WSG News Blog

Cool Critters: Aquatic Caterpillar

May 28, 2021

Welcome to our Cool Critters series, where Marine Ecologist Jeff Adams shares the unique features of his favorite marine animals native to the Pacific Northwest. Today’s Cool Critter is the Aquatic Caterpillar!

The Aquatic Caterpillar (Petrophila), also known as the Petrophila Moth, are generally found attached to rocks in warmer rivers and streams. The silken scabs harbor the caterpillars and chrysalises that are adapted for growth, survival under water. These caterpillars also go through metamorphosis entirely underneath the surface of the water! This species is often found east of the Cascades, though can also be found in the Puget Lowlands. 

The picture above shows the scab that is home to the caterpillars before metamorphosis. 

Photo Credit: Jeff Adams, Marine Ecologist, Washington Sea Grant