Ospriocerus abdominalis

Photo details: Canon 100mm macro lens on Canon EOS 50D, ISO 100, 1/250 sec, f/14, MT-24EX flash 1/4 power w/ diffuser caps.

Photo details: Canon 100mm macro lens on Canon EOS 50D, ISO 100, 1/250 sec, f/14, MT-24EX flash 1/4 power w/ diffuser caps.

My dipteran digression continues with this photograph of the robber fly, Ospriocerus abdominalis (Diptera: Asilidae).  More than just a pretty picture, this represents yet another apparently new state record that I and my colleague Chris Brown discovered a few weeks ago during our 2-day survey of Missouri’s critically imperiled hilltop prairies in the extreme northwest corner of the state.  Like the previously discussed Cylindera celeripes (swift tiger beetle) and Beameria venosa (a prairie-obligate species of cicada), O. abdominalis has not previously been recorded further east than Nebraska, Kansas, Oklahoma and Texas. This large fly is a grassland denizen that ranges over western North America and into Mexico (Cannings 1998, as Ospriocerus aeacus). It is somewhat suggestive of a mydas fly, although its short antennae immediately identify it as a robber fly (mydas flies have elongate clubbed antennae).  It also reminds me of the magnificent western robber fly Wyliea mydas by its mimetic, wasp-like coloration – presumably modeled after spider wasps of the genus Pepsis and Hemipepsis (Hymenoptera: Pompilidae) – but is distinguished by its black body and wings with red dorsal coloration on the abdomen (W. mydas has the abdomen wholly black and the wings red).  While not quite as handsome as W. mydas, it is impressive nonetheless.

The dry hilltop prairie remnants in which O. abdominalis, B. venosa, and C. celeripes were found are associated with the Loess Hills, a unique landform along the western edge of Iowa that reaches its southern terminus in extreme northwest Missouri.  Due to their extreme rarity and vulnerability to woody encroachment and anthropogenic degradation, these remnant habitats are considered one of Missouri’s most critically imperiled natural communities. Only about 50 acres of original habitat remain, and of this only half is in public conservation ownership.  Many of the plants and animals found in these habitats represent hypsithermal relicts that migrated eastward during a dry and warm period after the last ice age and were then “left behind” in pockets of relictual habitat as a return to cooler, wetter conditions forced the main populations back to the west.  More than a dozen plants and two vertebrates occurring in these prairies are listed as species of conservation concern.  As is typically the case, the flora and vertebrate fauna of these remnant habitats have been fairly well characterized, while precious little attention has been given to the vastly more diverse invertebrate fauna.  As we begin to study the insects of these habitats more carefully, we are almost sure to find a great many species that are more typically found further to the west and that live nowhere else in Missouri.  Their continued presence in the state will be wholly dependent upon the critically imperiled habitats in which they live, making conservation and restoration of the remaining loess hilltop prairie remnants in Missouri all the more important.

My thanks to Eric Fisher and Herschel Raney for confirming the identity of O. abdominalis.


Cannings, R. A. 1998. Robber Flies (Insecta: Diptera: Asilidae), in Smith, I. M., and G. G. E. Scudder, eds. Assessment of species diversity in the Montane Cordillera Ecozone. Burlington: Ecological Monitoring and Assessment Network.

Copyright © Ted C. MacRae 2009

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18 thoughts on “Ospriocerus abdominalis

  1. Great picture. I love robber flies. I have actually found this species in Southwestern Illinois. The hill prairies in that area have quite a diverse assortment of asilids.

    • Hi Mike, thanks for stopping by.

      You should let Herschel or Eric know about finding this species in Illinois – I’m sure they’ll find that a very interesting record. Herschel thought my Missouri record might be the easternmost for any species of Ospriocerus. I’m not surprised that it should be found even further east in hilltop prairie remnants.

  2. Great find and a terrific photo.

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      • I am already enjoying WordPress a lot. Thanks for the tip on photo linking. It works great.

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  3. Thanks Ted. Eric was the one who actually confirmed my ID. We had some correspondence when I worked at the University of Arizona.

    I wish I still lived close to Southern Illinois so that I could survey the hill prairies more thoroughly.

    Anyhow, I must say that reading your blog has really given me the itch to get back out in the field.

    • Good, sounds like the right people are getting the info.

      The field bug is hitting you again, huh? All I can say is get out there – no matter where you live, there’s interesting stuff to find. I’m in a good spot – forests to the east, prairies to the west, and a whole transition zone running right down the middle.

  4. Ted,

    Only an avid amateur; but I am thoroughly enjoying your blog since having lunch with you at the Hill Prairie Conference this past May at Augustana College in Rock Island, Illinois. I especially like the presentation of technical jargon presented in a thoroughly comprehensible manner.

    Thanks for the stellar descriptions.

    • Thanks, Trevor. Red on black seems to be a common theme in mimicry among flies. Here in North America much of it seems to be related to the spider wasp family (Pompilidae), which are black with red-orange wings. I featured a quite spectacular variation on this theme with a fly from South Africa (The “buzzard signal fly”) – black body and red head.


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