The flat, brown, nearly circular aquatic larvae of water penny beetles are more often noticed than the adults. Upon close inspection, you can see the segmented abdomen, thorax, and head. If you inspect the underside of a water penny, you will see 6 legs in the thorax region and tiny, feathery gills under the abdomen. Some species are more circular than others; others have slightly elongated bodies.
Adults are black or brown, oval, flattened beetles, usually wider at the hind end than in the front.
Habitat and Conservation
Biologists can gauge the health of a stream by taking a census of the aquatic insects that live in it. Because water pennies cannot tolerate pollution, high sedimentation, and high amounts of algae and fungi, their presence or absence in a stream is an indicator of the stream’s water quality.