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Nature Stream Team Does Critters 

Stream Team Does Critters

"Doing critters" is how Stream Teamers describe the capture of small creatures that live on the stream bottom.

After counting them, they return them to the water.

The object is to find out how many individual creatures live on a 36-inch square of streambed at a "riffle." A riffle is a swift, shallow section of a stream where many creatures live. The movement of the water keeps it fresh and aerated. It is where the larvae, the immature form of many water bugs and flies, like to live. The cleaner the water, the more creatures and their larvae will be found. It is a fun and easy way to find out how clean the water is. 
Water-dwelling larvae are numerous. Fish eat both the larvae from the stream bottom and the adults they become. Many critters can only live in very healthy water. Other kinds can survive even in polluted streams. When the Stream Teamers find mostly the kind that can live only in clean water, they know their stream’s water is healthy. When they find only the critters that can live in polluted water, it is time to worry. 
On March 22, 2000, Debra, Susan, Marion and Peter were “doing critters.” They got out the net, found a nice riffle and anchored the bottom of the net with stones and gravel so the moving water would flow into the net. 
Debra and Susan brushed the larger stones with their hands to remove any creatures living on them. While Peter held the net, they stirred the square yard of stream bottom in front of the net with their feet. The water carried all this debris into the net. Then Debra carried the net full of critters to the riverbank.
Debra and Susan washed the critters off the net into a white pan so they could see them better.
Debra carried the pan full of critters and algae (small water plants that live on the stones along with the critters) to the table. 
Everybody sat around the table and sorted the critters they found in the white plastic pan. They used tweezers and ice trays. Different critters went in different sections of the ice trays. That way they kept the critters separate and could count how many there were of each kind. 
Some of the larvae were tiny, especially the youngest ones. To identify them Peter used a magnifier, which held the tiny creature in a few drops of water while being identified. 

In this tray you can see mayfly larvae in the upper right section. Black fly larvae are in the lower section, and a large Dobsonfly larva (hellgramite) is in the first from the left.

Closeup photo of hellgramite, the Dobsonfly larva

The Stream Teamers netted critters from three different places in the riffle to get a good sampling of the critter life in the stream. Here Debra and Marion sort and count them.
Their score on the Stream Team water-rating chart was 27! Since above 23 is Excellent, they were happy. 18-23 is Good. 12-17 is Fair. Less than 12 is poor. 

Here's a list of some of the critters they found and identified: 
Dobson fly
water penny
riffle beetle 

Download PDF Download and print: Stream Insects Identification Key