Efferia can be one of the more common robber flies in many habitats, but they are notoriously difficult to identify. A key to eastern species is here.
Things to look for are overall size, color of the tibia and tarsi, the extent of silver on the male abdomen, the length and shape of the female ovipositor, the color of the hairs on the mystax (face beard), and on some species the color of female abdominal segment 7, and the length of the hairs on the rear of the thorax above the wings, and wing color. The table below helps compare features and was developed using multiple sources. Unique features for identifying species in Florida are bolded.
Visual Index – Males
Visual Index – Females
|albibarbis||13-20 mm||Yellowish red. Tips darker.||Yellowish red||6 & 7 white. Part of 5 also white.||Short & conical. 3 mm. Black, brownish, or reddish basally.||White, sometimes with a few black bristles on upper margin|
|aestuans||14-28 mm||Brown. Tips black.||Black||5, 6 & 7 silvery plus posterior margin of 4||Long. 6 mm||Black intermixed with white or yellow hairs|
|femorata||26-32 mm||Dark reddish||Dark reddish||5, 6, & 7||Even longer. Over 7 mm||Black intermixed with white or yellow hairs|
|apicalis||11-22 mm||Variable, usually honey yellowish / bright yellow. Tips black.||Black||6 and 7 usually entirely silvery except for a small narrow brown spot sometimes on 6||4-5 mm|
Abruptly narrowed beyond the basal third of its length.
|Pale yellow below, black bristles above|
|tabescens||15-23 mm||Variable, pale yellowish to reddish. Tips black.||Black||7 wholly silvery, posterior margin of 6 white, and brown or black dorsally.||4-5 mm, gradually narrowing apically||Sparse. White with 12-15 black bristles above|
|slossonae||14||Black||Black||5, 6 & 7 silvery||over 4 mm||Mostly white with a number of black bristles in upper part|
|pogonias||16-30 mm||Dark or very dark reddish||Black||6 and 7 bright white||Not swordlike. Rounded and dark.||Yellowish|
|nemoralis||23-30 mm||Reddish||Black||3-6 silvery. Apex of 3 and 4 with white parted hair.||4.6-6.5 mm|
There is silver on male abdominal segments 6-7 plus part of segment 5. Female has a short and conical ovipositor, which is unique among Florida Efferia. Mystax (hairs on front of face) white, sometimes with a few black bristles on upper margin. Most other species will have more black in the mystax.
Size: 13-20 mm
FL Season: March – October
FL Range: Throughout, but most often found along beaches.
Silver on male abdominal segments 5-7 plus posterior margin of 4. Thorax black with contrasting gray bands. Tibia brown or a really dull red, tips black. Female has a long sword-like ovipositor (6 mm). Some white hairs on scutum near the head as long as or longer than antennal scape in males (bottom-most antennal segment) or longer than antennal pedicel (second segment) in females.
Size: 14-28 mm
FL Season: March – November
FL Range: Throughout
Silver on male abdominal segments 5-7. Some individuals show silver on the posterior edge of segment 4. Tibia dark reddish. Tarsi reddish too in most individuals. Ovipositor extremely long and thin (over 7 mm). Short black hair on scutum near the head.
Size: Large. 26-32 mm
FL Season: April – September. One November record.
FL Range: Throughout based on museum records
Example of a female with red tibia and tarsi, and a very long and thin ovipositor
Silver on male abdominal segments 6-7 except for a small narrow brown spot sometimes on 6. Tibia color variable, but usually honey yellowish or bright yellow with tips black. Ovipositor abruptly narrowed beyond basal third of its 4-5 mm length. Female abdominal segment 7 shining black. Mystax pale yellow below, black bristles above.
Size: Small. 11-22 mm
FL Season: April – October
FL Range: Throughout
Silver on male segment 7 plus margin of 6. Segment 6 brown or black dorsally otherwise. Ovipositor 4-5 mm, gradually narrowing apically. Tibia color variable, pale yellowish (Wilcox, 1966) to reddish. Sparse white mystax with black bristles above. Segment 7 brownish pollinose above in female, though this may not always be visible. Hair on legs almost wholly white.
Size: 15-23 mm
FL Season: April – October
FL Range: Throughout
Tibiae black along with rest of leg. Silver on male segments 5-7. Ovipositor longer than 4 mm. Long black hair and bristles on top of thorax.
Size: Small. 12-14 mm
FL Season: February – May
Range: Seemingly disjunct eastern Georgia population, then scattered populations south to Highlands County and Martin County, FL (latter found by Mikie Green in 2023)
Habitat: Appears to be limited to areas with deep sand, especially fossil sand ridges. Typical habitat is scrub, though it also occurs in sandhills.
Last two abdominal segments bright white. Dark brown thorax and abdomen. Dark legs. Mystax yellowish. Dark wings.
Size: 16-30 mm
Season: May – October in NC, though mostly fall. Unsure if Florida records are valid.
Very similar to E. nemoralis. Abdominal segment 3 mostly shining black or dark brown dorsally with many black setae and without V-notch at midline. White on male abdominal segments 3, 4, 5, 6 & 7. Long white hairs on segments 3 and 4. Scutellum with black hair and bristles. Ovipositor 5-7 mm. Abdomen with large black markings dorsally.
Size: 19-29 mm
Season: May – July outside of FL
Range: OK, KS, and NE east to VA and GA. Possible in FL.
Very similar to E. plena. Abdominal segment 3 shining dark brown to black dorsally on anterior half, almost devoid of black setae, and with broad, posterior silvery pollinose band V-notched at midline. White on male abdominal segments 3, 4, 5, 6 & 7. Long white hairs on segments 3 and 4. Scutellum with black hair and bristles. Ovipositor 5-7 mm. Abdomen with large black markings dorsally. The mystax and ventral hairs of femora and tibiae are usually straw yellow or sordid white and are usually paler than in E. plena.
Size: 21-28 mm
Season: June – August outside of FL
Range: TX, OK, AR, LA, and MS. Possible in western FL panhandle.
Erroneous in Florida. Scarborough & Perez-Gelabert (1994) found the formerly published Florida record incorrect. The species only occurs in Puerto Rico and the Virgin Islands.
Figures from Wilcox (1966)
Barnes, J. K. (2007). The identity and distribution of Efferia plena (Hine) and E. nemoralis (Hine)(Diptera: Asilidae). Proceedings of the Entomological Society of Washington, 109(1), 208.
Bullington, S. W., & Lavigne, R. J. (1984). Description and habitat of Efferia kondratieffi sp. nov. with notes on Efferia aestuans (L.)(Diptera: Asilidae). Annals of the Entomological Society of America, 77(4), 404-413.
Hine, J. S. (1919). Robberflies of the genus Erax. Annals of the Entomological Society of America, 12(2), 103-154.
Scarbrough, A. G., & Perez-Gelabert, D. E. (1994). Review of the West Indian species of Efferia Coquillett (Diptera: Asilidae) with 13 new species and checklist: Part II. Hispaniola, Puerto Rico, and Lesser Antilles including Tobago and Trinidad. Zootaxa, 66, 30.
Wilcox, J. (1966). Efferia Coquillett in America North of Mexico. Proceedings of the California Academy of Sciences, 4th series., 34:85-234.