Observing Benthic Macroinvertebrates

Aside from Alaska, Pennsylvania has the most miles of streams of all of the United States! Potter County in particular is special being that it is home to the famous triple divide, meaning three major bodies of water all start here! This is also why Potter County is sometimes called the home of "headwater" streams. 

These tiny headwater streams flow for miles upon miles, eventually to the Gulf of Mexico, Chesapeake Bay, and St. Lawrence River. 

Along with many other organizations, much of the Potter County Conservation District's work aims to improve and conserve these special headwater streams. Our programs and projects ensure this water is kept clean, habitat remains intact for fish and amphibians, and future generations can appreciate one of the many beautiful cornerstone features of God's Country!

Benthic Macroinvertebrates are bugs that live most of their lives in the streams, sometimes lakes, and colder ponds - as eggs and young larvae. They mostly eat leaf litter (detritus), algae, or other macros. Later on, they leave water to enter the air as adults with wings. There are many different kinds of these bugs, or, "macros" and all are food for fish as well as a way to figure our how healthy a stream is. This means they are a "bio-indicator" of stream health.

The combination of bugs you find tells you how healthy the water is, or, the water's quality. Certain bugs can't handle any pollution and will not live in the water if pollution is present. Usually, bugs are categorized in four Pollution Tolerance Groups. Take a look at the ID sheet below to see what bugs belong to each group!

Macros that are Very Intolerant to pollution are in Group 1, Moderately Intolerant is Group 2, Fairly Tolerant is Group 3, and Very Tolerant is Group 4. Finding a stream full of group 3 and 4 macros would mean there is an environmental problem happening nearby that must be investigated. 

You'll need:

A stream, lake, or colder pond

Pans, containers, or other shallow dishes filled with stream water

An ice cube tray filled with stream water

Small spoons or eye droppers to pick the macros up without harming them

Shoes that will protect your toes from stream rocks

Any kind of net that will let water drain through it

Magnifying glasses or small microscopes to zoom in on special parts of the macros that enable them to live (aka, adaptations)

Be sure to record what you find in a notebook or Nature Journal. Written lists as well as drawings are great ways to capture your experience!

1) What bug was my favorite, and why?

2) How many different macros did I find?

3) What pollution tolerance groups did these macros belong to?

4) What do the banks of the stream look like? The stream bottom? Are there many trees here?

5) Is this stream healthy? Why or why not?

1) Use a Biologic Index sheet, which involves a scoring code and simple calculations for macroinvertebrate finds. This gives you a Pollution Tolerance Index Score for each stream you sample!

2) Consider guiding students through saving a specimen in glass test tubes with 70-90% Isopropyl alcohol. Bug collections are a neat tool for educating others and sharing your finds!

3) Have students practice using a simple pH meter, thermometer, or other water chemistry testing supplies to add to macro observation recordings. Some of these testing supplies are available to borrow through the Conservation District!

Vocabulary Used in this Story Map lesson:

• Headwaters - the headwaters of a river or stream are the furthest place from it's confluence (or merging) to another major body of water. Otherwise known as the it's "source."
• Benthic Macroinvertebrate - aka "macro," is a collection of insects and non-insect invertebrates (creatures with no backbone, such as a crayfish) who spend most of their lives in water.
• Detritus - leaf litter, broken down particles of dead insects, fish, or other organisms, or in some cases, sediment matter. Primary food for many macroinvertebrates.
• Bio-indicator - a specie or group of species whose presence and prevalence in an ecosystem helps determine the status or health of the surrounding environment
• Pollution Tolerance Groups - groups in which certain macros are assigned relative to their tolerance to pollution. Most organizations recognize three groups, some will add a fourth. The tolerance to pollution increases with group number (1=little to no tolerance, 4 = very tolerant)
• Adaptations - key characteristics of species that help them survive. In the case of macros, adaptations primarily include their gills, mouth parts, legs, eyes, and body shape.
• Pollution Tolerance Index Score - a quantitative score applied to a particular sampled stream. This gives researchers the ability to objectively compare stream health.
• Data logger - a station adept with hardware that collects chemical data about the water in which it is placed. Common parameters include temperature, depth, velocity (speed), and turbidity (amount of murkiness)

Please use to the links at the end of this lesson for free, printable learning resources!

Photos, video, lesson plan and PCCD Macro ID sheet courtesy of Emily Shosh and the Potter County Conservation District