By Madeline Seveland
Spoiler Alert: Don’t read this article if you occasionally swallow lake water while swimming and don’t want to know what extra “nutrients” you are getting, or don’t like knowing what’s under your feet as you wade through the shallows of a stream or lake.
What’s living in our water? Probably more than you think. The aquatic ecosystems of lakes, rivers and wetlands are fantastically complex and full of life of all sizes. We see the big animals; the fish, amphibians, crayfish, and frogs that call these waters home, but what about the smaller animals we miss.
This month, I’m introducing a few of my favorites. Many insects spend the earlier part of their lives underwater as larvae or pupae. Dragonflies are one such insect.
Their larvae are abundant in standing waters and occur in flowing waters too. They are “sit and wait” predators and feed on many other aquatic bugs.
Their gills are located inside the tip of their abdomens which they can use to jet-propel themselves forward. As adults, these critters can eat over 100 mosquitoes a day!
The giant water bug is a huge, sometimes 2-3 inches, and voracious predator. It can eat animals up to three times its size including tadpoles, fish, frogs, and other insects.
It has strong grasping front legs that it uses to grab its prey and a piercing beak to inject poison. It’s mostly found at the bottom of ponds, but does not have gills so it must make trips to the surface to get air. If found, leave undisturbed, as it can inflict a painful bite on humans too.
In waters all over are small creatures called daphnia (water fleas). These tiny transparent creatures are part of the freshwater plankton (live in the water column and are free floating). Daphnia eat algae, microscopic animals and organic debris. There are many types of Daphnia including a few invasive species such as spiny water fleas that have become a nuisance to fish and fisherman.
A scud or amphipod is one of my favorites. These critters are called “side-swimmers,” zooming through water on their side. This swimming method helps them cut through river currents without being washed downstream and allows fast “get aways” from predators. Scuds have excellent senses of touch which helps them find food at night when they actively search out dinners of decaying plants and animals.
If you are a trout fisherman, I’m sure you are familiar with mayfly larvae.
Mayfly larvae are the most common insects found in cold-water streams. They are considered the “cow” of the stream since they often graze on the algae found on rocks. They have a row of feathery gills along their abdomens and many swim doing a movement similar to our butterfly stroke. As you probably guessed they are excellent food for trout and other fish.
These are just a few of the many small aquatic insects living in our waters. They each play a distinct role in their eco-system and are quite fascinating to watch and learn about. Next time you’re near a creek, wade in and turn over a few rocks, you might just find one critter … or hundreds.
To learn more, check out Wonderful, Wacky, Water Critters on our Education Page at www.co.carver.mn.us/water.