Saskatchewan Stoneflies (Plecoptera)
Plecoptera larvae have some what flattened bodies, two segmented caudal tails and, in many, tufts of gills at the base of each leg and sometimes on the first two or three abdominal segments. Size can range from 5 mm to over 5 cm. The adults hold their two pairs of wings flat over their body and the caudal filaments are very much reduced.
The Plecoptera have a worldwide distribution. The North American fauna is made up of at least 550 species belonging to nine families. Eight families and 49 species have been reported from Saskatchewan.
In Saskatchewan, stoneflies are typically associated with cool streams and rivers. Some species have also been collected from cold northern lakes such as Lake Athabasca. Most species require high levels of oxygen and unpolluted conditions. This makes the stonefly community a valuable indicator of stream health.
The life cycle of stoneflies includes three stages: egg, larva, and adult. Adults usually have a life span of one to four weeks. The sexes in many species attract each other by drumming the tips of their abdomens on the substrate. Mating occurs while the partners are clinging to vegetation or on the ground. Females lay their eggs directly on the water surface or as they fly over the water. For most species the eggs hatch in three to four weeks.
The larvae require from a year to two or three years, depending on the species and habitat, to reach maturity. Larval diets range from other invertebrates (Perlidae and Perlodidae) to algae and detritus (Pteronarcyidae, Nemouridae, Capniidae). When the larvae are mature and ready to emerge they crawl out of the water onto a rock or other suitable substrate, such as a bridge pillar, where the adult emerges. Adults are poor fliers so they are usually found in close proximity to the larval habitat. In some cases the wings are reduced to non functional stumps, a condition called brachyptery.
In Saskatchewan, some members of the families Capniidae and Taeniopterygidae are referred to as "winter stoneflies". The larvae of these species develop through the winter and the adults emerge during ice break up in early spring.
Below is a larval key to the families of stoneflies found in Saskatchewan. The key is modified from Dosdall and Lehmkuhl (1979). The thumbnails below provide labelled diagrams of the general stonefly body and the mouth parts used as characters in the key.
1a: Gills present as branches on neck, or single or branched gills at leg bases.--2
1b: No gills present. --5
2a: Branched neck gills 
Arrow indicates neck gills. present.--Nemouridae
2b: No branched gills on neck. --3
3a: Single or branched gills present only on thorax. Sometimes there are subanal gills present. --4
3b: Gills on thorax as well as first two or three abdominal segments
Arrow indicates gills..--Pteronarcyidae
4a: Thoracic gills bushy
Arrow indicates gills..--Perlidae
4b: Thoracic gills are single
Arrow indicates gills..--Taeniopterygidae (In part)
5a: Paraglossa 
P = Paraglossa, G = Glossamuch longer than glossa.--6
5b: Paraglossa and glossa are about the same length
P = Paraglossa, G = Glossa.--7
6a: Mature larvae with hind wing pads strongly divergent. Cerci, when not broken, the same length or longer than abdomen. Maxillary palp segments evenly tapered. --Perlodidae
6b: Hind wing pads of mature larva parallel to body axis. Cerci only 3/4's the length of abdomen. Last maxillary palp segment much narrower and smaller than next to last segment.--Chloroperlidae
7a: Hind legs reaching to end of abdomen or longer. Wing pads in mature larvae divergent.--9
7b: Hind legs shorter 
~~~~~~~~~~~~ than abdomen. Hind wing pads parallel to body. (Capniidae and Leuctridae. These two families are difficult to separate except in good mature specimens.)--8
8a: Abdominal segments one to four split by a membranous section. Posterior segments not enlarged.--Leuctridae
8b: All nine abdominal segments split with a lateral membranous section. The posterior area of the abdomen slightly inflated.--Capniidae
9a: Second tarsal segment smaller than first tarsal segment.Nemouridae (In part.)
9b: Second tarsal segment similar in size to first tarsal segment.--Taeniopterygidae (In part.)
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Saskatchewan species list to Stoneflies (Plecoptera): List mostly from Dosdall and Lehmkuhl, 1987.
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References
Dosdall, L.M. 1992. New records of Saskatchewan stoneflies (Plecoptera) Proc. of the Entomol. Soc. of Manitoba. 48:14-31.
Dosdall, L. 1976. Saskatchewan Winter Stoneflies. Blue Jay 34:198-202.
Dosdall L.M. and D.M. Lehmkuhl. 1988. The nymph of Utacapnia trava (Nebeker and Gaufin) (Pleocptera:Capniidae) Pan-Pacific Ent. 64:353-357.
Dosdall, L.M. and D.M. Lehmkuhl. 1987. Stoneflies (Plecoptera) of the Lake Athabasca region of Northern Saskatchewan and their biogeographical affinities. Can. Ent. 119:1059-1061
Dosdall, L.M. and D.M. Lehmkuhl. 1979. Stoneflies (Plecoptera) of Saskatchewan. Queast. Ent. 15:3-116
Stark, B.P., S.W. Szcsytko and R.W. Baumann. 1986. North American stoneflies (Plecoptera): Systematics, distribution, and taxonomic references. Great Basin Nat. 46:383-397.
Stewart, K.W. and B.P. Stark. 2008. Chapter 14: Plecoptera. In. Merritt R.W. and K.W. Cummins. Ed. An Introduction to the Aquatic Insects of North America. 4th Edition. Kendall/Hunt Publishing Co. Dubuque, Iowa.
Stewart, K.W. and B.P. Stark. 1993. Nymphs of North American stonefly genera (Plecoptera). University of North Texas Press, Denton, Texas.