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Ephemeroptera of Gunnison County, Colorado

Adult key to Mayfly Families

Under construction :-) 3 June 2008

This is a first attempt at rearranging the adult mayfly key from Merritt, Cummins and Berg to fit our local mayfly families, here goes! I do not have keys for most of the families so most links go to an introduction to that family. This key is greatly abbreviated, if you're very far away from the central Colorado mountains there will be more families, use Merritt, Cummins and Berg for more information.

1a. Cubital intercalaries of forewing are a series of veinlets, sometimes forking or sinuate, which attach the CuA vein to the hind margin of the forewing.
1b. Cubital intercalaries of forewing variable, sometimes absent, but not as above.
2a. Claws dissimilar, one sharp and one blunt.
2b. Both claws similar and sharp.
3a. 3-tailed
3b. 2-tailed
4a. Hind wings present, usually large with one or more forked veins.
4b. Hind wings absent or small with two or three simple veins. If hind wing is present, the costal projection is long and straight or curved.
5a. Short, basally detached marginal intercalaries present between veins along entire outer margin of wings. Genital forceps of male with one short terminal segment.
5b. No true basally detached marginal intercalaries along outer margins of wings. Genital forceps of male with two or three short segments.
6a. Hind wings small or absent. Penes of male membranous. Upper portion of male eyes turbinate or raised on a stalk. Short, basally detached, single or double marginal intercalaries present in each interspace of forewings. Veins MA2 and MP2 detached basally from their respective stems.
6b. Hind wings relativly large. Penes of male well developed. Male eyes not turbinate. Marginal intercalaries attached basally to other veins. Veins MA2 and MP2 attached basally.
7a. Vein MA of forewings forming a more or less symmetrical fork. Veins MP2 and IMP extend less than 3/4 of the distance to the base of vein MP. Genital forceps of male two or three segmented. Thorax black or grey.
7b. Vein MA not as above. MA2 attached basally by a crossvein. Wing veins MP2 and IMP almost as long as vein MP and extend nearly to base. Genital forceps of male one-segmented. Thorax usually brown.


Waltz,RD; Burian,SK 2008 Ephemeroptera. In: An Introduction to the Aquatic Insects of North America. 4th ed. Eds: Merritt,RW; Cummins,KW; Berg,MB Kendall/Hunt Publishing Company, Dubuque, Iowa, 181-236.

Good Links

On this website:
Key to the Mayfly nymphs

Other Websites:
Digital Key to the Ephemeroptera of North Dakota http://www.waterbugkey.vcsu.edu/php/familykey.php?idnum=8&o=Ephemeroptera1L&type=family

Adult Mayfly Identification by Roger Rohrbeck http://www.hatchesmagazine.com/page/january2006/86

Brown, Wendy S. 2004 Mayflies (Ephemeroptera) of Gunnison County, Colorado, USA