Superkingdom Eukaryota
Kingdom Animalia
Phylum Arthropoda
Superclass Hexapoda
Class Insecta
Subclass Pterygota
Series Neoptera
Order Plecoptera

Common name(s): Stonefly

Description: Medium in size, from 12 mm to 65 mm. At rest, wings partly wrap the abdomen and extend beyond the abdominal apex, but wing reduction is frequent. Legs are weak. Prognathous mouthparts. The abdomen is soft, with filamentous cerci. Antennae are filiform. The stonefly has bulging compound eyes and two or three ocelli. The thorasic segments are subequal and the fore and hind wings are membranous. Immature nymph stages closely resemble adults.

Fun facts: Plecoptera are a minor and often cryptic order of 16 families, and perhaps 2000 species worldwide, most often in temperate and cool areas. They are hemimetabolous with the adults resembling winged nymphs. The abdomen is 10-segmented, with vestiges of segments 11 and 12 serving as paraprocts, cerci and epiproct, a combination of which serve as male accessory copulation structures.

Nymphs have 12-24, perhaps as many as 33, aquatic instars; wing pads are first visible in half-grown nymphs. The nymph's tracheal system is closed, with simple or plumose gills on the basal abdominal segments or near the anus - sometimes extruded through the anus (that's right, anal gills) or on the mouthparts, neck or thorax, or even lacking altogether. The cerci are multi-segmented and there is no median terminal filament.

Most North American species are univoltine, but maturation may take up to four years, at which time nymphs will leave the water and molt upon nearby vegetation. Eggs are dropped on water, laid in jelly on water, or laid underneath stones in water or in damp crevices near water. Water is essential for the development of these insects, and this is a barrier to their colonization of a larger area. Nymphs occur predominantly on stony or gravely substrates in cool water, mostly well-aerated streams, less often in lakes. Stoneflies are very intolerant of organic and thermal pollution in water.

Nymphs may be omnivores, detritivores, herbivores or predators. Adults feed on algae, lichen, cellulose plants and rotting wood. There are some species in which the adults do not eat; they mate and die (on stored energy from the nymph stage).

Plecoptera are thought to have a relationship with the Orthopteroid-Plecopteroid assemblage, as can be seen on the Insect Phylogenetic Tree.

sourced, in part, by The Insects: An outline of entomology, second ed. Gullan, P.J. and P.S. Cranston. Blackwell Science, Great Britain, 2000.

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