Stoneflies

(Plecoptera)

Background
Development
Characteristics
Importance

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Background:

Stoneflies get their name because winded adults are often found resting on stones. Immature stoneflies can be found under rocks where water is allowed to flow through their gills allowing them to breathe. As adults, they are terrestrial.

Development:
EGGS
Some female stoneflies will skim the surface of the stream just so that their abdomens touch the water and release their eggs. Others will crawl to the bottom of the stream and release their eggs onto substrates. Stoneflies can often be seen laying their eggs on the water, as they are not very good fliers and usually cause quite a disturbance in the process. Eggs may take a few weeks to hatch, or a few months in some species.
NYMPH
Depending on the species, the nymph stage may last up to 3 years. They may go through 10 to 30 moltings. Since they do not go through a pupa stage, they are considered to have incomplete metamorphosis.
ADULT
When the nymph is ready, it will crawl out of the stream onto a hard substrate. It will remain there until it is dry so that its nymphal case can split. The adult will emerge from the case looking just like the nymph, only with wings. Some adults do not have wings and some have shortened wings, none are very good at flying. It will then fly or climb to nearby trees. As soon as possible, they will mate. The males attract females by drumming their abdomens on a tree branch. Stoneflies can live from 1 to 7 weeks, depending on the species.
Characteristics:
Immature stoneflies
•Long antennae
•Flat body
•Widely separated legs
•Gills behind the head, legs, and around anus

Adults
•Long antennae
•Long and narrow front wings
•Shorter hind wings

Importance:
Stoneflies can be useful tools in studies of historical biogeography because they cannot fly very well. This means that they cannot cross certain topographic boundaries. They are also signs of good water quality because nymphal development requires well-oxygenated water. Sewage, drainage, and land clearing can all cause changes in the temperature and substrate content of the stream, which can eliminate stoneflies from the habitat. Along with the caddis fly and the mayfly, fishermen also use stoneflies as bait or as simulated wet or dry flies. They are also a source of food for trout in the creek.
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