| 1a. Gills of abdominal segment 2 operculate, covering suceeding gills | |
| 1b. Gills of abdominal segment 2 similar to other gills or absent | |
| 2a. Gills of abdominal segment 2 triangular or subtriangular, not meeting medially; gill lamellae on segments 3-6 simple; forefemora with transverse row of long setae FAMILY LEPTOPHYIDAE | |
| 2b. Gills on abdominal segment 2 quadrate, almost meeting medially; gill lamellae on segments 3-6 with fringed margins. FAMILY CAENIDAE | |
| 3a. Gills absent from segment 2 FAMILY EPHEMERELLIDAE | |
| 3b. Gills present on segment 2 | |
| 4a. Gills bifid or forked; 3 caudal filaments FAMILY LEPTOPHLEBIIDAE | |
| 4b. Gills single plates; 2 or 3 caudal filaments | |
| 5a. Nymphs dorsal-ventrally flattened; eyes and antennae on dorsal surface of head. FAMILY HEPTAGENIIDAE | |
| 5b. Nymphs cylindrical or otherwise; eyes and antennae positioned laterally on head | |
| 6a. Antennae longer than 2X the width of the head(often 3X); median caudal filament reduced or well developed . . . | |
| 6b. Antennae shorter than 2X the width of the head; median caudal filament always well developed | |
| 7a. Maxillae ends with pectinate spines used for grazing or collecting detritus?;gills oval with stripe along outer margin FAMILY AMELETIDAE Ameletus | |
| 7b. Maxillae ends without pectinate spines;gills on abdominal segments 1 and 2 subtriangular FAMILY SIPHLONURIDAE |
ReferencesEdmunds,GF; Tennessen,KJ 1996 Ephemeroptera. In: An Introduction to the Aquatic Insects of North America. 3rd ed. Eds: Merritt,RW; Cummins,KW Kendall/Hunt Publishing Company, Dubuque, Iowa, 126-163.Ward,JV, Kondratieff,BC and Zuellig,RE 2002 An Illustrated Guide to the Mountain Stream Insects of Colorado. 2nd ed. University Press of Colorado, Boulder, Colorado. 219 pages. Good LinksOn this website:Key to the Adult Mayflies Other Websites: Digital Key to the Ephemeroptera of North Dakota http://www.waterbugkey.vcsu.edu/php/familykey.php?idnum=8&o=Ephemeroptera1L&type=family Brown, Wendy S. 2004 Mayflies (Ephemeroptera) of Gunnison County, Colorado, USA www.gunnisoninsects.org |