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!

roaches

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.

"samples"

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.

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Unless otherwise stated, all text, images, and video are copyright © 2011 DragonflyWoman.wordpress.com

Aquatic Insect Tolerance Values

fast flowing, cold water

Sampling insects in a clean, high elevation stream

About 6 months ago, I wrote a post about aquatic insects and water quality that highlighted the differences in the diversity of species in a polluted river compared to a clean mountain stream in Arizona.  Considering how much I enjoy this subject, it’s been far too long since I wrote about it!  It’s time to do something about this sorry state of affairs.  My next few Monday posts are thus going to be about how insects are used as indicators of water quality in streams and lakes.

Aquatic insects are very useful for making environmental policy decisions and in deciding when managers need to step in and actively manage a body of water.  I think it’s useful to know how this works!  But first I should introduce the concept of macroinvertebrates.  If you ever delve into the insects-as-indicators-of-water-quality literature, you’ll see this term over and over again.  Although I tend to talk about insects more than the other invertebrates in streams and lakes, not all invertebrates that live in freshwater habitats are insects.   There are lots of other inverts, including crustaceans (crayfish, shrimp, and their relatives), aquatic worms (earthworms, tube worms, leeches, etc), flatworms, mites, snails, and clams.  The inverts are divided into the microinvertebrates and the macroinvertebrates.  Essentially, anything that you can see with the naked eye is a macroinvertebrate.  Everything else is a microinvertebrate.  I personally don’t find this definition very satisfying because one person’s macroinvertebrate might be another person’s microinvertebrate (e.g. my macroinvertebrate is very small).  Any one person’s cutoff for what makes a macroinvertebrate can change over time and as they gain experience too.  Still, water resource managers love the term macroinvertebrate and everyone uses it, including me.

An example of water full of organic pollution. This is a constructed wetland intended to clean up water coming out of a wastewater treatment plant before being released into the river.

In my first post on using aquatic insects as indicators of water quality, I focused on the changes in diversity that you see along the clean to polluted water continuum and I’ll talk about it again in a future post.  The number of species of macroinvertebrates in a stream is a quick and dirty way to compare bodies of water and determine the relative amount of pollution or impairment because clean streams and lakes tends to have more species in them than highly polluted bodies of water.  It isn’t precise though.  A fairly dirty stream can have almost as many macroinvertebrate species in it as a clean stream under the right conditions.  In this situation, it becomes important to consider the specific species that are found in a body of water. This is where tolerance values come in handy.

Tolerance values tell you how tolerant any given species is to pollution in its habitat (go figure).  The scale most commonly used goes from 0 to 10.  Things with low numbers are very sensitive to pollution.  Things with tolerance value numbers closer to 10 tolerate a lot more pollution in their habitats and can live in some pretty nasty water.  And, just to make everything confusing, sometimes you find super tolerant species with scores that go right off the top of the regular scale.  (They’re like Nigel’s amplifier in Spinal Tap – they go to 11!)

Arivaipa Creek looking toward the canyon

A nearly pristine, low elevation stream

Considering how often tolerance values are used in aquatic research and how valuable they are to water resource agencies and managers, I think it is worthwhile to know where tolerance values come from.  It takes a lot of time and effort, and often a lot of money, to calculate tolerance values for macroinvertebrates, but the concept is very simple.  First, someone (often a water manager for a state’s environmental protection department or a scientist) will take measurements of pollution or other impairments in many different bodies of water.  These could be simple physico-chemical measurements (such as pH, dissolved oxygen, temperature), measurements of embeddedness (how far down into the silt/sand the rocks and pebbles are buried) or periphyton (the algae growing on the surfaces of rocks, soil, and plants in the water), or full water chemistry analysis.  Which measurements are taken will depend on the region, the group doing the work, the funding, and the time available to put toward the project.  After measurements are made, bodies of water are grouped according to the level of pollution/impairment they exhibit, such as pristine, impaired, and polluted.

