Stream Bugs of Montgomery County

Montgomery County is home to hundreds of species of aquatic bugs ( Benthic Macroinvertebrates). These aquatic bugs process nutrients and energy, powering the stream ecosystem! Because they are crucial to the stream, they are excellent indicators of stream health.

Damselfly nymph

Damselfly nymph

What is a Benthic Macroinvertebrate or Stream Bug?

  • A small organism that is visible to the naked eye

  • Does not have a backbone

  • Lives on the bottom of streams for at least part of their lives

  • They include aquatic insects, crayfish, mussels, worms and leeches, snails, sponges, and flatworms.

Why Call them Benthic Macroinvertebrates?

Benthic = bottom dwelling

Macro = visible without a microscope

Invertebrates = lack a backbone 

Why are Stream Bugs Important?

Stream bugs are an important member of aquatic communities.  Many stream bugs eat aquatic plants, algae, and terrestrial plants that fall into the water. Those bugs form the base of the food chain and are called Shredders.

Stream bugs are great indicators of stream health, because they:

  • Live in the water for all or most of their life

  • Stay in areas suitable for their survival

  • Are easy to collect

  • Differ in their tolerance to amount and types of pollution

  • Are relatively easy to identify in a laboratory

  • Often live for more than one year

  • Have limited mobility

Montgomery County categorizes stream bugs into groups based on their ability to withstand pollution. Each genus has a unique tolerance value that helps DEP assess the health of our streams.

Common Stream Bugs (Orders)


Mayfly Nymphs (Ephemeroptera)

Image of a stonefly

Stonefly Nymphs (Plecoptera)

Image of Caddisfly

Caddisfly Larvae (Trichoptera)

Image of Dragonfly Nymph

Dragonfly and Damselfly Nymphs (Odonata)

Image of Dobsonfly

Dobsonfly Larvae (Megaloptera)

Image of Riffle Beetles

Water Pennies and Riffle Beetles (Coleoptera)

Image of Blackfly

Midge and Black Fly Larvae (Diptera)

Non-Insect Groups

Image of Gammarus


Image of Corbicula

Freshwater Mussels and Clams


Image of Leech


Image of Snail


Want to learn more about benthic macroinvertebrates? Check out the DNR Factsheet  (PDF, 1.40MB)

Monitoring Stream Bugs

DEP collects a sample of benthic macroinvertebrates from the stream and returns to the laboratory for further sub-sampling. Individuals from the sub-sample are identified (usually to the genus level) and enumerated. From these data, metrics are calculated, scored, and then summed to obtain a final Benthic IBI score.

Interested in DEP monitoring data? Visit our Monitoring Data webpage for a list of the different data sets the County collects, including our Benthic Macroinvertebrate data.