Benthic macroinvertebrates are animals that live at the bottom of streams and lakes, are large enough to be seen with the naked eye (macro) and lack a backbone (invertebrate). In freshwater, they are the immature stages of many insects. You can also find crustaceans (such as kōura/crayfish and shrimps), snails, worms and leeches. Stream bugs are a key part of stream food webs, feeding on periphyton, macrophytes, dead wood or each other. They are also indicators of stream health.
Different methods of sampling macroinvertebrates in streams are:
- kick-net method for stony substrates
- stone method (rubbing stones and debris)
- running the net along the sides of the stream under vegetation for soft, sandy substrates.
These Rivers and Us resources are in a downloadable PDF format. Use them as a guide to the scientific methodology for bug sampling. The bug sampling PDF contains discussion and reflection questions.
Right, so what we’re going to do is to look to see what small creatures are living in the stream, because any big creatures living in the stream are going to rely on the smaller creatures — for food. And it’s one way of knowing whether the stream is very healthy or not is to know what types of creatures are living in there. We call them macroinvertebrates.
Macroinvertebrates are animals that do not have a backbone. They are large enough to be seen with the naked eye. These bugs are a key part of stream food webs, feeding on periphyton, macrophytes, dead wood or each other. They’re also indicators of stream health.
There are different methods of sampling macroinvertebrates in streams. The kick-net method is used in streams that have a stony substrate.
Place your net downstream from the sampling so the current flows through the net and carries the macroinvertebrates into it. Then gently kick at the stones and rocks and logs to dislodge the macroinvertebrates, or you can also use a brush or your hands to dislodge the invertebrates and catch them in the net.
If your stream has a soft, sandy substrate, then run your net along the sides of the stream under the vegetation. This will dislodge any macroinvertebrates and give you a good sample of what bugs are living in your stream.
Once you have your sample in the net, carefully tip it into a bucket or into a white tray full of water from the stream. Be careful to rinse all material off the net as these bugs are small and can cling to the net. Remember to be gentle. These bugs are living, and we want to make sure they can be released back into the stream after we’ve identified them.
When your sample is in the tray, wait for the bugs to start moving around. You’ll need to be patient and observe closely to find them.
When we’ve caught our bugs in the net and we’ve put them into the white tray, we’re going to look carefully at them to see what type of bugs we’ve got.
And this tray helps us sort whether we’ve got number 1, 2, 3 or 4 bugs.
Sort them into similar types of bugs by using a small pipette to transfer them from the big tray to smaller ice cube trays.
Using identification charts, decide what species of macroinvertebrate you have observed and how many are in your sample and record your data.
What does it mean if we have like equal 4 bugs and an equal 1 bug?
That’s a really good question, Jake. What we’re here to do is to find out what type of bugs are living here, and with the numbers of them do give us that clue. Number 4 bugs, though, only love the freshwater – the fresh, clean water – and so we won’t find them in yuck water.
When you come to repeat your sampling, remember it’s important to always use the same testing protocol to ensure your data is robust and can be used to compare over time.
The Fairfield Project
Jordan, Lucy, Hannah, Jess and Sam, Waikato Diocesan School for Girls
Jake and Sarah, Bankwood Primary School
Invertebrate guide, Greater Wellington Regional Council
This video has been developed in partnership with the Waikato Regional Council as part of the Rivers and Us resource.