What Critters Tell Us About Water Quality - A Macro Invertabrate Lesson
Grades: 3 and up
Group Size: Any
Location: Inside Classroom
Length: 30 minutes - 1 hour
Materials Needed
To prepare for this program, you will need to collect insect samples ahead of time. You may choose to collect samples from streams ahead of time and have them preserved in a 70% solution of ethyl alcohol and stream water. Even better, bring in fresh samples unless ice cover prevents it.
You will need the following equipment:
- a screen to strain out the alcohol
- cafeteria-style trays to put the samples into(or Styrofoam meat trays)
- tweezers
- pencils and data sheets to record insect types and numbers
- dichotomous keys (or picture key)
- bell jars and alcohol
- kick net cups (to put similar samples into) or cottage cheese or yogurt containers
- small inexpensive hand lenses
- rock baskets and kick nets (as examples of collection methods, optional)
Background
The purpose of this program is to teach students about water quality from the point of view of aquatic insects. This program is very hands on, and requires students to not only learn to use dichotomous keys to identify aquatic insects, but then they have to determine if samples come from the same or different streams. Students have shown a great deal of interest in this activity. They find it complex enough to be challenging, but not so hard that they lose attention.
Procedure
1. To prepare for this program, run the samples through a fine sieve to wash out the alcohol. Then, put the samples into four trays in four areas of the room. It works well to have 4-6 students per station. Put water into the tray enough to just cover the tray bottom and small rocks. Put a couple of sets of tweezers, a data sheet, pencils, cups, and a hand lens next to each station.
2. When the students come in, put them in a circle in the front of the room. You want to spend some time talking about water. Ask them why we care about clean water? Ask them what pollutes water. What are specific pollutants (kids will give a range of answers). Ask them how to tell if water is clean (kids should tell you to chemically test the water, amongst other answers). You then want to push them to think of other ways to know water is clean. They may say to test the fish or other animals in the stream. Rarely if ever do they make the connection to insects in the stream. At that point I get them to tell me what a benthic macroinvertebrate (BMIs) is. I get them to break the word into parts (invertebrate, macro, and then benthic). I tell them that different BMIs like different kinds of conditions in water. Or talk to them about Water Canaries - how the bugs are an indicator of how clean the water is: the same as canaries showed the miners whether the air in coal mines was safe to breathe. Show them the kick nets and rock baskets and explain their use.
3. The next step is to get the students to consider tolerance levels. One way to bring this up is to ask the students if the room smells funny. Generally some of the students walk into the room saying that the room smells funny from the insects preserved in alcohol. Others don’t seem to mind it. I use that as an example of how some insects are more tolerant to pollution than others. I then show the students pictures of different insects that they will encounter when they start to work with the samples. Hand out the dichotomous keys or picture keys, one to each group. Then discuss the specific features that distinguish one insect from another and specific features that allow an insect to live in a specific place in the stream. For instance, stone flies have two tails and two hooks on their legs to help them hold on to rocks in fast flowing water. Also give students relative ratings of tolerance for the different insects.
4. About now, the students are ready to do something. Break the students into groups and send each group to a station. Tell them to go through the trays and pick out insects. One student keeps track of the number of insects found by putting tally marks on the data sheet. They should put similar looking insects into cups. Other students in the group should use the key to identify the insects. I try to work to ensure that each student identifies at least one insect from the key. Students generally find the large insects first, so you need to circulate around the tables to make sure that each student gets time using the data sheet, picking insects and identifying the insect family. 5. It takes about 15 – 20 minutes to examine the insects at the station. Then, the students need to report back on what they found. Have each group report on the total number of insects and the number of different insects (diversity) they found in their samples. Make this data into a bar graph at the board as they report out. Assist them through discussion in comparing the results from each station to assess whether the insects at each station come from the same or different streams. Ask the students to support their conclusion. Note: If you collect from high quality streams, you will have good diversity and a lot of pollution intolerant species. Sample from fast and slow moving parts of streams and combine these samples. Sometimes, you can have samples from fast and slow moving parts of streams and see if the students can tell the difference.
6. Lastly, tell them where the samples came from, what the land use is in the area, and why the samples may indicate good or poor water quality.
Challenges
A couple of things to consider: Always use ethyl alcohol, not methyl alcohol to preserve your insects. Sharp pointed tweezers can be hazardous. Have students use them carefully.
References
A picture key from the Maine Department of Environmental Protection is included with this activity. Another, more extensive dichotomous key is available through the Stream Study Homepage at the Izaak Walton League.
So, students could do the key over the Internet if that is possible in the facility where the festival is held. If not, the book is also available from the Izaak Walton League.
John M. Jemison, Jr.
Water Quality Specialist
University of Maine Cooperative Extension
495 College Ave.
Orono, ME 04473
207-581-3241
