A penny for your water quality

While they are physically small, the role water-penny beetles play in the Chesapeake Bay ecosystem is anything but. Deriving its name from their penny-like appearance, water-penny beetles have a copper colored, circular shell that covers its extremities. This camouflages the insect when it is attached to its rocky habitat, protecting it from predators. After spending most of the day hiding itself from threats, water-penny beetles become active at night in search of algae and decaying organic material that has collected on rocks.

Because algae is the main source of food for water-penny beetles, the beetles play a small part in maintaining water quality by limiting algae growth. Excess algae can block sunlight, which is crucial for underwater grasses, and impede filter feeders from obtaining food. Water-penny beetles are also indicators of water quality in that they are unable to withstand high volumes of pollution. Population loss of water-penny beetles and other aquatic insects can lead to more algae growth, which creates a vicious cycle of poor water quality and an unsuitable habitat for the species. 

Water-penny beetles differ from other insects because they spend most of their lives in their larval stage. Their unique, flattened shape allows them to cling tightly to rocks in fast-moving streams, preventing them from being washed away and enabling them to continue their work grazing on algae. Once they pupate, adult water-penny beetles are focused on mating and laying eggs as they will not live long in this stage.

Their presence also supports the broader food web, serving as prey for fish and amphibians that rely on healthy stream habitats. Water-penny beetles help keep freshwater ecosystems healthy by recycling nutrients, which supports a variety of other creatures in the watershed. Their survival is not only beneficial to water quality but also to the many species that depend on balanced aquatic environments.

Despite often being overlooked as an important critter to the health of the Chesapeake’s waterways, protecting the population of water-penny beetles is crucial for environmental monitoring and efforts in maintaining clean water. As natural defenders of clean water and offering early signs of environmental stress, these tiny “coins” have big value. 

To learn more about water-penny beetles as well as a variety of other insects living in the Bay watershed, visit our field guide.