Beetles, Pacific Northwest
Predaceous Diving Beetle are usually black or dark brown, sometimes with green, bronze or brown stripes or spots. The body is oval in shape and very hard, and the hind legs are flattened and fringed for swimming.
They are very common in ponds and quiet streams.
They swim by moving their hind legs simultaneously like a frog which differentiates them from the similar looking water scavenger beetles who move their hind legs alternately.
The adults sometimes leave the water at night to fly to other water bodies.
While flying they are often attracted to lights. The larvae are sometimes called water tigers. Both the larvae and adults are predaceous and feed on other aquatic arthropods and small aquatic animals including fish.