T.G.I.Flyday – Andrenosoma fulvicaudum

Andrenosoma fulvicaudum | Stone Co., Arkansas

First, about the name. T.G.I.Flyday is my contribution to a collusional triad between dipterist Morgan Jackson, myrmecologist Alex Wild, and myself (uhm, beetles).  Although Alex blogs primarily about ants, he has long featured a “Friday Beetle Blogging” series.  I’ve also occasionally stepped on their toes with an ant or fly post, so Morgan and I thought it would be fun to complete the Friday switcheroo with a post about ants on his blog and one about flies on mine. Get it?… Oh well, it made me chuckle when we thought it up.  Anyway, here is my first T.G.I.Flyday contribution.

Among the flies (order Diptera), it is hard to pick anything but robber flies (family Asilidae) as the most charismatic group.  Several subfamilies of robber flies have candidates that vie for the most impressive species, mostly due to their enormous size combined with striking green eyes (e.g., Microstylum morosum, Diogmites neoternatus) or vivid, aposematic / mimetic coloration (e.g., Archilestris magnificus, Eccritosia zamon, Wyliea mydas).  However, my favorite subfamily is the Laphriinae—not because of the amazing bumble bee-like appearance of the nominate genus, but rather the larval food of all species in the subfamily; wood-boring beetle larvae.  Over the years, I have put up hundreds of batches of dead wood for rearing wood-boring beetles in the families Buprestidae and Cerambycidae, and not uncommonly do I find in one of the emergence containers—especially those containing dead pine—an adult of one of these impressive flies. Oftentimes their characteristic pupal cases will be found protruding from the emergence hole, in which case I pin it underneath the fly (just in case some ambitious dipterist examines my collection after I’m gone and finds that the pupal case of xx species is not yet described).  I’ve by now accumulated a rather decent little robber fly collection (especially considering that I’m really a coleopterist), graciously identified for the most part by world robber fly expert Dr. Eric Fisher (California Department of Food and Agriculture).

Last weekend I made the second in a series of trips I’ll be taking to the White River Hills region of north-central Arkansas in an effort to confirm the occurrence there of Cylindera celeripes (swift tiger beetle).  My efforts are focused on the area around Calico Rock, a marvelous system of acidic sandstone barrens interspersed amongst shortleaf pine and oak forests.  The occasional dead pines found in such areas are highly attractive to a variety of pine-associated buprestids and cerambycids (my first loves), and whenever I see a standing dead tree I make a beeline straight for it (the tiger beetles can wait).

This individual was sitting on the trunk of a dead shortleaf pine with a mirid bug for prey.

On this day, sitting on the trunk of the first dead pine that I approached was not a buprestid or cerambycid, but rather this laphriine robber fly.  Based on the reddish posteriodorsal markings of the abdomen and general gestalt, I take this to be Andrenosoma fulvicaudum, a widespread though never very abundant species that occurs across most of North America.  According to Bromley (1934), the species frequents dry, sandy locations where it rests on logs, stumps, or tree trunks exposed to the bright sunlight and is commonly observed preying on small hymenopterans.  These observations are quite consistent with mine, except this one was feeding on a true bug in the family Miridae (perhaps distracting it just enough to allow me these photographs).  Cannings (1998) notes that A. fulvicaudum is attracted to recently burned forests, which will provide a fresh supply of wood-boring beetle larvae on which its larvae can prey.  This is the only species of Andrenosoma occurring in eastern North America; four additional species are restricted to Texas and a fifth occurs only in the western U.S., but the genus reaches its greatest diversity in the Neotropics.


Bromley, S. W. 1934. The Laphriine Robber Flies of North America.  Ph.D. dissertation, Ohio State University, 358 pp.

Cannings, R. A. 1998. Robber flies (Insecta: Diptera: Asilidae), In I. M. Smith 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 2011

19 thoughts on “T.G.I.Flyday – Andrenosoma fulvicaudum

  1. Great post – quite a few robber flies have turned up on invertebrate surveys I’ve done in southern England (often Machminus species), and we do have the impressive ‘Hornet Robber Fly’ Asilus crabroniformis, though it’s uncommon these days. Good luck with the hunt for C. celeripes!

  2. Love the convergence on the series title! Blogging evolution perhaps?

    Also love the photos! It’s hard not to be attracted to a top predator when it looks like this! The lions of the skies!

    • Honestly, I didn’t think of the title until after I saw yours. When I did, it popped into my head instantly!

      I’m kicking myself about the other laphriine robber I saw sitting on the same tree trunk but could not get a photo of before it zipped off – Laphria saffrana!

  3. I’m not so sure that the robber flies are always the top predators; yesterday while pushing my bike up the hill, I saw an ant dragging the corpse of a robber fly across the road. The robber fly was at least ten times the size of the ant. Pity I didn’t have a camera at the time. I always see the best bugs when I don’t have either a camera or a container.

    (OK, so the robber fly was probably killed by something else and the ant was just dragging it home. Maybe not, though).

  4. Great Post! I can remember a collecting trip when i saw a rober fly taking to the ground a darner dragon fly that had to weigh 3 to 4 times its own weight -Beetlebrained

  5. I have always been partial to Empididae complete with nuptial gifts – such generous swains ! But Asilidae will do in a pinch

    a pun !

  6. Once again, Arkansas glades come through! Glad you made your way down Arkansas way. This natural state is extremely diverse and I have worked 38 years in trying to elucidate this incredible biodiversity! Great photos Ted!

    • I’ve become enamored with Arkansas since my two June visits and have a huge appetite to explore it more thoroughly. I still have lots of photos to share from those trips!

      As always, thanks for your kind comments.

  7. Pingback: Ozark Landscapes – White River in northern Arkansas « Beetles In The Bush


Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s