A little while ago I posted about a strange fly that had been shown to me at the Natural History Museum. It looked clearly like a phasiine tachinid but it lacked hypopleural bristles, which would normally mean that it would key as a muscoid, not an oestroid fly. It’s a very perplexing specimen but at first I thought that it could just be an aberrant Trichopodini.
I posted the fly photos on Facebook and Rodrigo Dios in São Paulo got in touch to say that he was pretty sure that there was a genus of tachinid that was notorious for having no hypopleural bristles and it was mentioned in Wood (2010) Manual of Central American Diptera (Tachinidae) – Tarassus Aldrich, 1933. He later tracked down a copy of the type description of Tarassus shannoni (Aldrich, 1933) from Mato Grosso, NW Brazil, which seemed to match the specimen.
The holotype was lodged in the National Museum of Natural History (Smithsonian Institute, Washington) so I contacted Norm Woodley and sent him my photos to see if he would be able to compare them. Recently he confirmed that my photos look identical to the holotype, except that the holotype is in much worse condition – having lost both wings, one wing being glued to a card mount. The appearance, combined with the relatively similar distributions would indicate that the NHM specimen is Tarassus shannoni.
This is a significant find because the NMNH has no other specimens and the NHM only has this one, so it is a very rare species and taxonomically very interesting. More work needs to be done on it to work out its placement but I feel that DNA should settle the issue one way or another. The only problem is finding a specimen that has a spare leg that we can use for testing 🙂