Saskatchewan Stoneflies (Plecoptera)
The Plecoptera have a worldwide distribution. The North American fauna is made up of about 550 species belonging to nine families. Eight families and at least 49 species have been reported from Saskatchewan.
Plecoptera larvae have somewhat flattened bodies. Many segemented antennae and two multi-segmented tails (cerci). Some larvae have tufts of gills at the base of each leg and/or 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, almost flying ant like, and the caudal filaments are very much reduced.
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 one to two or even three years to develop. The development time depends on the species and habitat. 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.
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 through fissues in the ice during 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).
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 present.--Some 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 present on thorax and first two or three abdominal segments.--Pteronarcyidae
4a: Thoracic gills bushy.--Perlidae
4b: Thoracic gills are single.--Some Taeniopterygidae
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
8b: All nine abdominal segments split with a lateral membranous section. The posterior area of the abdomen slightly inflated.--Capniidae
9b: Second tarsal segment similar in size to first tarsal segment.--Some Taeniopterygidae
Dosdall, L. M. and D. J. Giberson. 2014. Stoneflies (Plecoptera) of the Canadian Prairie Provinces. In Arthropods of Canadian Grasslands (Volume 3): Biodiversity and Systematics Part 1. Edited by H. A.Cárcamo and D. J. Giberson. Biological Survey of Canada. pp. 201-229. © 2014 Biological Survey of Canada. ISBN 978-0-9689321-6-2 doi: http://dx.doi.org/10.3752/9780968932162.ch7 Species checklist available at http://dx.doi.org/10.5886/gaqds797
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