By Arthur V. Evans
Last week, on a drizzly Thursday morning, I drove out to Cherry Orchard Bog Natural Area Preserve with my friends and colleagues Anne Wright and Paul Bedell. Straddling a power line right-of-way near the Sussex-Prince George County line, this preserve features a coastal plain acidic seep that supports an amazing assemblage of rare plants, some of which bloom in late summer. The Virginia Natural Heritage Program staff uses prescribed burns here to prevent trees, shrubs, and woody vines from choking this open wetland, and to restore and maintain this rare plant habitat. However, after yet another extended summer drought here in Virginia, surface water was nowhere in evidence.
My goal was to photograph and collect late summer beetles, while Anne and Paul focused their efforts on odonates (dragonflies and damselflies) and robber flies (Asilidae). Few beetles were out and about, so I strapped on my camera gear and knee-pads and turned my attention to photographing other insects and spiders.
Several tall and luxurious patches of sweet-scented joe pye weed, Eupatorium purpureum, grew smack dab in the middle of the power line right-of-way. These nectar-rich flowers were magnets for all kinds of insects (other than beetles!), including several species of butterflies. A dozen or so each of large showy eastern tiger swallowtails and monarch butterflies flitted from blossom to blossom, occasionally unfurling their probosces to imbibe the flower’s sweet offerings.
I decided to head into the adjacent woods by following a fire line that snaked along the edge of a recent prescribed burn. I scanned the lush wall of vegetation that delimited the surrounding woods from the burn in hopes of finding multi-legged creatures. Nearly half an hour elapsed and all I had to show for my photographic efforts was a young Carolina mantid (Stagmomantis carolina) and a black-and-yellow garden spider (Argiope aurantia).
I saw a flash of shiny black wings among the foliage. My first thought was that it might be a mourning scorpionfly, but then it became clear that it was a female robber fly (family Asilidae) dining on a small wasp. I am no robber fly expert, but this particular fly reminded me of the genus Laphria, some of which are bee or wasp mimics.
Just as I was about to take a photograph, she was gone. Fortunately, I saw her land on a nearby leaf and she was still very much in possession of her lifeless prey. I leaned in to take the shot and, with the burst of my flash, she took to the air again. I watched intently as the shiny black fly flitted along the wood’s edge and landed on another leaf. Again, I slowly inched my camera toward her and watched her black shiny body fill up the frame of my viewfinder. And again, the flash of my camera caused her to fly away and into the burn area. I tracked her through several more landings on the low growth before she landed on a log. I took my third and last shot and she was gone. During the pursuit, a slightly smaller individual of the same species, possibly a male, also crossed my path.
I slowly walked all the way around the edge of the burn and back to the car, but saw no more robber flies. I told Paul that I had photographed what I thought to be a Laphria, but he said that the dark wings didn’t really fit any Virginia species in that genus. Paul would certainly know since he had recently published the first annotated checklist of the 115 species robber flies known to occur in Virginia (Bedell, 2010). I promised to post my best photo of the fly in question on my Facebook page as soon as I returned home.
Once posted, Paul suggested that it might be the very rare Orthogonis stygia, a species not yet known to occur in Virginia. I sent Paul all three of my images and he forwarded them to Eric Fisher for confirmation. Eric, a dipterist and asilid expert (and fellow alumni of Cal State Long Beach) quickly confirmed Paul’s identification and another new state record for Virginia.
Stanley Bromley (1931) first described this pompilid wasp mimic from three specimens collected in June; two of the specimens were from North Carolina and Mississippi, while the origin of the third specimen was unknown to him. Another specimen was later recorded from Florida (Bromley, 1950). Since then, specimens of this exceptionally rare species have been found in Alabama, Arkansas, Florida, Mississippi, Oklahoma, and Texas (Taber & Fleenor, 2003; Barnes et al., 2007).
Paul and I returned to the site only two days after I snapped my photos and searched several hours for Orthogonis. Although our efforts were in vain, we have not given up! Stay tuned for further developments
Barnes, J. K., N. Lavers, and H. Raney. 2007. Robber flies (Diptera: Asilidae) of Arkansas, U.S.A.: Notes and a checklist. Entomological News 118: 241-258.
Bedell, P. 2010. A preliminary list of the robber flies (Diptera: Asilidae) of Virginia. Banisteria 36: 3-19.
Bromley, S.W. 1931. New asilidae with a revised key to the genus Stenopogon Loew: (Diptera). Annals of the Entomological Society of America 24: 427-435.
Bromley, S.W. 1950. Florida Asilidae (Diptera) with description of one new species. Annals of the Entomological Society of America 43: 227-239.
Taber, S.W., and S.B. Fleenor. 2003. Range extension, habitat, and review of the rare robber fly Orthogonis stygia (Bromley). Southwestern Entomologist 29: 85-87.
For more information on robber flies visit:
Asilidae (Robber Flies) Page. A Page by Roy Beckemeyer <http://www.windsofkansas.com/Basilidae/asilid.html
Family Asilidae – Robber Flies <http://bugguide.net/node/view/151/bgpage>
Giff Beaton’s Robber Flies (Asilidae) of Georgia and the Southeast http://www.giffbeaton.com/Robber%20Flies.htm>
Robber Flies <http://hr-rna.com/RNA/Robber%20main%20page.htm>
Robber Flies (Asilidae) <http://www.geller-grimm.de/asilidae.htm>
The Robber Flies of Crowley’s Ridge, Arkansas. An Illustrated Guide by Norman Lavers http://normanlavers.net/>