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Ephemeroptera: Baetidae of Gunnison County, Colorado

Small Minnow Mayflies
Nymph key to genera

BugLab's Western Baetidae Nymph key

The "easy" ones are first.
Very under construction, Updated 29 Oct 2008
1a. One or more pairs of gills with recurved posterior and ventral flap.

Common in beaver ponds and permanent ponds. Sometimes found in slow parts of streams.

1b. Dense row of long fine setae on the back (or dorsum) of the legs.

1c. Everyone else. All gills are flat plates. No rows of setae on the legs. May or may not have hind wingpads.

2a. Tails banded at the apex of every third to fifth segment. Rare.

Gill trachae asymmetrical with most branches on median side; labrum with small median notch along anterior margin and apex of labial palpi simple and truncate.

Rare, high altitude, found in Tomichi Creek.

2b. Tails unbanded or rarely banded in a different pattern.

Apex of labial palp variable, not straight edged; gill trachea also variable;

3a.Right or both mandibles with a tuft of setae between the incisors and the prosthecae.

Villopore absent.

3b. Neither mandible with a tuft of setae between the incisors and the prosthecae.

Villopore present. (must have mature nymphs with large wingpads to see this!) 2 or 3 tailed with the middle tail subequal to other tails or shorter.

4a. Gills missing from abdominal segment one. Gills on segments two to seven.

3-tailed with tails subequal in length. Keel on head between antennae. Alive they are small and dark compared to the other genera keyed here.

4b. Gills present on segments one to seven. Rare.

5a. Three tailed with hind wingpads present. Very Common.
Baetis spp. in part

5b. Two tailed, possibly with very short stub of center tail. With or without hind wingpads.

6a. Hind wing pads absent.
6b. Hind wing pads present.
Baetis spp. in part

Good Links

On this website:
Introduction to Baetidae
Key to Baetidae adults

Other Websites:


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.      Very useful. They summarized all of the following papers nicely on pages 86-88.

McCafferty,WP; Waltz,RD 1990 Revisionary synopsis of the Baetidae (Ephemeroptera) of North and Central America. Transactions of American Entomological Society 116, 769-799.

Morihara,DK; McCafferty,WP 1979 The Baetis larvae of North America (Ephemeroptera:Baetidae). Transactions of American Entomological Society 105, 139-221.

Wang,TQ; McCafferty,WP 1996 New diagnostic characters for the mayfly family Baetidae (Ephemeroptera). Entomological News 107 2, 207-212.

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