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.

Why are Macroinvertebrates Important?
Macroinvertebrate Sampling
Macroinvertebrates are relatively easy to collect. They are found on rocks, woody debris, and stream sediments within the creek. To collect them, however, you need a fishing license and a collector's permit. Please visit http://www.fish.state.pa.us/education/collinfo.htm for more information on obtaining the appropriate permit.
Macroinvertebrates Role in Water Quality

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

SCCA volunteers conduct macroinvertebrate sampling occasionally at their stream sampling sites to gain a picture of changes in water quality seasonally or from year to year. Check back soon for macroinvertebrate sampling results in our watershed! SCCA has done many educational programs about macros over the years...some of the locations or events that included a SCCA macro demonstration are Amish & Mennonite schools in Blain, Susquenita Elementary Earth Day, Kids Creek Day event at Carroll Township Park as well as the County Envirothon.

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.

Virginia Save Our Streams (based on the methods from the Isaac Walton League of America)


Stroud Water Research Center

EPA Biological Indicators of Watershed Health