Click here for Stonefly checklist in the Great Smoky Mountains.
Plecoptera (stoneflies) are a small order of insects of about 2000 species worldwide,
with their long but fragmented fossil record dating back to the early Permian. The
living suborders, Arctoperlaria and Antarctoperlaria, easily contain the earliest
fossils. The more modern fossils are easily indentifiable from Miocene (38 - 54 MYA)
fossils. -- (University of Texas)
Stoneflies can be easily recognized by a few simple characters. They have three segmented
tarsi but their hind legs are not modified for jumping to the extent of Orthoptera (crickets
and grasshoppers). Their filiform antennae are at least half the length of the body. The
cerci are generally long as well, especially in the aquatic nymphs. The wings are almost
always present but are sometimes very short. They are folded horizontally back over the body.
These characters help distinguish them from Dermaptera and Embioptera which they superfically
resemble and to which they are probably closely related. The immatures are variously called
nymphs or naiads, but are most frequently referred to as nymphs. All nymphs are aquatic, and
resemble the adults in many respects. They also have three-segmented tarsi. The nymphs always
have long cerci and never a third central tail or median caudal filament. Gills, if they have
them, can occur on various parts of the thorax and abdomen and are composed only of filiments,
not plates.-- (University of Texas).
Antennae long, filiform
Body flattened, legs widely separated
Tracheal gills present as "tufts" behind the head, at base of legs, or around the anus
Each segment of thorax is covered by a large dorsal sclerite
Cerci long, multi-segmented
Antennae long, filiform
Front wings long and narrow; M-Cu crossveins form distinctive boxes near center of front wing
Hind wings shorter than front wings; basal area of hind wing enlarged and pleated
The name Plecoptera, refering to the pleated hind wings which fold under the front wings
when the insect is at rest, is derived from the Greek "pleco" meaning folded and "ptera"
meaning wing. -- (N.C.
State University Entomology Dept.)
Stoneflies probably represent an evolutionary "dead end" that diverged well over 300
million years ago and are regarded as the earliest group of Neoptera. Immature stoneflies
are aquatic nymphs (naiads) that usually live under stones in fast-moving, well-aerated
water. Oxygen diffuses through the exoskeleton or into tracheal gills located on the thorax,
behind the head, or around the anus. Most species are herbivorous, feeding on algae and
other submerged vegetation, but two families (Perlidae and Chloroperlidae) are predators
of mayfly nymphs (Ephemeroptera) and other small aquatic insects. Adult stoneflies emerge
from their streams and can generally be found on the banks next to their previous habitat.
They are not active fliers and usually remain near the ground where they feed on algae or
lichens. In many species, the adults are short-lived and do not have functional mouthparts.
Stoneflies are most abundant in cool, temperate climates. --
(University of Texas)
Stoneflies require cool, well-oxygenated water for their nymphal development and are
therefore very susceptible to human abuse of water courses. Farm drainage, land
clearing, impoundment of water courses all of which cause changes in temperature and
substrate content can eliminate stoneflies from a habitat. --
(University of Texas).
Because of stoneflies' impact susceptibility, they are used by ecologists as indicators
of water purity. Stoneflies are also an important source of food for game fish (e.g., trout
and bass) in cold mountain streams.--
(N.C. State University Entomology Dept.)
With a few exceptions in the southern hemisphere living on damp soil, stonefly nymphs
dwell in aquatic habitats. The preferred habitat is rocky streams with at least a
noticeable current. Some species can live in damp sandy areas. Although we know
much less about lakes as habitats than rivers and streams, lakes can provide suitable
habitat in the north and at high latitudes.The usual habitat in running water contains
rocky, stony, or gravel substrata with more diversity in cooler, swifter water. Some
studies have shown a correlation between certain species and certain habitats. For
instance, Perlidae and Perlodidae are usually encountered under large stones, while
Chloroperlidae tend to occur in gravel and Pteronarcyidae are frequently found in leaf
packs.-- (University of Texas).
Stoneflies usually spend 10 months to 2 years living and growing as larvae in the water. When ready the larvae emerge from the water and transform into terrestrial adults.
There are 9 different families of stoneflies in North America.
Most kinds of stoneflies have 2 long cerci (tails) and 2 tarsal claws (nails) at the end of each leg.
Habitat & Feeding
Stoneflies can be found in most running waters and are commonly found in boulder, cobble, water-soaked wood, and leaf packs. Most species are predators or shredders (eat decaying plant material).
Water quality indicator status
Stoneflies are usually associated with clean, cool flowing streams. Most stonefly
are sensitive to water pollution. Generally the presence of stoneflies is a reliable indicator of excellent water quality, but because of their specific habitat requirements, their absence does not necessarily mean the waterbody is polluted. Stonefly larvae are part of the widely used EPT Index (Ephemeroptera-Plectoptera-Trichoptera) to measure water quality condition. It is the number of different taxa of mayflies, stoneflies, and caddisflies.
In low oxygen conditions, larvae will do "push-ups" to move water across their gills.
One species, when the aquatic larva is pursued by a predator, will reflex bleed. They squeeze out drops of their blood; scientists think that this produces a bad smell or taste or is done to confuse the attacker.