If you thought Efferia were tricky, prepare to be demoralized by Machimus. Machimus are similar to Efferia, though they are browner and do not have the swollen male genitalia nor swordlike ovipositors. Also compare other genera in the Asilinae subfamly: Neoitamus, Philonicus, and Polacantha.
Machimus are very difficult to ID. The coloration on the femurs and tibias and the leg hair color are important. Seasonality is also important, with most species either having a spring or fall flight season. Greatest diversity is in the panhandle and north Florida. Only the range of M. floridensis and hubbelli includes south Florida, and both of those are Florida endemics.
The best way to distinguish males of several Machimus species is by genital shape, especially that of the proctiger, a structure between the epandrium halves. Specimens are needed to see this. I have organized the species accounts below based on femur color. Note there is a difference between an entirely black femur and a black femur with a small red tip. Though there are exceptions, the color of the femora, tibiae, metatarsi, leg hairs, and mystax (face beard) can usually get you most of the way toward an ID.
Mostly red femora
|fattigi||23-26 mm||whitish||Mostly red with minor black spots||red||red||bristles black|
|polyphemi||11-18 mm||golden yellow||Reddish yellow with black in middle portion of anterior surfaces||reddish yellow basally||reddish yellow with black tips|
Red femora, tibiae, and metatarsi. White mystax (face beard).
Size: Large. 23 to 26 mm
FL Season: May – June
FL Range: Panhandle
This species is found either within or very close to gopher tortoise burrows. Bullington & Beck (1991) hypothesized that this species (and two western sister species which occur in Badger burrows) retreated to burrows to find a favorable microclimate as the climate changed. Once they became completely adapted to burrows, they may have been able to fully realize this niche and spread to a larger geographic area than their original distribution. A great writeup on survey methods for this species can be found here.
A very golden yellow species overall, with extensive reddish on femora and tibiae. Golden yellow mystax.
Size: 11-18 mm
FL Season: May to July
Range: MS, GA, FL
FL Range: Recorded in panhandle and north Florida (Santa Rosa, Putnam Counties in Bullington & Beck, 1991; and Alachua, Hamilton, Gadsden, and Liberty counties based on an ongoing survey led by Jonathan Mays). It may occur throughout the state where there are Gopher Tortoises.
Black femora and tibiae
|maneei||10-12 mm||gray and black hairs||Shining black||black, sometimes with trace of reddish at base of tibia||femora with some white hair and black bristles|
Mostly-black, entirely black legs. There can be a trace of red at the base of each tibia in some specimens, and there can be reddish hairs on the inside of the rear tibiae and tarsi.
Size: Small. 10-12 mm
Season: April – November throughout range. Dirk Stephenson has found these are downright common in October and November in good habitat in Georgia. There is a Florida October record at FSCA.
Range: Eastern U.S. and Canada, north to Ontario, west to Illinois and Arkansas.
FL Range: Gainesville
Habitat: Turkey oak sandhills and likely other sandy pinewoods.
Excellent photo of a male by Brad Moon.
Brown femora and tibiae
|hubbelli||11-15 mm||white with some black bristles||Brown, though black on anterior aspects||Brown to black||Black bristles, white hairs|
Similar to M. maneei, but legs and hypopygium brown instead of black.
Size: 11-15 mm
FL Season: September – December
FL Range: Clay County to Highlands County. Florida endemic.
Entirely black femora
|frosti||12-14 mm||black above, pale below||black||red with black tips||underside of front femora with long fine pile as in M. snowii. black bristles and pale hairs|
|notatus||14-18 mm||dark||black||red on basal third|
|novaescotiae||14-18 mm||black above, yellowish below. Sometimes entirely light.||black||yellow with black tips||mostly yellow|
|sadyates||13-17 mm||dark upper mystax||black||one side black, one side yellowish or reddish|
Entirely black femora, mostly red tibiae, mystax black above and pale below, found in Spring. Underside of front femora with long hairs. Wingtips pale brown. Third antennae segment narrow and same length as arista (antennae tip). Male genitalia similar in form to M. virginicus.
Size: 12-14 mm
FL Season: March – May
FL Range: North and Central Florida
Black femora, and mostly black tibiae with red only on the basal third. Dark mystax and face.
Size: 14-18 mm
FL Season: April, May, July
FL Range: Gainesville and Jackson County (panhandle)
All black femora. Tibiae yellow (or orange) with black tips. Metatarsi mostly yellow. Mystax black above, yellowish below. Somestimes the mystax is entirely light-colored. Occipital bristles mostly black above and yellowish at sides. Penultimate abdominal tergite on the female tomentose. Third antennae segment narrow and same length as arista (antennae tip). Male forceps (on genitalia) supposedly as long as abdominal segments 6-8.
Size: 14-18 mm
FL Season: April – May
FL Range: Panhandle and North Florida
All black femora. Dark legged. Dark upper mystax. Penultimate abdominal tergite on the female shiny black. Note that one side of each tibia is yellowish or reddish, and one side is black.