Next, the researchers send out a hoard of samplers to pull out every invert they can find from as many bodies of water as possible.  Some poor group of technicians then “picks” the samples (separates the inverts from the massive amount of junk that you get in aquatic samples such as leaves, sand, silt, twigs, trash, etc) and passes the inverts off to the identification guru to identify.  After all the water measurements and invert ID work is done, then the researchers compare the species present in each water body to its pollution classification and use statistics and other mathematical tools to look for overall trends.

Rio de Flag

A highly impaired, effluent dominated stream downstream of a wastewater treatment plant. Photo by Dave Walker.

Inverts that are found only in pristine lakes and streams and never in impaired or polluted waters have narrow pollution tolerances and are assigned low pollution tolerance values, usually 3 or less.  Inverts found in impaired and pristine waters but not highly polluted waters have a wider tolerance for pollution.  These inverts prefer clean water, but they can tolerate some pollution in their habitats and are usually assigned mid-range values around 5 or 6.  Things commonly found in highly polluted waters get high scores, between 8 and 10, though they are sometimes found in clean water systems too.  And those things with scores of 11?  Well, they can live in some of the filthiest water you can imagine!  I don’t know about you, but I can imagine (and have worked in) some pretty nasty water, and there are insects living in nearly all of them.

It is important to note that macroinvertebrate pollution tolerance values vary from region to region.  Here in Arizona, we can’t use the pollution tolerance values calculated for inverts on the east coast, even when the species are the same, because our waters and the inverts living in them behave differently than those on the coast.  Thus, every region develops their own pollution tolerance values.  When I’ve done water quality studies using insects as indicators of pollution/impairment in the past, I’ve used a list of tolerance values developed within Arizona that was given to me by the Arizona Department of Environmental Quality.  The tolerance values therefore accurately reflect how inverts in Arizona react to pollution/impairment that occur in Arizona.  The list doesn’t have every species, but you can often use what you know about which waters you find them in and published records of their presence to fill in the gaps.

Sabino Canyon

A normally clean, but impaired, stream a few weeks after the end of a major fire. Photo by Dave Walker.

Next Monday I will go through an example of how scientists and water managers use tolerance values by discussing a project I was involved in a few years ago looking at the insects in Arizona’s effluent dominated streams.  Tolerance values played a huge role in the analysis of our results, and it was an interesting (but disgusting) project.  Until then, have a great week – and don’t forget to enter my latest contest!

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Unless otherwise stated, all text, images, and video are copyright © DragonflyWoman.wordpress.com

Friday 5: 5 Fantastic Insect Horror Movies

I am a huge wuss when it comes to watching horror movies.  I am jumpy in general (this might be the result of spending my early childhood in a place that has rattlesnakes in the gazillions, my current city!) so movies where things jump out really bother me.  Movies where things move in creepy ways are incredibly disturbing to me.  That scene from The Exorcist (I saw the director’s cut) where the girl crab-walks down the stairs?  Eeek!  And those horrible torture movies that are popular at the moment (Texas Chainsaw Massacre, the Saw series, etc) worm their way into my brain and stick there so I can’t think of anything else for weeks.  I really hate those movies…  However, I adore cheesy, low-budget, B-movie horror movies.  And guess which group of animals is frequently featured in these gems?  Insects!  Thus I can combine my passion for insects with my craving for bad horror movies on a reasonably regular basis.

Over the years I’ve seen dozens of insect horror movies, but there are a few that I absolutely adore.  Some are brilliant examples of classic horror films, but the others are so cheesy I laugh hysterically all the way through them no matter how many times I see them.  So, without further ado, I present my top 5 insect horror movies:

The Fly

IMDB Rating: 7.0. Image from IMDB.com.

5. The Fly. Now many of you will be familiar with the modern version of The Fly, the one with Jeff Goldblum and Gina Davis that was released in 1986, or maybe The Fly II with Eric Stoltz.  These are both fine insect horror films.  However, if I’m going to watch The Fly, I prefer the 1956 Vincent Price version.  Vincent Price was a brilliant horror actor and really makes this movie work.  You probably all know the story: a scientist develops a teleportation device and tests it on himself.  However, he didn’t know there was a fly in the machine with him when he turned it on.  The result: the scientist’s body comes out the other side with the fly head on top!  Vincent Price’s character is a the brother of the doomed scientist and attempts to help the scientist’s wife cope with her husband’s disfiguration.  The movie is actually good, with skilled actors and a a touching plot.  The end of this movie is fabulous, but I’m not going to ruin it!  You’ll just have to watch it yourself.

