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Order Plecoptera - The Stoneflies
Common Stonefly larvae Giant Stonefly larvae Perlodid Stonefly larvae
The stoneflies are an interesting group of insects with all species having aquatic larvae. Their presence usually represents good water quality, since the majority of the species need highly oxygenated water. Any type of organic enrichment, which usually leads to lower dissolved oxygen levels, can prohibit their occurrence. Unfortunately, North Dakota rivers and streams often have medium to high levels of organic material and therefore this group is not widespread in the state.

General Life cycle - Stoneflies undergo incomplete metamorphosis. This means there is a distinct larval stage, usually called nymphs or naiads, and a distinct adult stage but no intermediate pupal stage. The nymphs are aquatic and the adults are winged, terrestrial insects. Nymphs will develop from several months up to three years in their aquatic environment before molting into adults. When they are ready to make the transition from nymph to adult, the nymphs will crawl out of the water and begin the process of ecdysis in which the adult will exit the old nymphal exoskeleton. Stonefly adults will emerge at almost any time of year, there are even species that emerge during the winter months.

Identification - At first glance, stonefly larvae are similar in appearance to mayflies. However, closer examination reveals several noticeable differences. Stoneflies usually have two caudal filaments and mayflies usually have three. The gills of mayflies are restricted mainly to the abdomen whereas stoneflies can have gills on their thorax, mouthparts, leg bases, as well as their abdomen. The mayflies have one tarsal claw on the tip of their legs whereas the stoneflies have two.

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