As this thread is over six years old, please allow me to provide an update concerning the number of mayfly species by state, which is based on my digest of the following pertinent scientific papers:
*01: Distribution of mayfly species of North America, by R. P. Randolph, supplemented by the following: *02: Mayflies (Ephemeroptera) of the far western United States: Part I: Washington) by M. D. Meyer & W. P. McCafferty *03: Mayflies (Ephemeroptera) of the far western United States: Part II: Oregon) by M. D. Meyer & W. P. McCafferty *04: Additions and Emendations to The Mayflies (Ephemeroptera) Fauna Of Saskatchewan, Canada by J. M. Webb, et. al. *05: The Ephemeroptera Of North Carolina by S. R. Beaty *06: Pennsylvania Mayflies by G. A. Hoover *07: Insecta, Ephemeroptera: New Alabama state records by W. P. McCafferty & J. M. Webb *08: Insecta, Ephemeroptera: Range extensions and new records for Ontario and Canada by McCafferty, Jacobus, Webb, Meyer *09: Mayflies (Insect: Ephemeroptera) of Nevada, Unites States of America by W. P. McCafferty, R. P. Randolph *10: USGS NPWRC - Mayflies of the United States - coordinated by B. C. Kondratieff *11: A New Species of Mayfly from WV by B. C. Kondratieff and M. D. Meyer *12: The Mayflies (Ephemeroptera) Of Alaska by R. P. Randolph and W. P. McCafferty *13: Mayflies (Ephemeroptera) of the far western United States: Part III: California by M. D. Meyer & W. P. McCafferty *14: Insecta, Ephemeroptera: New and additional records for New York by Meyers, Jacobus, Kondratieff *15: New Records Of Mayflies (Ephemeroptera From Alberta, Can. by J. P. Webb and W. P. McCafferty *16: Insecta, Ephemeroptera: range extensions and new Iowa state records by McCafferty, Hubbard, and Webb *17: Nunavut Mayflies (Ephemeroptera) A Supplement For Far Northern North America by R. P. Randolph & W. P. McCafferty *18: A New Species of Caenis (Ephemeroptera: Caenidae) from Florida, USA by M. L. Pescador & B. A. Richard *19: Cercobrachys fox: Guenther & McCafferty, 2005; Sun & McCafferty, 2008; Guenther & McCafferty, 2008 *20: Cladistics, classification, and identification of the brachycercine mayflies (Caenidae) by Lu Sun & W. P. McCafferty *21: A new species and new synonym in Heptagenia ... by J.B. Webb, W.P McCafferty, and V. R. Ferris *22: A New Genus and Species of Small Minnow Mayfly from Far Northern North America by W. P. McCafferty *23: A New Species of Maccaffertium Bednarik (Ephemeroptera: Heptageniidae) by W. P. McCafferty *24: A New Species of (Baetidae); First Representative of Genus North of Mexico by W. P. McCafferty *25: Contributions to the larvae of N. American Nixe (Ephemeroptera: Heptageniidae) ... by W. P. McCafferty & M. D. Meyer *26: Insecta, Ephemeroptera: Transcontinental range extensions in western North America by F. M. Webb & W. P. McCafferty *27: A New Species of Acentrella from New York and New England by S. K. Burian & L. W. Myers *28: A New Species of Mayfly from West Virginia by B. C. Kondratieff & M. D. Meyer *29: BoldSystems - Public Data Portal - Specimen Record - Nixe joernensis by L. M. Jacobus *30: A New Genus And New Species of Baetidae from lakes and reservoirs in eastern North America by Hill, Pfeiffer, & Jacobus *31: Contributions to the Systematics of Leucrocuta, Nixe, and Related Genera (Ephemeroptera: Heptageniidaeby W. P. McCafferty *32: Phylogenetic Systematics of the Potamanthidae (Ephemeropters) by Y. J. Bae and W. P. McCafferty *33: A Revision of Subgenus Drunella by R. K. Allen and G. F. Edmunds, Jr. *34: Mayflies (Ephemeroptera) of the Great Plains. I: Nebraska by McCafferty, Kluggertanz, Randolph, Provonsha, Lawson, Kondratieff *35: Mayflies (Ephemeroptera) of the Great Plains. II: Iowa by McCafferty, Hubbard, Klubertanz, Randolph, Birmingham *36: Mayflies (Ephemeroptera) of the Great Plains. III: North Dakota by J. L. Guenther and W. P. McCafferty *37: Mayflies (Ephemeroptera) of the Great Plains. IV: South Dakota by J. L. Guenther and W. P. McCafferty *38: South Carolina Mayflies (Ephemeroptera) by W. P. McCafferty and M. D. Meyer *39: A new species of Labiobaetis Novikova & Kluge, 1987 (Ephemeroptera: Baetidae) from Washington, USA by J. M. Webb *40: Revisionary contributions to North American Ephemerella and Serratella (Ephemeroptera: Ephemerellidae) by L. M. Jacobus & W. P. McCafferty *41: Preliminary survey of the mayflies (Ephemeroptera) ... of Big Bend Ranch State Park & Big Bend Natl. Pk. by D. E. Baumgardner & D. E. Bowles *42: A revision of the genus Leptohyphes Eaton (Ephmeroptera: Leptohyphidae) in North and Central America by D. E. Baumgardner & W. P. McCafferty *43: New Species Synonyms and Records on North American Centroptilum and Procloeon (Ephemeroptera: Baetidae) by N. A. Wiersema & W. P. McCafferty *44: New and Additional Records of Mayflies (Ephemeroptera) from the Southwestern Unuted States by D. E. Baumgardner *45: The mayflies (Ephemeroptera) of New Hanpshire: Seasonality and Diversity of the Stream Fauna by Chandler, Whitmore, Burian, Burger *46: Insecta, Ephemeroptera, Baetidae: Range extensions and new state records from Kansas, U.S.A by W. P. Mccafferty & L. M. Jacobus *47: Insecta, Ephemeroptera: Range extensions and new state records from far western Montana by W. P. McCafferty & R. L. Newell *48: New records (of Plauditus cestus) from Virginia and the Northwest Territories, with notes on color variation by Gorski, Fox, McQueen, and Jacobus *49: Geographic range extention to Wyoming, USA for Paraleptophlebia praepedita by Ashley Garlick, B. C. Kondratieff, and L. M. Jacobus *99: A DNA Barcode Library for North American Ephemeroptera: etc. by Webb, Jacobus, Funk, et. al.
NC 212 SC 185 NY 181 PA 178 CA 162 ME 162 IN 156 TN 154 VA 148 OR 147 GA 142 AL 140 WI 132 OH 126 TX 126 MI 123 NH 122 KY 121 IL 117 WA 115 IA 112 WV 109 CO 107 CT 107 MO 107 MT 106 ID 100 OK 95 AR 90 ND 85 NE 85 MN 84 FL 81 UT 81 SD 80 NM 79 AZ 72 KS 67 WY 61 MS 50 AK 48 MA 46 MD 44 NV 37 LA 34 VT 28 DE 12 NJ 10 RI 0