The MPCA looks for fish, invertebrate (bugs), and plant communities as indicators of water quality. This is called biological monitoring. Some species are less tolerant of pollution than others. Healthy populations of the indicator species often mean that the water body itself is healthy.
Thrives in clean water
Most mayfly larvae feed on algae and bacteria growing on rocks. They live in streams, on the surface of rocks, logs, and vegetation.
Clubtail dragonfly larvae
Clubtail dragonfly larvae burrow into sand, where they breathe by extending the tip of their abdomen above the sand. They can be found in flowing water or lake shores.
A dark colored insect, the hellgrammite (Corydalus cornutus), has an elongate and somewhat flattened body. As an adult, a hellgrammite becomes a dobsonfly. They leave their hiding places at night to hunt for prey. They are large, reaching two to three inches in length when fully grown, and can inflict a painful bite. They live under rocks in turbulent areas of streams.
- The Snail Case Make larvae builds a protective case out of sand and silk that mimics the shape of a snail shell and can be found in the sandy areas of streams and lake shores.
- The Northern Case Maker Caddisfly is found in many habitats and use sand, sticks, and plant pieces to build their case.
Stoneflies need a high amount of dissolved oxygen (DO) to live comfortably. When the DO falls or the temperatures rise, stoneflies disappear. The same goes for most species of trout.
- The Golden stonefly larvae have striking patterns and finely branched gills. They live under logs and stones in rivers and streams.
- The Giant stonefly, when disturbed, giant stonefly larvae can make themselves bleed. The blood tastes bad and confuses predators. They are found in swiftly flowing streams, within leaf packs and snags.
Most abundant in polluted water
Midges are so abundant and diverse that they often make up 50 percent of the species in a water body. They can be found in all aquatic habitats. For more information, visit the U of M Chironomidae Research Group.
The biggest bug in Minnesota – a full 2” long and about 1” wide. Water boatmen breathe using an air bubble held under their wings. They live in standing water in lakes, marshes, and streams.
Giant water bug
These bugs are sometimes called “toe biters" because they can inflict a painful bite with their beak. They are found in lakes, ponds, and marshes with vegetation.
Backswimmers swim belly-up, their bellies are dark and their backs light. Coloring helps bugs hide from predators. They are found in marshes and backwaters of streams.
Predatory leeches feed on the fluid of their prey by crushing the prey in their mouth, and expelling the solid parts of its body. They are found in standing water like marshes and ponds.
When waiting for prey, water scorpions breathe through a long breathing tube that functions like a snorkel. They live in calm water along the edges of ponds and slow streams.
Tolerates polluted water
Dragonflies belong to the insect order Odonata, which includes a closely related group of flying insects called Damselflies. They have existed in their current form for about 200 million years – much older than dinosaurs. For more information, visit the Minnesota Dragonfly Society.
Darner dragonfly larvae
- Darner dragonfly larvae actively stalk their prey, rather than waiting for prey to approach them. They live in the vegetation along lakeshores or streams.
- Skimmer dragonfly larvae can tolerate waters with extensive phosphorus pollution and low dissolved oxygen. They live along edges of ponds and wetlands.
Predaceous diving beetle (adult & larvae)
Predaceous diving beetles can survive in poorly oxygenated water because they breathe from the air. They have a little air bubble stuck to their belly that they breathe from, coming up to the top of the water every few minutes to get more air into their bubble and then they dive back down into the water. They start out as a larva, and then molt into an adult like butterflies do. They live in slow-flowing waters with heavy vegetation.
Adult broad-winged damselflies have striking iridescent blue-green bodies and black wings. The larvae lives along edges of slow-flowing, shaded streams. For more information, visit Wisconsin Odonata survey.
Scuds/side-swimmers are crustaceans, related to lobsters. They proliferate in waters with very few fish. They can be found in shallow areas of streams, springs, ponds, and marshes.