Mansquito

IMDB Rating: 3.1. Image from IMDB.com.

4.  Mansquito / Mosquito Man. This is a Sci-Fi Channel exclusive, and if you know anything about made-for-Sci-Fi Channel movies, you know how terrible this movie really is!  The plot is decent enough.  Once again, we have a scientist, this time a woman who is testing some new compound she’s developed on prisoners.  However, an explosion in the lab as the prisoner is about to be injected has disastrous effects!  Both the convict and the scientist begin to transform into giant mosquitoes.  And if that isn’t enough to make you want to run out and watch this tonight, let me just say that the “love” scene between mostly transformed convict and partly transformed scientist is about the most hilariously bad scene ever created for a movie.  This movie definitely falls into the so bad it’s good category, but it made me laugh.  A lot.  Hence its appearance on my list.

Skeeter

IMDB Rating: 2.8. Image from IMDB.com.

3.  Skeeter. This movie follows a standard plot in insect horror movies: pollution caused by man irradiates or otherwise mutates the insects in an area (usually a remote area) and turns them into giants.  Apart from the fact that an insect this big would collapse under its own weight, I really love this particular plot.  I believe Skeeter takes place in a small town in Nevada, a town that has an illegal toxic waste dump conveniently located in a damp cave or mine shaft with a lot of water.  The mosquitoes become gigantic, about the size of a basketball, and go on a killing rampage through the area around the town.  Add to this a love story between a lawman and a woman from the town and you’ve got yourself one fabulous so bad it’s good insect horror movie!

Them

IMDB Rating: 7.4. Image from IMDB.com.

2.  Them! Okay, okay.  I know I should put Them! first for several reasons.  First, this movie is surprisingly detailed and correct when it comes to the science. You can actually learn something about ants watching this movie!  Second, the story is fabulous – atomic testing in New Mexico creates a hoard of ant giants that terrorize the humans who created them.  Third, this is probably THE most classic insect horror movie.  Don’t get me wrong.  Them! is a truly brilliant movie and makes for great commentary on the consequences of the nuclear age.  If I were going to recommend a good insect horror movie to someone, this would be it.  However, I just can’t put this movie above my all-time favorite insect horror movie…

Empire of the Ants

IMDB Rating: 3.2. Image from IMDB.com.

1.  Empire of the Ants.  This movie is pure B-movie greatness!  There’s a ton of bad, overly dramatic acting.  The story is completely ludicrous.  The beginning of the movie is supposed to put the plot into context – we humans are destroying the planet, consequences be damned – but the narration is so over the top it’s impossible to take the movie seriously.  Once again, we have giant ants created due to toxic waste.  Once again, the giant ants are terrorizing people, this time a group of potential investors who are visiting a bogus land-development project headed by the scamming Joan Collins.  They have to fight off the ants to save their lives, only to get into worse and worse situations with fewer and fewer people as they go along.  The movie oozes more cheese than a big pile of nachos!  But I think it’s absolutely hilarious to watch.  Plus, the ants in this movie are actually pretty cool for the most part.  I can’t be sure, but I believe they filmed some scenes through an ant farm-like enclosure (or superimposed film of ants in such an enclosure) so that the ants crawling on the buildings and the docks look much more realistic than they do in most insect horror movies.  Still, the big showdown between the ants and the survivors at the end is so shockingly bad it can make you forget about the more redeeming qualities of this movie.  I was recently very excited (perhaps too excited!) to discover that it had been released on DVD, so you might actually be able to get your hands on a copy of this gem of an insect horror movie.  I highly recommend it.

So that’s my list.  Anyone want to share their favorite insect horror movie?  If so, leave a comment below!  I’d love to discover a new movie or two to watch!

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Unless otherwise stated, all text, images, and video are copyright © 2011 DragonflyWoman.wordpress.com