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stonefly

 

Plecoptera (stoneflies)

Plecoptera Order Description

The Order Plecoptera consists of the insects that are commonly referred to as stoneflies. Plecoptera are the most sensitive order of aquatic insects.  Consequently, stoneflies are often restricted to habitats where there is little human development, clear water, and high dissolved oxygen content.  Stoneflies are often found in fast moving streams and rivers where there the substrate is covered in cobblestone or woody plant debris.


Plecoptera Families:
Click on each to display information below .

 

CapniidaeFamily Capniidae

Small winter stoneflies

As their common name implies, these stoneflies are most common during the winter months. Capniid adults emerge in the winter, and their conspicuously black bodies can easily be seen against the white snow background. Capniid larvae are most commonly found in small streams and rivers. They are specifically located in the gravel and detritus of fast moving streams where there is accumulation of gravel and organic matter. The larvae are small; the average body length is 5 to 10 mm. The abdominal segments are separated by abdominal folds.

Plecoptera Life History
Larval
Eggs and larvae of all stoneflies in North America are aquatic. Stonefly larvae are extremely sensitive to water quality, especially dissolved oxygen content. Each species of Plecoptera has specific requirements for water temperature, stream size, and substrate type. The larval stage may last from 1 to 3 years depending on the species. Embryonic and larval development continues throughout the winter months, but growth rate may be decreased during this time. In some species that inhabit areas of extreme seasonal temperature change embryonic development may be halted until environmental conditions are more favorable. Larvae of these species must grow very rapidly during the remaining months in order to fully develop within one year.

In general, Plecoptera larvae have two caudal filaments, or tails protruding from the abdomen. There are two tarsal claws at the end of each leg. Gills may be present on either the thorax or on the abdominal segments. Wings appear as small buds on the thorax of stonefly larvae. These buds will grow in size with each succession molting, or shedding of the exoskeleton.

Adult
The adult life stage is completely terrestrial. Most Plecoptera spend their adult life near riparian vegetation or on rocks near the stream that they emerged from. When a larval stonefly is ready to emerge as an adult it will crawl out of the water and shed its exoskeleton. Stonefly larvae emerge into adults throughout the year based on the individual family’s life cycle. The adult stage is considerably shorter than that of the larval stage; most adults live for only 1 to 4 weeks.  In most Plecoptera families, the adult male and female are attracted to each other by drumming. A stonefly drums by tapping its abdomen on the river-bottom. Male stoneflies continue drumming throughout their adult life, but only virgin females will respond to the call. Both the male and female will move towards the sound of the other’s drumming until they are in contact and mating can occur. The adults possess wings, but they are not active fliers.

Feeding habits
The food eaten by Plecoptera larvae varies between species, developmental stage, and the time of day. Most developing larvae will feed on plant material and detritus (dead organic material) during the first few instars, or stages, while larvae in the later instars usually feed on other animals in addition to plant materials. Most adult stoneflies do not have functioning mouthparts and they do not eat during the adult stage.

Ecological importance

Plecoptera are a source of food for many game fish. Population levels of Plecoptera are also used as biological indicators of water quality. Stoneflies are very sensitive to water quality, especially dissolved oxygen levels, thus deteriorating populations of stoneflies may mean that poor water quality threatens the health of the aquatic ecosystem.

 


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