellum; disc of scutellum with appressed short hair.




                    Echthodopa Loew

(3 species, 1 TX and west only)


30 Scutellar margin without long hair; disc of scutellum bare or with minute hairs




                                                                                                                                      Eudioctria Wilcox & Martin

(5 eastern species)




31  Pulvilli lacking. Thorax, legs, pronotum and base of C with appressed scale-like hairs



                    Ablautus Loew

(1 of the western species, rufotibialis Back, reaches TX)

31 Pulvilli present. Body, legs and wing without scale-like hairs





32  Stylus absent; first flagellomere very long, about three times combined length of scape and pedicel, with apical pit and spine. Cell m3 closed or occasionally narrowly open at wing margin; wing dark brown




                    Prolepsis tristis (Walker)

32 Stylus present; first flagellomere shorter. Cell m3 open to margin, usually wide open, wing hyaline





33  Antennae with three flagellomeres; flagellomeres elongate, not stylus-like; second and third flagellomeres as wide as or wider than first. Face in profile produced beyond eye margin, with antennal bases on raised area




                    Ceraturgus Wiedemann

(10 US species, all eastern, all uncommon)


33 Second flagellomere of antennae stylus-like, narrowing apically, often with a spine. Face sometimes produced, but antennal bases never on raised area





34  Wing with brown spots at crossvein r-m, at bifurcation or R4 and R5, and at apex of cell d




                    Metapogon Coquillett

(1 western species, punctipennis Coquillett, reaches TX)


34 Wing hyaline or infuscated, or if spots present not in the three positions shown





35  Face strongly convex




                    Cyrtopogon Loew

(Huge western genus with about 11 species occurring

in the east, some in the northeast and Maine area only)

35 Face flat, slightly raised beyond eye margin





36  Hind tibia much enlarged, as thick as or thicker than hind femur. CuA2 and A1 joined before wing margin (see labeled wing above)



                    Holopogon Loew

(6 eastern species, several widespread)

36 Hind tibia thinner than hind femur. CuA2 and A1 ending separately in wing margin





37  Dorsal 2/3 of face with four to six pairs of bristles perfectly aligned in two neat parallel, vertical rows (see below micrograph). Genitalia conspicuously enlarged and angled forward beneath abdomen.



                    Hadrokolos Martin

(3 species, OK and TX only)

37 Mystax sparse or dense, but without two rows of bristles parallel. Genitalia neither enlarged or angled forward.





38  Hairs plumose (visible at 25X) on pronotum, upper occiput, and side of thorax. Frons with tufts of hair laterally




                    Heteropogon Loew

(7 eastern species, 5 confined to TX or OK in east)

38 Hairs straight or crinkly, not plumose. Frons with a lateral row of fine hairs





39  Face in profile nearly flat. Scutum humped. Legs and dorsum of abdomen with green or blue metallic reflections

                    Sintoria Hull

(1 TX species, pappi Wilcox)


39 Face in profile flat or slightly convex. Scutum not humped. Metallic reflections absent



                                                                                                                                      Wilcoxia James

(1 TX species, pollinosa Wilcox)



40  Antennae blunt apically, without stylus, or with one or two abruptly tapered short microsegments. Palpus two-segmented. Crossvein m-cu present; thus apex of cell bm closed by three veins


40 Apex of antenna with long slender bristle-like stylus. Palpus one-segmented. Crossvein m-cu absent, and veins M3 and CuA1 joined together; thus apex of cell bm usually closed by only two veins, except in Mallophora and some Efferia





41  Postmetacoxal region with a transverse heavily sclerotized bridge. First flagellomere either with a short bristle arising near middle of dorsal surface, or with a stylus at apex

                    ATOMOSIINI and Dasylechia   42

41 Postmetacoxal area membranous. First flagellomere without a stylus, but with an apical pit containing a short spine or bristle

                                                                                                                                      LAPHRIINI except Dasylechia   44




42  Species resembling bumblebees, more than 2.5 cm long, with entire face and body densely haired. Anatergite (see 18 here) bare; sclerotized part of postmetacoxal region very narrow, with its posterodorsal margin U-shaped




                    Dasylechia Williston

(1 species, scattered eastern records, very rare)


42 Small rather bare species, less than 20 mm long, often with punctate mesonotum and abdomen. Anatergite (see 18 here) with bristly pile; sclerotized part of postmetacoxal region more extensive, with it posterodorsal margin V-shaped





43  Lateral margins of frons curved, converging at vertex




                    Atomosia Macquart

(About 9 species, all eastern)

43 Lateral margins of frons straighter, diverging at vertex




                                                                                                                                      Cerotainia Schiner

(2 species, both widespread in east)




44  Proboscis laterally compressed, two or more times as wide in profile as when viewed from above


44 Proboscis either more or less cylindrical, or dorsoventrally compressed, narrower in profile than when viewed from above





45  Hind femur with tubercles on ventral surface




                    Lampria Macquart

(2 species, both eastern and widespread)

45 Hind femur without tubercles



                                                                                                                                      Laphria Meigen

(Huge genus, with at least 33 species in the east. Key here does

not include all eastern species. Genus is under revision.)




