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For the United States & Canada
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Family Asilidae - Robber Flies

spider killer - Tipulogaster glabrata Robber Fly, with prey - Diogmites discolor - female Robber Fly - Laphria posticata Wasp mimic Robber Fly - Ceraturgus fasciatus Three-banded Robber Fly - Stichopogon trifasciatus Fly Spp. - Holcocephala Promachus rufipes - male Friendly Robber - Efferia aestuans - male Killer with food - Mallophora orcina
Kingdom Animalia (Animals)
Phylum Arthropoda (Arthropods)
Subphylum Hexapoda (Hexapods)
Class Insecta (Insects)
Order Diptera (Flies)
No Taxon (Orthorrhapha)
Superfamily Asiloidea
Family Asilidae (Robber Flies)
Other Common Names
Assassin Flies(1)
Synonyms and other taxonomic changes
higher taxa recently redefined -- summary in(2); phylogeny in (3)
Explanation of Names
Asilidae Latreille 1802
see Asilus
~1,040 spp. in ~100 genera in our area, >7,500 described spp. in ~560 genera worldwide(4)(5); ~200 spp. in Canada
Overview of our fauna (* –taxa not yet in the guide; classification adapted from(6) –see note):
Family Asilidae
5-30 mm and more, typically 9-15 mm
predatory flies, often perch in exposed location and dash after prey
top of head depressed between eyes, with three ocelli in the depression
body from very hairy to nearly bare; some are bee/wasp mimics
face usually "bearded", with prominent mystax
mouthparts modified to inject prey with saliva, similar in both sexes (unlike in blood-sucking flies, such as Tabanidae)
antennae three-segmented, third segment elongate and often with terminal style
Key to Nearctic genera in (7), to world genera in (8)
most diverse in dry, open habitats; larvae usually in soil or decaying wood
Insects of many orders
These flies impale their prey, inject digestive enzymes and suck their victims dry.(9)
Life Cycle
Minimal courtship behavior. Females lay eggs in the soil or in plants. A few, such as Mallophora and Megaphorus, form an egg mass on a plant stem (photo here). Larvae often predatory, consuming eggs and larvae of other insects in decaying matter. Typically overwinter as pupa, emerge in spring. Life cycle is 1-3 years.

Eggs; larva; pupa; pupal case
Genera not yet in the guide per (4):
Bohartia 6 spp., w/sw US
Prolatiforceps 2 spp. NM-AZ
The following are represented by a single species each:
w NA: Willistonina
TX: Amblyonychus
AZ: Bromleyus, Dicranus, Orrhodops, Perasis
TX-NM: Plesiomma
CA: Dasypogon
In 2009, things were changed significantly by Torsten Dikow(10)(11) with publication of his PhD work. His morphology-only analysis of 158 spp. yielded 720 most parsimonius cladograms, the favored classification selected being one comprised of 14 subfamilies. A combined total evidence analysis was then performed, adding DNA sequencing data from 77 of the original 158 spp. studied (representing 12 of the 14 subfamilies sampled morphologically). Results from the combined total evidence analysis failed to support the morphology-only classification in many instances, with about half of the subfamilies appearing in multiple positions (=nonmonophyletic) in the favored combined cladograms.
Another problem is that some of the subfamilies recognized lack external characters useful for dichotomous keys or gestalt recognition: many features used in the morphology data matrix require extensive dissection, and those in the total evidence analysis are partly molecular. Ironically, the only truly congruent classification resulting from both methodologies is one where only three subfamilies are recognized (Asilinae, Laphriinae, Dasypogoninae), like the pioneering classifications of Macquart and Loew in the early 1800s! Dikow's work has demonstrated that some of the modern subfamilies and tribes (those more recent than the classic ones just mentioned) are not monophyletic, but problems are apparent with his new classifications as well.
More species need to be sampled for phylogenetic study – especially those with DNA sequencing data – even though total evidence analysis has so far yielded conflicting results. Until a stable, practical classification is available, some version of the Papavero classification is probably still preferable, and I recommend using the eight subfamilies from(3) (currently used on BG) with no tribes recognized (some tribes are apparently monophyletic but others are not, and details and relationships are controversial).
Print References
Dennis D.S., Barnes J.K. (2011) Tentative key to robber fly (Diptera: Asilidae) subfamilies based on pupal cases. Zootaxa 3031: 37–46 (Full text)
Internet References
Works Cited
1.The families and genera of North American Diptera
Charles H. Curran. 1934. Ballou Press, New York, NY.
2.Dikow T. (2004–2012) AsilidaeData -- web-site version 2
3.The phylogeny of robber flies (Asilidae) inferred from ultraconserved elements
Cohen C.M., Noble K., Cole J.T., Brewer M.S. 2021. Sys. Entomol. 46: 812-826.
4.Information on robber flies, compiled by F. Geller-Grimm
5.Order Diptera Linnaeus, 1758. In: Zhang Z.-Q. (ed.) Animal biodiversity: An outline of higher-level classification...
Pape T., Blagoderov V., Mostovski M.B. 2011. Zootaxa 3148: 222–229.
6.Catalog of the robber flies (Diptera: Asilidae) of the Nearctic Region [unpublished draft]
Fisher E.M., Wilcox J. 1997. 45 pp.
7.Robber Flies
8.Robber flies of the world: the genera of the family Asilidae
Hull F.M. 1962. USNM Bull. 224: 1-907.
10.Phylogeny of Asilidae inferred from morphological characters of imagines (Insecta: Diptera: Brachycera: Asiloidea)
Dikow T. 2009. Bull. Am. Mus. Nat. Hist. 319: 1–175.
11.A phylogenetic hypothesis for Asilidae based on a total evidence analysis of morphological and DNA sequence data...
Dikow T. 2009. Organisms Diversity & Evolution 9(3): 165–188.
12.A literature-based checklist of Kansas robber flies (Diptera: Asilidae)
Beckemeyer R.J. 2001. The Prairie Naturalist 33(2): 65-92.
13.Robber flies of Utah (Diptera: Asilidae)
Nelson C.R. 1987. Great Basin Nat. 47: 38-90.
14.Herschel Raney's Random Natural Acts: Robber Flies
15.Giff Beaton's Robber Flies (Asilidae) of Georgia and the Southeast
16.Featured Creatures: Robber Flies
17.California Robber Flies
18.Lavers N. (2007) The robber flies of Crowley's Ridge, Arkansas: An illustrated field guide
19.Beckemeyer R.J. (2001) Asilidae Page