Benthic Macroinvertebrates


What are benthic macroinvertebrates and why are they so important to the health of our streams? Benthic macroinvertebrates are aquatic animals that lack a backbone and are generally visible to the naked eye. They live at the bottom of streams for at least some portion of their lives. They can be found under logs, sediment, rocks and aquatic vegetation.

Some common examples of these animals are: crayfish, clams, snails, aquatic worms, and a variety of aquatic insect larvae, such as stoneflies, caddisflies, mayflies, dragonflies and damselflies. In addition to being an integral part of the aquatic food chain, they are also used to draw conclusions about the overall health of our streams.

How are macroinvertebrates used to measure stream health? Macroinvertebrates, unlike fish and other aquatic vertebrates, are less mobile and therefore less able to escape the effects of habitat degradation. Their abundance and species diversity can be used to measure stream health. They live year-round in the stream which helps in continual water quality studies. Each species responds to contaminants and stress differently. This allows for better determination of problems that are plaguing our streams. In addition, certain macroinvertebrates such as stoneflies, caddisflies and mayflies can also act as early warning indicators of changes to the stream, in particular, through contamination from point and nonpoint sources. These specific macroinvertebrates are very sensitive to stream impairment and require good water quality, cool temperatures, and a high concentration of dissolved oxygen to survive.

Macroinvertebrates are collected using a net positioned on the stream bed as rocks and sediment are overturned. After each catch, the macroinvertebrates are identified, sorted by species and recorded on a data sheet. At the end of the stream monitoring session, some simple calculations are made and an ecological score is determined. A typical stream monitoring site should be sampled four times a year during each season to get an accurate assessment of the changing quality of the stream.

Stream monitoring is important for the Chesapeake Bay watershed, home to thousands of different species of plants and animals that all depend on clean water. The macroinvertebrates serve as the first indicators in determining human impairment of our streams. 

  Students collecting macroinvertebrates hellgrammite students sorting macroinvertebrates

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