Description of the Nymph of Ophiogomphus smithi (Odonata: Gomphidae), With a Key to the Species of Ophiogomphus in the Western Great Lakes Region

Ophiogomphus smithi Tennessen & Vogt is a gomphid dragonfly with restricted distribution which includes northeast Iowa, southeast Minnesota, and central to northwestern Wisconsin. The nymph is described and illustrated based on 173 specimens (66 exuviae of reared specimens plus 107 nymphs) from throughout the species’ range. The nymph of O. smithi is very similar to nymphs of O. carolus Needham, O. colubrinus Selys, and O. rupinsulensis (Walsh). Nearly all (99%) of O. smithi sampled can be distinguished from O. colubrinus by prementum terminal width less than or equal to 2.97 mm (98% of O. colubrinus greater than 2.97 mm), and from O. carolus and O. rupinsulensis by the ratio of metatibia length to abdominal segment 10 width being greater than 1.66 (96% of O. smithi) vs. less than 1.66 (98.5% of O. carolus and O. rupinsulensis). Several characters and character combinations previously unused for Ophiogomphus nymphs were found to be of taxonomic value, including color pattern on dorsal hooks and dorsum of abdomen, shape of abdominal mid-dorsal punctae, length and shape of fronto-clypeal ridge setae, and ratio of metatibia length to width of abdomen on segments 9 and 10. An illustrated quantitative key to the 7 species of Ophiogomphus occurring in the western Great Lakes region is provided, along with a separate, more qualitative key enabling species identification in the field. Ophiogomphus smithi is regularly syntopic only with O. rupinsulensis, rarely with O. carolus and O. colubrinus and not with O. anomalus, O. howei, or O. susbehcha; nymphs inhabit small to medium-sized, sandy, cool to warm stream segments with patches of pea-sized gravel.