There is a lot more living in a stream, river, or pond then most people realize. Everyone thinks about fish, frogs, crayfish, or lily pads, but there are between 5,000 and 6,500 species of aquatic insects that often go unnoticed. It is estimated that 7% of the 91,000+ North American insects are aquatic or semi-aquatic. In every part and type of waterway, streams, river, lakes and ponds, these organisms can be found. Aquatic insects are a varied group but they all have one thing in common – at one stage during their life cycle, they rely on water.
Macroinvertebrates are organisms without internal skeletons that can be seen with the unaided eye (often considered larger than 0.5mm). Reference to the term “aquatic macroinvertebrates” can include arthropods (insects in all life cycle stages, nymph, larva, pupa, or adult or crustaceans or arachnids), molluscs, and worms. Examples of aquatic macroinvertebrates include mayfly nymphs, stonefly nymphs, dragonfly larvae, midge larvae, crayfish, leeches, aquatic worms, and water beetles. Some of these creatures are called benthic (bottom-dwelling) macroinvertebrates, which means they live in, move along, or attach themselves to the waterway bottom or substrate. Not all aquatic macroinvertebrates remain on the bottom though – some swim through the water column or live on the surface.
Invertebrates are more than just “bugs”. They are an essential part of a viable and sustainable ecosystem. At the bottom of the food chain, aquatic invertebrates provide an important food source for many larger wetland community organisms such as frogs, toads, salamanders and fish.
Aquatic macroinvertebrates can also help humans. Their presence, and numbers, in a body of water are a useful indication of the health of that body of water. Some aquatic invertebrates are sensitive to pollution or poor water quality while others are able to survive in harsher conditions. The presence or absence of certain types of invertebrates is one indication of the quality of water in that place. Therefore if humans want to know about the impacts on water quality they can test it by sampling for invertebrates. Today, as well as doing a variety of chemical tests, conservation authorities also regularly assess watersheds by sampling for macroinvertebrates. This gives a longer range view of water quality because these pollution sensitive species need time to grown and develop over time and could be wiped out quickly by a point source pollutant entering their wetland.