This key has been adapted from Brake (2000).
1. Vibrissa below or at the level of lower margin of eye; head in profile subquadrate; vertical diameter of eye less than 1.5x the horizontal diameter. Frons in male as wide as in female. Wing with subcostal notch seldom evident, never well-developed; R4+5 and M1 not or only slightly converging at tips; distal margin of anal cell (CuA2) usually rounded (if not, then epistoma extended dorsally, subtriangular). Abdominal tergites of male without silvery microtomentum.
- Vibrissa well above lower margin of eye; head in profile rounded ventrally, distinctly higher than long. Vertical diameter of eye usually at least 1.5x the horizontal diameter. Frons in male narrower than in female. Wing with subcostal notch usually evident, sometimes strongly so, with basal sector of C ending in an acute lappet; R4+5 and M1 sometimes converging at tips; distal margin of anal cell meeting anal vein in sharp angle. Abdominal tergites of male often with silvery microtomentum.
2. Postocellar setae cruciate or so strongly converging that the tips nearly meet. Basisternum small, without precoxal bridge. First tarsomere of hind leg often with a posteroventral comb of setae.
- Postocellar setae only slightly converging or parallel. Basisternum large and V-shaped, sometimes with a precoxal bridge. First tarsomere of hind leg without a posteroventral comb of setae.
3. C extending to R4+5 or only slightly beyond. Proboscis elongate; labella, when open, together at least twice as long as broad.
- C extending to M1. Proboscis short or elongate.
4. Lunule with one pair of setulae. Palpus usually short and clavate, but sometimes elongate. Basisternum very small and shaped like a narrow triangle. Crossvein dm-cu absent. Hind femur without a strong seta anteroventrally.
- Lunule bare. Palpus long and thin. Basisternum small and subquadrate. Crossvein dm-cu present or absent. Hind femur with a strong seta anteroventrally on distal half.
5. Crossvein dm-cu absent. Arista slender, nearly bare.
- Crossvein dm-cu present. Arista thickened at base and often densely long-haired.
6. Proboscis elongate; labella, when open, together at least twice as long as broad, each labellum with two pseudotracheae.
- Proboscis short; labella, when open, together less than twice as long as broad, each labellum with four pseudotracheae.
7. Only two lateroclinate orbital setae. Basisternum reduced to a narrow triangle. Hind femur without a strong seta anteroventrally.
- Three lateroclinate orbital setae. Basisternum small and subquadrate. Hind femur with a strong seta anteroventrally on distal half.
8. Two postpronotal setae. Bases of antennae widely separated, face with flat plate between antennae. Two or three frontal setae. Palpus enlarged.
- One postpronotal seta. Antennae approximated and not separated by a flat plate; two frontal setae. Palpus enlarged or not.
9. First flagellomere in male as large as in female. Mid femur with an anterodorsal femoral organ slightly proximal of the middle.
- First flagellomere in male usually larger than in female. Mid femur without a femoral organ.
10. Three lateroclinate orbital setae. Occiput not strongly concave when viewed from above. Palpus and first flagellomere in male usually greatly enlarged, longer than broad. A pair of usually small setae on lunule.
- Two or three lateroclinate orbital setae. Occiput strongly concave when viewed from above. Palpus not unusually enlarged; pedicel and first flagellomere subequal in length, first flagellomere broader than long, subquadrate. A pair of strong setae on lunule.
11. Frons with only one orbital seta and without interfrontal setae or hairs.
- Frons with two orbital setae and with a paired row of interfrontal setae.
12. Frons with a paired row of interfrontal setae situated on grey sclerotized interfrontal stripes; these stripes and concolorous frontal and orbital plates and ocellar triangle demarcating a dull to velvet-black M-shaped area.
- Frons without an M-shaped area.
13. Lunule extended ventrally along mid-line of face as a flat plate between the antennae, almost reaching lower margin of face; epistoma usually extended dorsally, subtriangular. Anepisternum sometimes with hairs; anepimeron with 0-2 setae. Hind tibia of male sometimes greatly broadened. Hind tibia in both sexes without tibial organ.
- Lunule not extended towards lower margin of face; epistoma not extended dorsally. Anepisternum and anepimeron bare. Hind tibia not enlarged in male. Hind tibia usually with tibial organ posteriorly in both sexes.
14. Male with all orbital and frontal setae reclinate; female with anterior orbital seta latero-proclinate, middle orbital seta latero-reclinate, posterior orbital seta absent, and frontal setae medioclinate. Wing oval; subcostal break in costa not developed into a notch. Abdominal tergites of male without silvery microtomentum.
- Male and female with anterior orbital seta usually latero-proclinate, middle orbital seta usually latero-reclinate, posterior orbital seta medio-reclinate or absent, and frontal setae medioclinate or absent. Wing triangular; subcostal break in costa developed into a notch. Abdominal tergites of male often with silvery microtomentum.
15. Frons with eight to ten pairs of uniformly arranged frontal and orbital setae, all erect and reclinate, with no distinction between orbital and frontal setae. Proboscis usually exceptionally long and slender, more than twice as long as head is high. Abdominal tergites of male without silvery microtomentum.
- Frons with orbital setae clearly distinguished from frontal setae, not uniformly arranged. Proboscis less than twice as long as head is high, usually short. Abdominal tergites of male often with silvery microtomentum.
16. Anepisternum with a row of strong setae posteriorly. Three orbital setae and usually three frontal setae, but sometimes two or up to six frontal setae.
- Anepisternum bare. Two or three orbital setae and no or two frontal setae.
17. Posterior margin of eye usually notched or emarginate, posteromedial triangular extension of tergite 1 over tergite 2 in males usually present. If both characters not present then 2 frontal setae present, posterior eye margin slowly separating from head margin ventrally and Neotropical or Nearctic distribution.
- Posterior margin of eye entire ( Milichia Meigen), posteromedial triangular extension of tergite 1 over tergite 2 in males absent.
18. Eyes more than 1.5x as high as wide. Labella, when open, together less than twice as long as broad.
- Eyes less than 1.5x as high as wide. Labella, when open, together more than twice as long as broad.
19. Usually no frontal setae in both sexes, and in some species two medioclinate frontal setae in both sexes. Anterior orbital seta in both sexes latero-proclinate, middle orbital seta latero-reclinate, and posterior orbital seta medio-reclinate if present. In some species frontal and orbital hairs enlarged so that they can be confused with the true orbital and frontal setae. R4+5 and M1 parallel.
- Female with two medioclinate frontal setae and two latero-reclinate or latero-proclinate orbital setae. Male with one anterior medioclinate and three posterior medio-reclinate frontal setae and one latero-reclinate orbital seta. R4+5 and M1 converging at tips.