What is a Macroinvertebrate?
"Invertebrate" means without a backbone and "Macro" means large – able to be seen without the use of a microscope. Common stream macroinvertebrates include mayflies, stoneflies, caddisflies, mussels, crayfish, and snails.
Macroinvertebrates are important in the aquatic food chain – fish food, which also makes them important to fly-fisherman. But they are also great indicators of stream water quality. In fact, where a water sample can give you a snapshot view of water quality and fish can escape from small amounts of pollution – macroinvertebrates can provide information about pollution that is not present at the time of sample collection. The type of macroinvertebrates present can even indicate the type of pollution that has occurred in the past.
Indicators of Good Water Quality – most mayflies, stoneflies, caddisflies, planaria, gilled snail, water penny, and hellagramite.
Indicators of Good or Fair Water Quality – most crayfish, alderflies, craneflies, sowbugs, damselflies, scuds, dragonflies, and mussels.
Indicators of Poor Water Quality – most leeches, lunged snails, aquatic worms, and black flies.
The absence of good water quality indicator species can tell you that you may have a pollution problem. An easy test of water quality is to count the number of mayflies, stoneflies, and caddisflies in your sample. This is also called the EPT taxa index, named after their scientific names. The higher the EPT score, the better quality stream you are sampling.
Macroinvertebrates in the Shermans Creek Watershed
Want to Know More?
Here are some great links on using macroinvertebrates as water quality indicators and links to help you identify macroinvertebrates you found in your creek.