For the determination it is necessary to have both sexes. For example, the ovipositor can help to identify the right genus and the male genitalia help with the identification of the species. Because of the small size of these features a stereo-microscope must be used.
Photographs are an additional source for identification, but they are not an alternative for keys with detailed drawings. If you do not have a big collection, you can try to check your determination by comparing the material with the photographs on this DVD. Most of the time it is not necessary to ask a specialist to confirm the determination.
The maxim is: The easier a group of species can be determined, the more people will work on it.
Additional information on robber flies (such as distribution records, literature, and a world catalogue of robber flies) is available on the Internet. This website is intended to complement the DVD
There are only a few entomologists with a special interest in robber flies. The co-operation and mutual help of a higher number of workers will increase the knowledge of these flies substantially.
The characters used in the keys are based on the literature, several hints of colleagues and our own observations. There remain some taxonomic and systematic problems although North America has a high standard in entomology. Some have an unclear status (e.g. some Asilinae genera). Therefore, it is necessary to check them in detail and to inform the other workers on the results.
A general problem will always remain: We usually work on little material, which represents a fraction of a local population. The examination of material from different populations is rarely possible but we need much more information on the variation of the species.

The following taxa are not considered:

• Asilus astutus Williston, 1893
• Asilus auricomus Hine, 1909
• Asilus carolinae Martin & Wilcox, 1965
• Asilus citus Hine, 1918
• Asilus comosus Hine, 1918
• Asilus delicatula Hine, 1918
• Asilus fattigi Bromley, 1940
• Asilus frosti Bromley, 1950
• Asilus hubbelli Bromley, 1950
• Asilus humilis Bellardi, 1861
• Asilus longicella Macquart, 1850
• Asilus piceus (Hine, 1909)
• Asilus platyceras (Hine, 1922)
• Asilus sackeni Banks, 1920
• Asilus vescus Hine, 1918 [= Tolmerus?]
• Dasypogon quadrinotatus Bigot, 1878
• Dasypogon rubiginosus (Bigot, 1878) [as Selidopogon]
• Eutomus lecythus (Walker, 1849)] [as Asilus]
• Stilpnogaster auriannulatus Hine, 1906

• private collection: Fritz Geller-Grimm [COGG]
• private collection: Dr. Eric M. Fisher [COEF]
• public collection: "National Museum of Natural History", Washington D.C., USA [USNM]
• public collection: "American Museum of Natural History", New York, USA [AMNH]
• public collection: "Cornell University, Insect Collection", Ithaca, USA [CUIC]
• public collection: "Florida State Collection of Arthropods", Gainesville, Florida, USA [FSCA]
• public collection: "Museum für Naturkunde", Berlin, Germany [ZMHB]
• public collection: "Snow Entomological Collection, University of Kansas, Natural History Museum and Biodiversity Research Center", Lawrence, Kansas, USA [SEMC]
• public collection: "Zoologische Staatssammlung", München, Germany [ZSMC]