46  Proboscis more or less cylindrical, blunt at tip. Basal portion of M2 that closes cell d parallel with apical portion of M3 almost forming a straight line




                    Orthogonis Hermann

(1 species stygia (Bromley), rare, see link)

46 Proboscis dorsoventrally compressed, boat-shaped and pointed at end in profile. Basal potion of M2 and apical portion of M3 not parallel and not forming a straight line





47  Hind margin of wing membranous, C ending proximal to wing tip, slightly beyond apex of R4. Upper half of face with appressed pile. Ocellar bristles shorter than flagellomere. Lateral margins of abdominal tergites with very short inconspicuous pile; abdomen short, wide





                    Cerotainiops Curran

(2 species reach OK and TX)


47 Hind margin of wing thickened, continuous with C. Face with strong erect bristles, at least on lower half. Ocellar bristles as long as or longer than flagellomere. Lateral margins of at least abdominal tergites 1 and 2 with long conspicous pile






48  R2+3 and R4 connected by a short extra crossvein




                    Pogonosoma Rondani

(2 species, 1 extensive and one TX, MI, ME)

48 R2+3 and R4 not connected by such a vein




                                                                                                                                      Andrenosoma Rondani

(5 species, 1 FL, 3 TX and 1 widespread)



49  Antennal stylus plumose. Postmetacoxal area heavily sclerotized



                    Ommatius Wiedemann

(7 eastern species)

49 Antennal stylus bare

                                                                                                                                      ASILINI    50




50  Anatergite (18 here) bare


50 Anatergite pilose





51  R4 with a recurrent vein arising near its junction with R5; recurrent branch sometimes short, ending in cell R2+3,


 or sometimes extending toward base of wing until it joins R2+3




51 R4 without an extra vein







52  Apical half of R5 subparallel to R4, usually meeting C before wing apex except in aestuans group. Posterior basalare (number 9 here) bare




                    Efferia Coquillett

(Largest genus in North America, but limited

to about 7 species east of TX. TX has 45)

52 Apical half of R5 diverging strongly from R4, meeting C well behind wing apex. Posterior basalare haired






53  Claws acute




Promachus Loew

(About 16 species in the east, again TX dominant)

53 Claws blunt






54  Abdomen slender, as long as or longer than wing. Male terminalia relatively large, about as wide as abdominal tergite 7, and longer than wide




                    Amblyonychus Hermann

(1 species in TX, trapezoidalis (Bellardi))

54 Abdomen broad, shorter than wing. Male terminalia small, narrower than abdominal tergite 7, and wider than long






55  Lower half of face prominently bulging; upper half almost bare, shining. Hind femur long, club-shaped, with row of bristles on anterior surface




                    Mallophora Macquart

(5 species, 1 FL, 2 TX, 1 southeast and 1 widespread)

55 Lower half of face more evenly convex, with pile on upper half. Hind femur thickened in middle, spindle-shaped, without row of bristles on anterior surfaces




                                                                                                                                      Megaphorus Bigot

(about 8 eastern species)




56  R5 reaching wing margin anterior to wing tip



56 R5 reaching wing margin posterior to wing tip





57  Abdomen long and slender, tapering, much longer than wing; lateral margins of abdominal tergites 1 and 2 with sparse short pile. Lower three-quarters of face swollen. Species not resembling bumblebees



Female genitalia



                    Proctacanthus Bromley

(13 eastern species)

57 Abdomen short and wide, no longer than wing. Lateral margins of abdominal tergites 1-3 with abundant long pile. Lower one-half of face swollen. Bumblebee mimics



                                                                                                                                      Eccritosia Schiner

(1 species reaching TX, zamon (Townsend))




58  Lower part of face only moderately swollen; face five-sevenths as wide as one eye. Male with large hypandrium as long as or longer than sternite 7. Female with spines on cercus. Scutellum swollen, without groove near margin




                    Proctacanthella Bromley

(5 species in the east)

58 Lower part of face strongly swollen; face narrow, three-eights as wide as one eye. Male with small hypandrium. Female without spines on cercus. Scutellum with groove near margin

                                                                                                                                 Asilus Linnaeus; Machimus Loew (image below); Dicropaltum Martin;




Neomochtherus Osten Sacken

(Large group with most of the species in east now

included in Machimus. 2 Dicropaltum species.

1 Asilus. 4 Neomochtherus.

Polacantha gracilis)



59  Occipital bristles long, fine; distal one-third strongly proclinate. Abdominal segment 6 of female incorporated into terminalia




                    Neoitamus Osten Sacken

(2 eastern species)


59 Occipital bristles not proclinate at apices, or if slightly so, less than apical one-fourth curved. Abdominal segment 6 of female not incorporated into terminalia


Asilus Linnaeus;





Machimus Loew;

Dicropaltum Martin; Neomochtherus Osten Sacken;




Philonicus Loew

(Large group with most of the species in east now

included in Machimus. 2 Dicropaltum species.

1 Asilus. 4 Neomochtherus. 2 Philonicus.)