STONEFLIES

Stoneflies are insects in the order Plecoptera.  The name Plecoptera means “braided wing” which refers to the pattern of veins in the wings of adults.   The common name “stonefly” refers to the occurrence of the naiads on the rocks of streams.  These insects spend their youth in well oxygenated streams where they often feed on the film of bacteria, algae, and fungi that grow on rocks.  They may exist in the naiad stage for one to four years, depending upon the species.  As they mature, they molt until their final molt which forms a flying adult.  The adult life stage is short-lived (a few weeks) and many species of adults don’t even feed.  The adults can be found in swarms, where they mate.  The female will fly over the water and drop her eggs which will hatch in the water and continue the life cycle.  Swarming is a good thing.  When there are massive amounts of individuals out at the same time, your individual chance of being eaten by a predator decline.  Plus, you theoretically have more potential mates to pick from.  Benefit! 

So, lets circle back to the fact that these insects are found in well oxygenated streams.  Stoneflies have fluffy gills under their arm pits.  When oxygen levels are low, they will do push-ups to get more oxygen in the water to flow over the gills.  They are sensitive to oxygen levels and will leave or die in areas that are unsuitable.  As a result of this sensitivity, they are good indicators of stream health.  We call them “bioindicators”.

As it turns out, stoneflies are tasty little crumpets.  Fly fisherpersons spend countless hours making fishing lures (flies) that look like stoneflies.  Because the adults swarm, fisherpersons are most successful if they can “match the hatch” which means they are using a fly that looks like the species that is swarming.