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Ephemeroptera: Baetidae of Gunnison County, Colorado

Draft key to Genera
for
Blue Winged Olives (Adult Small Minnow Mayflies)

Very Under Construction! Updated 30 Oct 2008

Some of these species are among the smallest and most delicate mayfly adults in our area. This key is for imagos, which have clear wings. The subimagos or duns need to molt one more time to become sexually mature. Their wings are blue or grey, hence one of their common names Blue-winged Olive (BWO). To help identify these bugs, look for colors and patterns on the mayflies you're enjoying, sometimes they fade after death or preservation.

1a. Brown pattern on leading edge of forewings. Hind wings with blunt costal projection and 10 more crossveins. Abdomen with dark spots.

Common around beaver ponds for most of the summer.

1b. Forewings clear, without pattern. Hind wings present or absent, if present with less than 6 veins; costal projection of hind wings pointed, hooked or absent. Abdomen variable, rarely with spots.

2a. Marginal intercalaries of forewings occur singly. Hind wings present or absent, if present hind wings with costal projection hooked or recurved.

Not confirmed in Gunnison County, possibly present.

2b. Marginal intercalaries of forewings occur in pairs. Hind wings present or absent, if present costal projection of hind wings variable, rarely hooked.

3a. Anterior processes of mesothorax coniform, projecting dorsally; hind wings present or absent, if present hind wings without costal processes.
3b. Anterior processes of mesothorax not coniform and not projecting dorsally; hind wings, when present, with or without a costal process.

4a. Hind wings without costal process or with greatly reduced costal process. Hind wings present. Distinct plate between forcep bases. Terminal segment of forceps small and rounded. Lower elevations.

Not confirmed in Gunnison County, possibly present.
Pseudocloeon propinquum

4b. Hind wings present or absent, if present hind wings with costal process.

5a. Hind wings with costal process hooked. Terminal segment of male forceps elongate. Bilobed process present between forcep bases.
5b. Hind wings present or absent, if present, costal process rarely hooked. Terminal segment of male forceps variable. No bilobed processes between forceps bases.

6a. Hind wings with second longitudinal vein forked, vertex of fork proximal and toward wing base. Terminal segment of male forceps elongate.
6b. Hind wings present or absent, if present hind wings with second vein simple, or if forked, vertex of fork occurs distally beyond middle of hind wing.

7a. Hind wings present.
Baetis in part

7b. Hind wings absent or if present small, slender, with only 2 longitudinal veins.

8a. Forceps of male strongly curved. Abdominal terga 3 and 4 strongly pigmented in red medially. Terga 5 and 6 washed in red. Rectangular plate present between forceps bases.
8b. Forceps of male not strongly curved as above. Abdominal terga not pigmented as above. Rectangular plate between forceps bases absent except for fuscatus group.
Baetis in part

References

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.
     The almost dichotomous key on this web page was copied and altered from the adult mayfly key in this book.

Good Links

Key to Baetidae larvae
Key to the Adult Mayflies
Brown, Wendy S. 2004 Mayflies (Ephemeroptera) of Gunnison County, Colorado, USA
www.gunnisoninsects.org