Freshwater Macroinvertebrates

from Streams in Western Washington and Western Oregon

Macroinvertebrate Resources | Know Your Macros (downloadable PowerPoint slideshow)



Most recent additions: October 2015 (note: these images may not show in the links listed below)

Instructions: For a larger view of the specimens below, click on an image. A new window will appear with an enlarged picture of the organism. Close the window when you are through looking at the image. For more information and additional pictures of the macros (or similar organisms), click on the links next to the images. Information on size, location, and date of collection for many of the organisms can be found on these supplemental pages.*

Phyla: Cnidarians, Platyhelminthes, Annelids & Mollusks

Phylum: Cnidarians


Phylum: Platyhelminthes


Phylum: Annelida
(segmented worms)


Phylum: Mollusca

Phylum: Arthropoda

Class: Arachnida


Class: Crustacea


Class: Insecta
Order: Coleoptera


Class: Insecta
Order: Ephemeroptera


Class: Insecta
Order: Diptera
(true flies)


Diptera (Continued)


Class: Insecta
Order: Hemiptera
(true bugs)


Class: Insecta
Order: Lepidoptera
(aquatic caterpillars)

macro - 54

Class: Insecta
Order: Megaloptera


Class: Insecta
Order: Odonata


Class: Insecta
Order: Plecoptera


Plecoptera (continued)


Class: Insecta
Order: Tricoptera


Tricoptera (continued)

Other or Unknown Macros

Other/Unknown Macros

Phylum: Chordata

Class: Osteichthyes
(Bony Fish)


Class: Amphibia


* Some of the supplemental pages provide pollution tolerance levels for organisms used in biomonitoring. The tolerance levels are generally described as: tolerant of pollution; moderate (somewhat sensitive), or sensitive (intolerant of pollution). While tolerance levels can actually vary by species, and different species can have varying tolerances to specific pollutants, the levels given are generalized for the family of organism. (Flathead mayflies, for example, are considered to have a moderate tolerance to pollution. Some species of flathead mayflies, however, are sensitive, while others are tolerant.) In describing the tolerance levels for the various macros, I relied on information presented in Macroinvertebrates of the Pacific Northwest, A Field Guide by Jeff Adams and Mace Vaughan, and A Guide to Common Freshwater Invertebrates of North America by J. Reese Voshell, Jr.

While considerable effort has been made to be as accurate as possilbe, I recommend anyone using information found on this site to confirm the data by going to the sources mentioned above, or other qualified resouce materials. Further information on the identification and ecology of aquatic macroinvertebrates can be found from the materials mentioned on the Resources Page. If you have any comments or notice any errors, please contact: . I want this site to be a useful and accurate resource for educators, volunteer water quality monitors, and watershed enthusiasts.

The author would like to acknowledge the following contributors to and supporters of this project:

  • Jeff Adams, Aquatic Programs Director of the Xerces Society, has provided considerable assistance in identifying unfamiliar aquatic macroinvertebrates. In addition to the direct correspondence I have had with him, the Stream Bugs as Biomonitors CD-ROM and Macroinvertebrates of the Pacifc Northwest, A Field Guide he developed have been valuable tools in learning more about aquatic organisms.
  • Judy Bufford is a Watershed Monitoring Program instructor for the Water Resources Education Center, and a Clark County, WA watershed steward. She has participated in a number of water quality monitoring field trips with my 7th grade students and has willingly shared her knowledge of aquatic organisms. In addition, she contributed a number of suggestions toward the the development of my freshwater macroinvertebrate field guide.
  • Dr. Pete Ritson was educational coordinator for the Environmental Information Cooperative at the time that my original field guide was being developed. It was his suggestion that led me to develop a single-page, laminated guide. His encouragement and suggestions toward the project were very helpful.
  • Patrick Edwards, instructor at University of Portland, contributed copies of his guide, Stream Insects of the Pacific Northwest , to my 7th grade science class. He also arranged and taught a grant-funded workshop for teachers on identifying and using aquatic macroinvertebrates for water quality monitoring.
  • Dr. William Feddeler initiated the Watershed Monitoring program for schools in Clark County, WA. It was through his assistance that I first began testing the waters of the East Fork of the Lewis River with my students.
  • Others who have offered encouragement and support along the way include members of the Environmental Information Cooperative (Christine, Hannah, & Carrie), the Water Resources Education Center (Ben & Cory), other teachers in the Watershed Monitoring Network program, staff members and students at CAM Academy and the Battle Ground School District, and members of the Olympic Parks Institute staff.
  • I thank my kids (Jamie, Joel & Jared) for their tolerance and understanding during the development of this site. You're the best!


Modified: October 2015