This paper describes 11 of 18 new species recognised in the recent book, 'Field Guide to the Flower Flies of Northeastern North America'. Four species are omitted as they need to be described in the context of a revision (three Cheilosia and a Palpada species) and three other species (one Neoascia and two Xylota) will be described by F. Christian Thompson in a planned publication. Six of the new species have been recognised for decades and were treated by J. Richard Vockeroth in unpublished notes or by Thompson in his unpublished but widely distributed 'A conspectus of the flower flies (Diptera: Syrphidae) of the Nearctic Region'. Five of the 11 species were discovered during the preparation of the Field Guide. Eight of the 11 have DNA barcodes available that support the morphology.
New species treated in this paper include: Anasimyia diffusa Locke, Skevington and Vockeroth (Smooth-legged Swamp Fly), Anasimyia matutina Locke, Skevington and Vockeroth (Small-spotted Swamp Fly), Brachyopa caesariata Moran and Skevington (Plain-winged Sapeater), Brachyopa cummingi Moran and Skevington (Somber Sapeater), Hammerschmidtia sedmani Vockeroth, Moran and Skevington (Pale-bristled Logsitter), Microdon (Microdon) scauros Skevington and Locke (Big-footed Ant Fly), Mixogaster fattigi Locke, Skevington and Greene (Fattig's Ant Fly), Neoascia guttata Skevington and Moran (Spotted Fen Fly), Orthonevra feei Moran and Skevington (Fee's Mucksucker), Psilota klymkoi Locke, Young and Skevington (Black Haireye) and Trichopsomyia litoralis Vockeroth and Young (Coastal Psyllid-killer). Common names follow the 'Field Guide to the Flower Flies of Northeastern North America' (Skevington et al. 2019).