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Efferia deserti, male in side view.jpg
Efferia deserti male in side view
Scientific classification

Coquillet, 1893
Type species
Efferia candida
Coquillet, 1893

over 240, see text

  • Nerax Hull, 1962, TS: Asilus aestuans Linnaeus (orig. des.)
  • Erax of authors, not Scopoli.
A view from above of a female Efferia deserti - note the converging veins R4 and R5 at the wing tip and the narrow cell r4 between both veins; quite a few Efferia species (like this one) have a short vein stub branching off near the split of R4 from R5
Male of Efferia aestuans
Female of Efferia aestuans

Efferia is an insect genus of mainly neotropical and nearctic Diptera in the family Asilidae or robber flies. It is one of the most species-rich genera of Asilidae, with particularly high diversity in arid or semi-arid ecosystems of the New World.


Small to large-sized robber flies (10–40 mm) with distinctly different shape of the posterior end of the abdomen in males versus females. Females have a short or long ovipositor that is hairless and short conical to slender wedge-shaped, its color is usually glossy black. Males have a "helicopter tail" with glossy black claspers that are covered in hairs, forming part of a complex genital structure (the combined epandrium and hypandrium) that is clearly larger than the abdominal segments and is oriented diagonally to vertically upwards relative to the main body axis.

Abdominal coloration is usually greyish to brownish in females, versus more contrasting with silvery and/or black segments or patches in males. In both sexes the tip of the genitalia usually extends past the wing tips. Wings are clear or uniformly tinted, with tints varying from transparent brown to dark black. Venation includes a recurrent vein on R1, narrow cell r4, R4 extending roughly parallel to R5 or converging moderately with R5 towards the wing tip.


As is typical for robber flies, adult Efferia are ambush predators, taking off from a resting position on the ground or on a branch to intercept other flying insects in mid-air. Prey are taken from a wide variety of insect orders: Robert Lavigne's Predator-Prey Database for the family Asilidae[1] has 918 records for Efferia species feeding frequently on Diptera, Homoptera, Hymenoptera, Heteroptera, Coleoptera, Lepidoptera, Orthoptera, as well as a few reports of prey species belonging to Neuroptera, Odonata, Ephemeroptera - and even one record for Araneae (spiders). Other asilids are frequently preyed upon, and cannibalism is common as well.

Efferia species of deserts and grasslands can occur in high abundance, at times even exceeding one individual per square foot. They tend to perch close to the ground and often remain quite immobile - sometimes until they're about to get stepped on. Spotting them is often a matter of first hearing the typically short evasive flight, before seeing where one landed. This is especially true for the males, which emit a characteristic pulsing buzz during the few seconds in flight; this sound tends to be loud and noticeably higher pitched than that of a flying female.[2]

If you slowly approach a perched individual during hot weather then it may repeatedly fly up and grab any mosquitoes or freeloader flies circling around you, often returning to its original perch to feed for several minutes after each catch.


This is an as yet provisional list of 241 recognized species, combined from 235 entries for accepted species of Efferia in GBIF[3] plus 6 species only listed as valid in other recent sources[4][5][6]

Female Efferia basini laying eggs under bark and in cracks of dead sagebrush
Male of Efferia basini feeding on a solitary bee
Efferia female feeding on a beefly (probably Villa agrippina)
Efferia female using its wedge-shaped ovipositor to lay eggs inside a shriveled flower calyx


Combined analysis of morphological and molecular characters places Efferia pogonias in a clade corresponding to the subfamily Asilinae, usually with Proctacanthus philadelphicus as sister taxon and always resolving this subfamily as monophyletic.[9]

See also[edit]



  1. ^ http://www.geller-grimm.de/catalog/lavigne.htm Predator-Prey Database for the family Asilidae
  2. ^ Cannings, Robert A. (2011). "Efferia okanagana, a new species of robber fly (Diptera: Asilidae) from the grasslands of southern British Columbia, Canada, with notes on taxonomy, biology, distribution, and conservation status". The Canadian Entomologist. 143 (6): 578–93. doi:10.4039/n11-032.
  3. ^ https://www.gbif.org/species/1659595[full citation needed]
  4. ^ http://www.geller-grimm.de/catalog/species.htm[full citation needed]
  5. ^ http://www.fsca-dpi.org/insectamundi2008/0049Scarbroughand%20Perez.pdf Scarbrough, Aubrey G. & Daniel E. Perez-Gelabert, 2008, Insecta Mundi 0049: 1-29.
  6. ^ Scarbrough, Aubrey G.; Stevens, Lawrence E.; Nelson, C. Riley (2012). "The albibarbis-complex of Efferia Coquillett, 1910 from the Grand Canyon region, southwestern U.S.A., with three new species and new distribution records (Diptera: Asilidae)". The Pan-Pacific Entomologist. 88: 58–86. doi:10.3956/2012-07.1.
  7. ^ https://www.gbif.org/species/1665196[full citation needed]
  8. ^ https://www.gbif.org/species/1663924[full citation needed]
  9. ^ Dikow, Torsten (2009). "A phylogenetic hypothesis for Asilidae based on a total evidence analysis of morphological and DNA sequence data (Insecta: Diptera: Brachycera: Asiloidea)". Organisms Diversity & Evolution. 9 (3): 165–88. doi:10.1016/j.ode.2009.02.004.

External links[edit]