Efferia

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.

Male Efferia tabescens with a Little Blue Dragonlet dragonfly

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.

SpeciesSizeTibiaTarsiMale abdomenOvipositorMystax
albibarbis13-20 mmYellowish red. Tips darker.Yellowish red6 & 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
aestuans14-28 mmBrown. Tips black.Black5, 6 & 7 silvery plus posterior margin of 4Long. 6 mmBlack intermixed with white or yellow hairs
femorata26-32 mmDark reddishDark reddish5, 6, & 7Even longer. Over 7 mmBlack intermixed with white or yellow hairs
apicalis11-22 mmVariable, usually honey yellowish / bright yellow. Tips black.Black6 and 7 usually entirely silvery except for a small narrow brown spot sometimes on 64-5 mm
Abruptly narrowed beyond the basal third of its length.
Pale yellow below, black bristles above
tabescens15-23 mmVariable, pale yellowish to reddish. Tips black.  Black7 wholly silvery, posterior margin of 6 white, and brown or black dorsally.4-5 mm, gradually narrowing apicallySparse. White with 12-15 black bristles above
slossonae14Black Black5, 6 & 7 silveryover 4 mmMostly white with a number of black bristles in upper part
pogonias16-30 mmDark or very dark reddish Black6 and 7 bright whiteNot swordlike. Rounded and dark.Yellowish
nemoralis23-30 mm Reddish Black3-6 silvery. Apex of 3 and 4 with white parted hair.4.6-6.5 mm 

Efferia albibarbis

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 Range: Throughout, but most often found along beaches.

Efferia aestuans

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).

Size: 14-28 mm

FL Season: March – October

FL Range: Throughout

Efferia femorata

Silver on male abdominal segments 5-7. Tibia dark reddish. Tarsi reddish too. Ovipositor extremely long and thin (over 7 mm).

Size: Large. 26-32 mm

FL Season: April – September

FL Range: Throughout based on museum records

Example of a female with red tibia and tarsi, and a very long and thin ovipositor

Efferia apicalis

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

Efferia tabescens

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

Efferia slossonae

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. 14 mm

FL Season: March – May

FL Range: North and central Florida. I thought this was a Florida endemic, but apparently there is now a Georgia record!

Efferia pogonias

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.

Efferia nemoralis

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: 24-30 mm

Season: June – August outside of FL

Range: Possible in Florida panhandle.

Efferia stylata

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.

References:

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.

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