An adult Water Penny looks like many types of beetle: six legs, black body, shiny, and small. Its larval stage looks quite unlike most beetle larvae. Instead of a worm-like, white grub with a brown head curling in the soil, this larva looks like a legless oval and is aquatic. Its copper color, round shape, and water habitat helped coin its common name. It is often compared to a trilobite, whose fossil is a similar shape with armor plating. Young Water Pennies are often found clinging to underwater stones and rocks in well-circulated streams, rivers, and lakeshores. They may even hold fast to sunken wood. Feathery gills allow them to breathe. Legs are hidden under the ‘shell’ and have scrapers used to nibble algae on the substrate they adhere to. They also eat decaying organic matter in the water. Once in adult form, they live on land, but near the water they came from.
The presence of Water Pennies signifies good water quality. In unhealthy, polluted streams that have overgrown algae or deep sediment, their ability to cling to stones and rocks is compromised, so they cannot establish a population. Looking for Water Pennies in shallow water can be fun for those who don’t mind getting their feet wet.
Scientific Name: Psephenus spp.
Size (Adult; Length): 4mm to 6mm (0.16in to 0.23in)
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Antennae: Beetles have a pair of antennae on the head used as sensors.
Head: The head is home to the insect's eyes, antennae, and mandibles (jaws).
Thorax: Holds the three pairs of legs as well as vital internal organs.
Elytron: One of two wing cases on a Beetle that protects its wings (plural: elytra).
Wings: Appendages used for flying and kept under the elytra until needed.
Abdomen: Houses organs related to circulation, reproduction, and excretion.
Legs: Beetles have three pairs of legs located at the thorax, numbering six legs in all.