These large predators are conspicuous and are typically a little larger than Promachus. Some, like P. fulviventris, are fairly distinctive, and others can be difficult to ID. The females all have a long, tapered abdomen with a circlet of spines at the tip. This page includes all species known from the eastern coastal states.
Visual index
White-sand Marauder (Proctacanthus fulviventris)
Based on records in iNaturalist, this may be one of the most common robber flies in Florida. It may also be that they are large and beautiful and often perch on white sandy trails where people are hiking.
Note the bicolored legs with black femurs, orange hairs on face and thorax, and red on abdomen. There is less red on the abdomen of females, but it’s usually visible under the wings. The thorax is also typically black. Males also have the last few abdominal segments thickened – a trait shared by P. hinei. The hypopygium (male genitalia) are short. Note that the proboscis curved upward.
Size: 25-30 mm
Range: GA and FL
FL Range: Throughout. These love white sand, so they occur primarily from central Florida and south, but have also been recorded from north Florida and coastal areas of the Panhandle.
FL Season: Late March – November
White-sand Marauder (Proctacanthus fulviventris) variation
The primary character distinguishing P. fulviventris in the literature is that they have black femurs. However, some individuals like this one have red femurs and the scutum (top of thorax) is also red. Note this individual is found in the same white-sand habitat where P. fuliventris is expected, and the hairs on the face (occipital hairs, mystax, beard) are all orangey-yellow as is expected on P. fulviventris. Perhaps this is a fresh individual that may turn darker with age.
Giff Beaton also has found P. fulviventris with entirely red legs.
Eastern Red-tailed Marauder (Proctacanthus rufus)
I typically find these in riparian areas along sandy rivers where they can be abundant. They are very similar to P. hinei which may not be confirmed east of the Mississippi. The last few abdominal segments bulge from beneath in male P. hinei and there is no bulge in P. rufus. Entirely reddish legs and scutums (top disc of thorax). Red abdomens. The proboscis curves upward. White or yellowish mystax, beard, and occipital bristles. Females may be indistinguishable from P. hinei.
Size: 30-36 mm
Range: All eastern U.S. states and New Brunswick
FL Range: Panhandle and north Florida south to Gainesville
FL Season: June – July
Short-winged Marauder (Proctacanthus brevipennis)
Bicolored legs. Strongly marked scutum (top of thorax). Ovipositor of females can be black or red. Short wings — hence the name.
Size: 20-28 mm
Range: U.S. east of Rockies
FL Range: Throughout
FL Season: March – June. Records from later in the summer may be misidentified. This is one of the first robber flies on the wing in spring and is typically the only Proctacanthus in March and April.
Violin Marauder (Proctacanthus gracilis)
These often have well-defined violin-shaped markings on the scutum (top disc of thorax). These markings may be less distinct on other individuals perhaps because of age. Note yellowish pruinosity on top of reddish/purple ground color of thorax and reddish wing veins. Unlike P. longus and P. brevipennis, only the last abdominal segment of females is polished black (thanks to Mikie Green for noticing this female character). Wings short.
Size: 26-30 mm
Range: Southeast (MS, AL, GA, FL, SC, NC)
FL Range: Panhandle, north and central Florida south to Hillsborough County.
FL Season: May – September
Long-winged Marauder (Proctacanthus longus)
Abdomen brown. Wings uniformly brown and long. Thorax brown, gray pollinose. Male genitalia shorter than last two abdominal segments combined. Occipito-orbital hairs part black and part pale. Mystax yellow, palpi black with pale hairs, though some central Florida sandhill populations have a black and white mystax and black hairs on the palpi.
Size: 32-36 mm
Range: Southern and southeastern U.S. north to Virginia, west to Texas and Oklahoma.
FL Range: Panhandle, north and central Florida south to Highlands County
FL Season: May – early October
Long-winged Marauder (Proctacanthus longus) variation in central Florida
The autumn Proctacanthus found in central Florida sandhills have long, brown wings and reddish legs and poorly marked scutums. These are traits of Proctacanthus longus. However, note that this population all have black and white hairs on the mystax. The description of P. longus and milberti in Hine (1911) both indicate a pale mystax, though P. philadelphicus has black hairs mixed with yellow. The central Florida individuals also have black hairs on the palpi, which is a character shared by P. milberti and P. philadelphicus according to Hine (1911). P. longus has pale hairs on the palpi. These appear to be a variation of P. longus, and Hine’s key does not work with them. Teagan Mulford is currently researching Proctacanthus, and she thinks these are P. longus based on genitalia morphology.
Common Marauder (Proctacanthus milberti)
This is very similar to P. longus. Mystax yellow, palpi black with black hairs. Thorax gray. Legs also grayish purple. Male genitalia shorter than last two abdominal segments. Wings uniformly light brown.
Size: 28-40 mm
Range: Throughout U.S. and Canada
Range: This species is widely distributed throughout the U.S. and Canada. Hypothetical in FL. Bromley (1950) said “northwestern part of the state.”
Season: Late July – October. Season may be one of the better ways to distinguish this species.
Northeastern Marauder (Proctacanthus philadelphicus)
Yellow mystax with some black bristles. Dark brown body. Brown wings supposedly short and narrow. Palpi with black hair.
Size: 28-36 mm
Range: Hine (1911) indicates northeastern U.S. and Canada south to Virginia, but there are museum records labeled as P. philadelphicus for all states on the east coast. Many of these are likely misidentified.
FL Range: Erroneous in Florida.
Giant Marauder (Proctacanthus heros)
These large robbers are typically found on dead trees in high quality sandhills. Note the entirely bright orange legs, yellow facial hairs, dark thorax contrasting with yellow pollinose abdomen ending with a couple entirely pale segments.
Size: Huge. 32-45 mm
Range: Southeastern U.S. west to AR and north to VA
FL Range: Throughout though uncommon
FL Season: May – September (recorded through October in NC and SC)
Black-bellied Marauder (Proctacanthus nigriventris)
Dark abdomen with the last couple segments mostly white.
Size: 30-35 mm
Range: Southeast and eastern U.S.
FL Range: Panhandle and north Florida
FL Season: May – August
Western Red-tailed Marauder (Proctacanthus hinei)
Dark purple thorax and pale red abdomens like P. rufus, but the last few abdominal segments on the males are swollen underneath. There is nothing in the literature to indicate that P. hinei females can be differentiated from P. rufus. Bromley (1928) indicates the thorax is darker on P. rufus, but this does not appear to be a consistent trait.
Size: 33 mm
Range: U.S. east of Rockies
FL Range: Likely erroneous. I cannot find any modern confirmation that P. hinei occurs east of the Mississippi River.
Proctacanthus vittatus
“The color of the thorax of vittatus is quite variable. In some specimens the mesonotal vittae are conspicuous; in others they are quite absent, the whole mesonotum being rusty reddish. The tarsi are dark reddish, more castaneous apically” (Curran, 1951).
First abdominal segment black.
FL Range: Erroneous. Known from Dominican Republic and Haiti.
References
Curran, C. H. (1951). The West Indian species of Mydas and Proctacanthus (Diptera, Mydaidae and Asilidae). American Museum novitates; no. 1507.
Bromley, S. W. (1928). Notes on the Genus Proctacanthus with the Descriptions of Two New Species (Diptera; Asilidae). Psyche, 35(1), 12-15.
Hine J.S. (1911). Robberflies of the genera Promachus and Proctacanthus. Ann. Ent. Soc. Amer. 4(2): 153-172.
Robber Flies of the Southeast 