Water-penny beetles
Psephenidae

Water-penny beetles are small nocturnal insects that can be an indicator of water quality.

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Water-penny beetles are round and copper colored with shells that cover their head and legs, making them appear similar to a penny, hence their name. (Photo by Will Parson/Chesapeake Bay Program)

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Appearance

Water-penny beetles are small insects with an oval or circular shell and amber or copper coloring. As juveniles, water-penny beetles' shells cover their head and legs when they are viewed from above, and they appear quite flat from the side, making them look much like a penny.

Feeding

Water-penny beetles mostly feed on algae that collects on rocks and stones in freshwater streams. Some adults do not feed.

Predators

Freshwater trout are main predators of water-penny beetles. However, the beetles do a good job of hiding from predators during the day and becoming active at night. Some frogs and larger water insects have also been known to feed on water-penny beetles. 

Reproduction and life cycle

Female water-penny beetles lay eggs at the edge of a stream or shore where their larvae will live. The beetle stays in its larval stage for the majority of its lifetime, which is about one year. Once they are large enough to pupate and emerge as adults, water-penny beetles locate the opposite sex and lay eggs, and do not live long in this stage.

Did you know?

  • Water-penny beetles are a sign of healthy water quality as they cannot live with high volumes of pollution, sediment or algae growth.
  • The beetles use their legs to scrape algae off of rocks for food.
  • Unlike most beetles which are more oval shaped, the water-penny beetle is round, hence their name. 

Sources and additional information

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