Springtime means warmer temperatures and the perfect weather for spending some time by your favorite creek or stream. These were always my favorite spots as a kid and I still can’t resist the call of flowing water. If you know what to look for, streams of nearly any size have the potential to reveal a plethora of fascinating critters. These critters make theirs home in the tiny cracks and crevices between rocks or buried in the sandy creek bed. They cling to rock surfaces to avoid getting swept down river while trying to find food or hide out from potential predators under shady rock ledges. We call these tiny aquatic critters macroinvertebrates. What is a macroinvertebrate? Let’s break this word down into smaller parts. First, macro. That means “big enough to see with your eye” (no microscope). And then invertebrate; “without a backbone”. So macroinvertebrates are critters without backbone that are big enough to see. This include larval forms of many insects as well as crustaceans, snails, and more.
* Kids should always be supervised by an adult when playing near water*
Here is a brief introduction to some of my favorite macroinvertebrates and how to find them:
Mayflies and Stoneflies
You will find these by carefully lifting a medium-sized rock in the shallow water near the stream’s edge. Look at the bottom of rock. See those tiny insects with long tails that seem to have flattened themselves to the rock’s surface? These are most likely mayflies and stoneflies. Often, mayflies have three tails while stoneflies have two. There are many species of each of varying sizes and color patterns. Mayflies have gills along their abdomen that look like a wave of tiny fans moving up and down their sides. These gills allow the insects to breath underwater.
Crayfish are crustaceans. They look a lot like tiny lobsters. They have a hard outer shell, called an exoskeleton, covering their body. When the crayfish grows too large for its exoskeleton, it sheds it and grows a new one. You might find crayfish buried under the sand or hiding in dark spots between rocks in still or slow-moving water. They are scavengers who feed on mainly on decaying plant and animal matter. Be careful picking them up; big crayfish can pinch your fingers! The best way to pick them up with with your pointer finger and thumb, grasp their body firmly right behind their claws (then they can’t reach back to pinch you!)
When you turn over a rock in a stream, you may discover what appear to be small tubes or balls of sand grains cemented together and stuck to the rock. These are in fact the homes of caddisflies, another type of insect larvae. Some species create cases using silk and materials they find in their environment. The larva lives inside the casing, poking its head and arms out of one end in order to move around and feed. Eventually, the caddisfly will form a pupa inside its case and emerge as a winged insect. Caddisflies can form cases from many materials, including rock particles and plant material.
These are just a few examples of the amazing diversity of living things found in creeks. What else can you find? Remember to replace all rocks that you turn over and to return all critters to the water. Happy critter catching!