Identification, Images, & Information
For Insects, Spiders & Their Kin
For the United States & Canada

Species Efferia aestuans

Robber fly - Efferia aestuans Robber Fly - Efferia aestuans Ovipositing(?) Robber Fly - Efferia aestuans - female Robberfly - Efferia aestuans Efferia aestuans - male Efferia aestuans? - Efferia aestuans - female Asilinae (Efferia?) with Lucilia sp prey - Efferia aestuans - female Black Mustache Robber Fly - Dorsal  - Efferia aestuans - male
Classification
Kingdom Animalia (Animals)
Phylum Arthropoda (Arthropods)
Subphylum Hexapoda (Hexapods)
Class Insecta (Insects)
Order Diptera (Flies)
No Taxon (Orthorrhapha)
Superfamily Asiloidea
Family Asilidae (Robber Flies)
Subfamily Asilinae
Genus Efferia
No Taxon (Nerax group)
Species aestuans (Efferia aestuans)
Synonyms and other taxonomic changes
Nerax aestuans
Explanation of Names
Efferia aestuans (Linnaeus 1763)
aestuans = 'scolding, boiling'
Size
male 19 mm, female 21 mm (1)
Identification
tibiae partially reddish, mystax black, ventral surface of abdomen has long white hairs; female has long blade-like ovipositor

Efferia kondratieffi Bullington and Lavinge (1984) is very similar. Robberfly.org says:
" E. aestuans are longer overall. Compared to E. aestuans, males have a shorter epandrium with a different shape to the tip of the epandrium. Females have a shorter ovipositor (3-4 mm) than E. aestuans (5-7 mm) giving it a more stout appearance, and a shoter arista (tip of antennae) (0.6-0.85 mm in E. kondratieffi vs. 0.7-1.2 mm in E. aestuans)."
Bullington and Lavigne (1984) also identify a possible additional species (Tex-coastalis) from Oklahoma and Texas. Current (2024) status of this taxon is unclear.
Reference: Bullington and Lavigne (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. DOI:10.1093/aesa/77.4.404 (Research Gate link)
Range
NH-ON-FL to ND-WY-UT-NM(2)
Remarks
The most likely robber fly to land on humans. (comment by Herschel Raney)
Sometimes fearless. The males are much less common and harder to approach. (comment by Herschel Raney)
The commonest species of Asilinae in the northeast (comment by Herschel Raney)
The type species of Efferia
See Also
E. albibarbis has white mystax, and shorter, more cone-like ovipositor
Efferia kondratieffi (see Remarks here)
Internet References