Snails cover many of the rocks. This little guy is a pocket snail. Pocket snails only like clean water, so I'm always happy to find them. His operculum is on the right, so I know when I find him everything in the water is right.
While the snails hang out on top of rocks, lots of other critters live underneath. They are invisible to the casual visitor, but I know a secret. I pick up the rocks and I'm always surprised by what I find. First I spot a water penny beetle. They also only like pure water, so I'm happy to find this one crawling on the rocks. He's the round bunp near the bottom center.
I transfer him to my hand and his little feet tickle my finger as he glides gracefully around and around .
Under the next rock, I find mayfly nymphs. They are still pretty small, but they are easy to spot because the minute I lift a rock, they hurry to the bottom side. Note the filmy gills near the back end of this one's abdomen and the three identifying tubes extending from his back end. May flies are also known as fish flies because when they metamorphose, fish love to eat them. Mayfly nymphs are also a sign of healthy water.
My favorite thing to find is caddis fly larvae hiding out in their home-made cases. The larvae spin silk thread and use it to glue small stones or bits of detritus together into cigarette-shaped protective cases. If you look closely, you can see all the small pebbles that make up the shelter. The worm-like larvae is inside.
Not all caddis flies are as talented. Here are a some of the other stone cases I found as I lifted rocks.
My favorite cases are more artistic. This caddisfly must have been dreaming about flying.
I find one last case before calling it a day. It's actually a pair of cases, which is pretty unusual and they are made of rolled up bark.
Next time you go down to the river to cool off, pick up some rocks. There are plenty to choose from. Let me know what you find.