Size: 13-17 mm
Season: July – November
FL Range: There are Citrus and Hillsborough County records in the FSCA collection, though these are likely erroneous, especially since one is marked as March. This species likely does not occur in Florida. It’s predominantly a northeastern species.
Dark femora with reddish tip
|blantoni||16-21 mm||yellow with some black hairs||dark with reddish tip||reddish, extreme tips black||reddish with black tips||long fine white pile under sides of two anterior pairs of femora. Bristles black.|
|erythocnemius||11-14 mm||white or yellowish with a few short black ones above||dark with reddish tip. Prominent orange femur rings.||red with black apex, usually with dark marking near the middle of the anterior side||red||ventral profemur bristles weak and white, but lacking the fine white hairs on femur as in M. snowii. White bristles posteriorly on the protibia.|
|floridensis||14-15 mm||straw yellow, upper part with black bristles||Blackish except for distal fifth to third of the posterior aspects, which are reddish.||reddish with black tips, black spot on middle of the inner side||reddish with black tips||black bristles, underside of front femora with white hairs (based on limited observations)|
|lecythus||18-21 mm||black above and yellowish below||black with red tips||yellow with black tips||yellow|
|paropus||13-17 mm||yellowish with few black hairs||dark with reddish tip||dark with yellowish tip||dark with yellowish tip||Ventral profemur bristles stout and black.|
|snowii||15-20 mm||mostly black||dark with reddish tip||mostly orange. Front and middle tibiae with a ring near the middle and the apex black.||underside of front femora with long fine hairs|
Yellowish mystax with some black hairs. Long fine white pile under the sides of two anterior pairs of femora is apparently distinctive for this species. Leg bristles black.
Size: 16-21 mm
FL Season: April – May
FL Range: Panhandle
Golden-faced. Mostly white or yellowish mystax. Dark femur with reddish tip, prominent orange femur rings, ventral profemur bristles weak and white, but lacking the fine white hairs on femur as in M. snowii. White bristles posteriorly on the protibiae.
Size: 11-14 mm
Season: July – August in northeastern US
Hine (1909) indicated a record from Punta Gorda in November, which was likely M. floridensis which had not yet been described. Likely erroneous in Florida.
Straw yellow mystax with some black bristles above. Femora blackish except for distal fifth to third of the posterior aspects, which are reddish. Tibiae reddish with black tips, black spot on middle of the inner side. This makes the legs look mottled. Wings are reddish and subhyaline. Occipital bristles are black.
Size: 14-15 mm
FL Season: August – November. One April record.
FL Range: Peninsula
Male found by Chris Rorabaugh in Orange County
Femora black with red tips. Mainly yellow tibiae. Occipital hairs black and yellowish.
Size: 18-21 mm
Season: May – June in GA. Unsure if occurs in Florida.
Habitat: “rank riparian vegetation or unmowed grasslands” (Bedell, 2010)
Yellowish mystax. Dark femur with reddish tip. Dark tibia with yellowish tip. Ventral profemur bristles stout and black. Occipital hairs yellow, but this trait varies.
Size: 13-17 mm
FL Season: June
FL Range: Gainesville record. May be erroneous in Florida.
Mostly black mystax. Dark femur with reddish tip. Underside of front femora with long fine hairs. Mostly orange tibiae. Front and middle tibiae with a ring near the middle, and the apex black.
Size: 15-20 mm
Season: June – September in eastern U.S. and Canada
FL Season: April
FL Range: Panhandle
Published diagrams of male genitalia from Hine (1909), Bromley (1940), and Baker (1970)
Baker, N. T. (1970). A taxonomic and ecologic study of the asilidae of Michigan (Doctoral dissertation, Michigan State University. Department of Entomology).
Bedell, P. (2010). A preliminary list of the robber flies (Diptera: Asilidae) of Virginia. Banisteria, 36, 3-19.
Bromley, S.W. (1940). New U.S.A. robber flies (Diptera: Asilidae). Bulletin of the Brooklyn Entomological Society 35(1): 13-21.
Bromley, S. W. (1950a). Florida Asilidae (Diptera) with description of one new species. Annals of the Entomological Society of America, 43(2), 227-239.
Bromley, S. W. (1950b). Records and descriptions of Asilidae in the collection of the University of Michigan Museum of Zoology (Diptera).
Bullington, S. W., & Beck, A. F. (1991). A new species of Machimus Loew (Diptera: Asilidae) from burrows of Gopherus polyphemus (Testudines: Testudinidae). Annals of the Entomological Society of America, 84(6), 590-595.
Hine, J. S. (1909). Robberflies of the genus Asilus. Annals of the Entomological Society of America, 2(2), 136-170.
McAtee, W. L., & Banks, N. (1920). District of Columbia Diptera: Asilidae. Proceedings of the Entomological Society of Washington, 22(1), 21-33.