Stream Bugs: Mayflies

Local Streams

You can see mayflies and other stream bugs up close this summer by volunteering to help gather samples from one of 20 streams that Stream Team monitors throughout Thurston County.

Stream Bugs: Up Close and Personal

We all know that fish live in streams, but have you ever wondered what else lives beneath the water? Here in the Pacific Northwest, we have many different types of “stream bugs” that live on or below the gravel in the streams. These critters, known as benthic macroinvertebrates, include many different types of insect larvae and nymphs such as stoneflies, true flies and mosquitoes. Crayfish, freshwater mussels, aquatic worms and spiders, and snails are also benthic macroinvertebrates.

When studying these critters, scientists found that some are highly sensitive to pollution in streams while others are more tolerant to pollution and habitat disturbance. For this reason, “stream bugs” are monitored, collected and used as indicators of stream health.

Are you curious about benthic macroinvertebrates and how they survive in an underwater world? You can get a chance to see these macroinvertebrates up close by volunteering to collect “stream bug” samples with Stream Team this summer. If you can’t wait until summer, here is a sneak preview of what you might see when you go out to a stream to monitor.

Mayfly nymph

Local Streams This is a mayfly nymph, which is an immature or larval form of a mayfly. Most mayflies are highly sensitive to water quality. They breathe through tiny gills located on the sides of their abdomen. Thus, they need cool, clean water with plenty of dissolved oxygen.

Their gills can get clogged by sediment (dirt), so they are usually not found in streams that experience high rates of flooding or erosion. This is why trees growing alongside a stream are so important. Their roots help bind the soil, thereby slowing erosion, while their branches and leaves help shade the stream. Cool water holds more dissolved oxygen, which mayflies, salmon and many other stream critters need to survive. Once the mayfly matures, it will swim to the top of the water and shed its outer layer so that it can spread its wings.

Mayfly adult

Local Streams The scientific name for a mayfly is Ephemeroptera, the root of which is “ephemeral” meaning “shortlived.” This is a fitting name as mature mayflies only live for approximately 24 hours. In this short amount of time, they manage to find a mate, lay eggs and ensure the mayfly lifecycle continues. The female lays the eggs in or near the water. Once they hatch, the larvae spend several months to a year in the stream before they mature. Mayflies are a favored food for salmon, so fishermen pay close attention to mayfly hatches as salmon seem to “fly” at the chance to dine on them.

You can see mayflies and other stream bugs up close this summer by volunteering to help gather samples from one of 20 streams that Stream Team monitors throughout Thurston County.

No experience is necessary to join the Stream Team monitoring group. Simply attend one evening training to learn how and why Stream Team monitors benthic macroinvertebrates. Then, sign up to monitor one or more streams later in the summer. Monitoring usually takes three to five hours, depending on the stream. Monitoring takes place on weekdays, evenings and weekends to help accommodate busy schedules.

To find out more about benthic macroinvertebrate monitoring with Stream Team, or to register for a training, contact Ann Marie at pearcea@co.thurston.wa.us or 360-754-3355 ext. 6857.