Insect Investigations: Aquatic Insects as Indicators of Water Quality

aquatic insects

My mini aquatic insect tank for carrying to classrooms

I promised to post some lesson plans during the semester, but I never had a chance to actually do it.  Today I’m making good on that promise.  As it’s also related to my recent water quality series, I’ll use this post to finish up the series at the same time!

A few weeks ago, I had the opportunity to teach at a top middle school in Tucson, a school that consistently ranks in the top 10 or 20 schools in the nation.  The kids at this school are very smart.  I taught 3 lessons, but the kids were in groups of 5th through 7th graders, all mixed together.  Odd!  These kids were also older than any other kids I’ve worked with over the past semester, so my usual “What is an Insect” presentation just wasn’t going to cut it.  Instead, I planned a presentation on aquatic insects.

One part of my presentation involved the kids doing an activity I developed that focused on using aquatic insects as indicators of water quality.  For the blog here, I’m going to describe how I ran the lesson in the classroom during the hour I had allotted.  However, if anyone wants to use this activity, you can find a more official, printable lesson plan on my Educational Materials page (it will be posted later today – having problems getting it uploaded).  Feel free to use and share it at will!


The roaches I share with the kids travel in this

I start all of my insect lessons by figuring out how much the kids already know about the characteristics of insects – number of legs, body segments, antennae, and wings and where their skeleton is located.  With the more advanced kids at this school, I also asked about spiders, crustaceans, and other arthropods as well.  Once we covered the basics, I got a hissing cockroach out and let them hold and interact with it.  The group of kids were mature enough to be able to pass the roach around without totally freaking out and dropping one of my little guys on the floor – one benefit of working with older, gifted kids!  We discussed what the roaches eat (they’re decomposers of plants) and how they eat (chewing mouthparts).  Then I got a giant water bug out.  I don’t let kids hold them so they won’t get bitten, but I showed them all the piercing-sucking mouthpart up close.  We compared the mouthparts of the water bug to those of the roach and I had them guess some of the amazing things that giant water bugs are capable of eating.

At that point, they’d seen an aquatic insect up close and several water bugs and water scorpions in the clear container at the front of the room, so they were aware that there are insects that live in water.  I spent a couple of minutes talking about aquatic insects and where they live before introducing the idea of using insects as indicators of water quality.  I briefly told them how aquatic entomologists use tolerance values of insects to determine the water quality of a stream or lake, explained the tolerance value scale, and let them ask questions.  Then we did the activity.


The insect "samples" from their "streams"

I had the kids get into four groups and set the tone by telling them that each group was a survey team sampling a different stream in southern Arizona.  They’d collected, sorted, and identified the insects in their samples, but they still needed to calculate the biotic index value to determine how polluted the water was in their stream.  I gave each sampling team an envelope containing 10 cards, the “insects” in their samples.  Each card had a picture, the genus, a common name, and the Arizona tolerance value (see below).  Their job was to calculate the biotic index value by taking the average of the tolerance values for all the insects in their sample.  I also asked them to count the number of species found in their sample and discuss what the number they calculated said about the water quality in their stream.  Then I let them loose!

I let the kids do the math and discuss the results with their groups for about 8 minutes and then got everyone back together.  I had one person from each group share the biotic index value for their stream and what they thought that meant.  After every group shared their results, I told them which specific streams their “insects” were from (I based my cards on actual samples, so they were accurate!) and a few facts about that stream that might impact the water quality.  We discussed their results in light of this new information.  For example, everyone decided that it was natural that the most polluted stream would be the one that only had water in it because a waste water treatment plant dumped its effluent into the streambed.  It was also natural that the stream that had the fewest human visitors was the least polluted.  They also discovered that the number of species was generally higher in less polluted streams than in highly polluted streams and that some insects with very high pollution tolerance values still lived in the cleanest water.  Essentially, they came up with all the ideas I had intended to point out, entirely on their own!

insect cards

The "insects" in the "sample"

The kids were enthralled by the insects that have tolerance values of 11 out of 10, so I ended my presentation by pulling out a water scorpion.  They were an example of and 11, and I let everyone get a close look at it.  I told them a few facts about the insects and we finished the lesson by briefly discussing why that particular insect might be more tolerant to pollution than other insects.  They came up with some great ideas!

All in all, I was happy with the presentation!  I think there was a good mix of live insects and fake insects.  I did some talking, but the kids spent most of the time making observations and doing the activity.  Even though the students at this school might not be the best from which to judge the success of my new activity, the kids seemed to get really into it the activity and asked questions that made it clear that they’d understood the greater implications.  I couldn’t have been happier!  Although my presentation was rather informal, I have some ideas for how to expand the activity to make it a full-blown science lesson that fits into the national science standards for 5-8 graders.  If you’re interested in teaching the activity, check out the lesson plan I’ve posted for more information!

This concludes my series on using aquatic insects as indicators of water quality… for now!  I have a few more topics I’d like to cover, but I think I’ll move on to other subjects for a while and revisit this topic again in the future.


Unless otherwise stated, all text, images, and video are copyright © 2011


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