Plecoptera is an

order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...

insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...

s commonly known as stoneflies. Some 3,500 species are described worldwide, with new species still being discovered. Stoneflies are found worldwide, except Antarctica. Stoneflies are believed to be one of the most primitive groups of

Neoptera Neoptera (Ancient Greek ''néos'' ("new") + ''pterón'' ("wing")) is a classification group that includes most orders of the winged insects, specifically those that can flex their wings over their abdomens. This is in contrast with the more basa ...

, with close relatives identified from the

Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...

and Lower

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...

geological periods, while true stoneflies are known from fossils only a bit younger. Their modern diversity, however, apparently is of

Mesozoic The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...

origin. Plecoptera are found in both the Southern and

Northern Hemisphere The Northern Hemisphere is the half of Earth that is north of the equator. For other planets in the Solar System, north is defined by humans as being in the same celestial sphere, celestial hemisphere relative to the invariable plane of the Solar ...

s, and the populations are quite distinct, although the

evolution Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...

ary evidence suggests species may have crossed the

equator The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...

on a number of occasions before once again becoming geographically isolated. All species of Plecoptera are intolerant of

water pollution Water pollution (or aquatic pollution) is the contamination of Body of water, water bodies, with a negative impact on their uses. It is usually a result of human activities. Water bodies include lakes, rivers, oceans, aquifers, reservoirs and ...

, and the presence of their

nymph A nymph (; ; sometimes spelled nymphe) is a minor female nature deity in ancient Greek folklore. Distinct from other Greek goddesses, nymphs are generally regarded as personifications of nature; they are typically tied to a specific place, land ...

s in a stream or still water is usually an indicator of good or excellent water quality.

Description and ecology

Stoneflies have a generalized anatomy, with few specialized features compared to other insects. They have simple mouthparts with chewing mandibles, long, multiple-segmented antennae, large

compound eye A compound eye is a Eye, visual organ found in arthropods such as insects and crustaceans. It may consist of thousands of ommatidium, ommatidia, which are tiny independent photoreception units that consist of a cornea, lens (anatomy), lens, and p ...

s, and two or three

ocelli A simple eye or ocellus (sometimes called a pigment pit) is a form of eye or an optical arrangement which has a single lens without the sort of elaborate retina that occurs in most vertebrates. These eyes are called "simple" to distinguish the ...

. The legs are robust, with each ending in two claws. The

abdomen The abdomen (colloquially called the gut, belly, tummy, midriff, tucky, or stomach) is the front part of the torso between the thorax (chest) and pelvis in humans and in other vertebrates. The area occupied by the abdomen is called the abdominal ...

is relatively soft, and may include remnants of the nymphal gills even in the adult. Both

s and adults have long, paired cerci projecting from the tip of their abdomens. The name "Plecoptera" literally means "

braid A braid (also referred to as a plait; ) is a complex structure or pattern formed by interlacing three or more strands of flexible material such as textile yarns, wire, or hair. The simplest and most common version is a flat, solid, three-strand ...

ed-wings", from the

Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

''plekein'' (πλέκειν, "to braid") and ''pteryx'' (πτέρυξ, "wing"). This refers to the complex venation of their two pairs of wings, which are membranous and fold flat over their backs. Stoneflies are generally not strong fliers, and some species are entirely wingless. A few wingless species, such as the Lake Tahoe benthic stonefly ('' "Capnia" lacustra'') or '' Baikaloperla'', are the only known insects, perhaps with the exception of ''

Halobates ''Halobates'', colloquially the sea skaters or ocean striders, are a genus with over 40 species of water striders. Most ''Halobates'' species are coastal and typically found in sheltered, coastal marine habitats (a habitat where a few other g ...

'', that are exclusively aquatic from birth to death. Some

true water bug Nepomorpha is an infraorder of insects in the "true bug" order (Hemiptera). They belong to the "typical" bugs of the suborder Heteroptera. Due to their aquatic habits, these animals are known as true water bugs. They occur all over the world ou ...

s (Nepomorpha) may also be fully aquatic for their entire lives, but can leave the water to travel. The nymphs (technically, "naiads") are aquatic and live in the

benthic zone The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from the Ancient Greek word (), meaning "the depths". ...

of well-oxygenated lakes and streams. A few species found in New Zealand and nearby islands have terrestrial nymphs, but even these inhabit only very moist environments. The nymphs physically resemble wingless adults, but often have external gills, which may be present on almost any part of the body. Nymphs can acquire oxygen via diffusing through the exoskeleton, or through gills located on behind the head, on the thorax, or around the anus. Due to their nymph's requirement for well oxygenated water, the species is very sensitive to water pollution. This makes them important indicators for water quality. Most species are herbivorous as nymphs, feeding on submerged leaves and benthic algae, but many are hunters of other aquatic arthropods.

Life cycle

The female can lay up to one thousand eggs. It will fly over the water and drop the eggs in the water. It also may hang on a rock or branch. Eggs are covered in a sticky coating which allows them to adhere to rocks without being swept away by swift currents. The eggs typically take two to three weeks to hatch, but some species undergo

diapause In animal dormancy, diapause is the delay in development in response to regular and recurring periods of adverse environmental conditions.Tauber, M.J., Tauber, C.A., Masaki, S. (1986) ''Seasonal Adaptations of Insects''. Oxford University Press It ...

, with the eggs remaining dormant throughout a dry season, and hatching only when conditions are suitable. The insects remain in the nymphal form for one to four years, depending on species, and undergo from 12 to 36 molts before emerging and becoming terrestrial as adults. Before becoming adults, nymphs will leave the water, attach to a fixed surface and molt one last time. The adults generally only survive for a few weeks, and emerge only during specific times of the year when resources are optimal. Some do not feed at all, but those that do are herbivorous. Adults are not strong fliers and generally stay near the stream or lake they hatched from.

Phylogeny

A summary of the phylogeny of stoneflies is shown below. While the Antarctoperlaria, Arctoperlaria, Euholognatha, Systellognatha are well supported, several further relationships are disputed. Some families have only been analyzed by one study (indicated by dashed lines) and their placement may change in the near future.

Notes

References

External links

* * * Plecoptera Species File
order Plecoptera (Version 5.0/5.0)
{{DEFAULTSORT:Plecoptera Insect orders Extant Permian first appearances Taxa named by Hermann Burmeister Symbols of Delaware Aquatic insects Polyneoptera