When environmental sampling work involves testing surface water quality ? streams, rivers, lakes, and such ? I usually begin and end with taking samples and measuring the pH. This is what I was trained to do, and this is what will go into the report. However, it?s important to pay attention to aquatic insects during any work involving surface water. Ignore them, and you could be rewarded with a bite from the guy pictured below: a giant water bug (also affectionately known as ?the toe biter?). This insect, along with such legends as the Tarantula Hawk and Bullet Ant, are said to have the most painful bites of any insect ? and yes, giant water bugs live all over the US!


Pictured Above: A giant water bug contemplates making your life very miserable.

Aside from avoiding unimaginable pain, some aquatic insects are very intolerant of pollution, so their presence/absence can be a strong indicator of water health. I?m not advocating buying a net and spending hours catching and identifying insects (who has the time), but there are a couple of key insect species whose presence can tell you a good deal about water quality.

Indicators of good water quality

Stonefly Nymph
Caddisfly Larvae
Mayfly Nymph

Indicators of poor water quality

Black Fly Larvae
Leeches
Midge Fly Larvae

Aquatic insects are good indicators of water quality because:

  • They are affected by chemical and biological conditions of the water.
  • They can show cumulative impacts of pollution.
  • They are easy to identify.

Limitations of using aquatic insects as indicators of water quality

Although insects can be great indicators of overall water quality, they are limited in what they can tell you about why the water quality is the way it is. For example, lack of stoneflies could show that the water has low dissolved oxygen, but it won?t tell us why.

Should you use insects as indicators of water quality?

In my opinion, biological indicators should be part of any water assessment. Although they can?t tell you the specifics that chemical monitoring can, they do paint a broader overall picture of the ecosystem health. They also help us understand the biological effects of the pollutants we are measuring on the stream ecosystem.

If you are interested in a detailed guide on how to identify aquatic insects and what their presence or absence could mean for water quality, please visit: http://www.riverwatch.ab.ca/how_to_monitor/invert_identifying-ident.cfm


Written by: Chris Hollinger

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