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Plecoptera of Gunnison County, Colorado
Nymph Key to Family

Updated 14 Feb 2005

1a. Abdomen or thorax with branched gills.

(Visible on very small nymphs with a microscope and on medium to large nymphs in the field. At a glance these nymphs appear to have hairy armpits.)

Pteronarcys californica belly
1b. Abdomen or thorax without branched gills.

Animals with a few single gills or only gills around the neck belong here.


2a. Abdomen with finely branched gills on first two or three segments.
Family Pteronarcyidae

Mature nymphs are big, dark and prehistoric looking.


2b. Only the thorax has branched gills.

Nymphs have handsome brown and yellow patterns on their heads and thorax.


3a. Paraglossae and glossae about equal length.

(You must have a microscope to see this, flip the nymph on its back and look at it's mouthparts)

Pteronarcys californica underside of face
3b. Paraglossae much longer than glossae.
4a. Large triangular plate at the end of the dorsal side of the abdomen. Telescoping finger like gills on the coxae or leg segment closest to the body. Second tarsal segment as long as or longer than the first.

The coxal gills may be hard to see on small or poorly preserved stoneflies. Seeing the long second tarsal segment can be subtle too.

4b. Second tarsal segment shorter than the first

(Most nymphs in the county are here)

5a. Robust, hairy nymphs
Metathoracic wing pads divergent in mature nymphs
Cervical gills present or absent.
5b. Elongate, almost hairless nymphs,
Inner margin of metathoracic wingpads nearly parallel in mature nymphs
No setae or if setae are present they're restricted to short hairs

6a. Sterna and terga of all abdominal segments separated laterally by a membranous fold
Sometimes have striking markings.
Inner margins of hind wing pads have a notch on the anterior third.

6b. First 7 or fewer abdominal segments divided laterally by a membranous fold, sterna and terga fused on the remaining segments forming a continuous ring
Body very elongate.
Inner margins of hind wing pads have a notch on the posterior third.

7a. Terminal segment of maxillary palp much thinner than preceding segment
Inner margin of metathoracic wingpads nearly parallel in mature nymphs
Cerci 3/4 or less than the length of the abdomen. (short-tailed)

7b. Terminal segment of maxillary palp slightly thinner than preceding segment
Inner margin of metathoracic wingpads divergent in mature nymphs
Cerci longer than abdomen. (long-tailed)

References

Keys and illustrations modified from the following:
Baumann,RW, Gaufin,AR and Surdick,RF 1977 The stoneflies (Plecoptera) of the Rocky Mountains. Memoirs of the American Entomological Society 31, 1-208.

Stewart,KW; Harper,PP 1996: Plecoptera. In: An Introduction to the Aquatic Insects of North America. 3rd ed. Eds: Merritt,RW; Cummins,KW Kendall/Hunt Publishing Company, Dubuque, Iowa, 217-266. Buy from Amazon.com

Stewart,KW and Stark,BP 2002: Nymphs of North American Stonefly Genera. 2nd edition The Caddis Press, Columbus, Ohio. 510 pages.

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. Buy from Amazon.com

Brown, Wendy S. 2004 Key to the Aquatic Insects of Gunnison County, Colorado
www.gunnisoninsects.org