I’m back in South America for the next 2+ weeks, and though it will be another week before I actually make it into Argentina, I am celebrating my return to that lovely country with photos of Argentinian insects taken during last year’s extended visit but that I haven’t had a chance to share before now. Earlier this week I featured Camponotus sericeiventris (though I prefer the literal translation, “silky-bellied humpbacked ant“)—easily among the most handsome ants that I’ve ever seen and which I encountered in the remnant quebracho forests at Chaco National Park in northern Argentina. Today’s feature is an equally handsome robber fly (order Diptera, family Asilidae), also seen at the park and which landed on a dead log just long enough to allow one good lateral profile shot of the beast in all its hairy splendidness! (Probably it zipped off to impale an Odontocheila tiger beetle in the back of the neck!)
I sent this photo to a few fly guys looking for a more authoritative opinion about its identity, mentioning its resemblance to some of our North American species of Efferia. Herschel Raney agreed that it belonged to at least that group, while Eric Fisher suggested a species in the genus Triorla (an early segregate of Efferia that is now widely regarded as a valid genus). The most recent checklist of robber flies from Argentina (Artigas & Hengst 1999) lists three species in the Efferia group (all in the genus Nerax); however, both Herschel and Eric confirmed my suspicion that Argentina, and especially the north, is not well studied for Asilidae. Eric further suggested that there could be as many as several times the number listed, mainly undescribed but also described from adjacent countries and occurring in Argentina but not yet recorded from there. Also, I had presumed this individual to represent a female since it lacked the distinctly swollen genital capsule (e.g. see this post, presumably another Efferia-group species), but Herschel thought the terminal structure was odd and did not look female.
Artigas, J. N. & M. B. Hengst. 1999. Clave ilustrada para los géneros de asílidos argentinos (Diptera: Asilidae). Revista Chilena de Historia Natural 72:107—150.
Copyright © Ted C. MacRae 2013