Full-grown caterpillars of Pero mizon are to be found in the spring on various shrubs such as Oemleria, Cornus and Salix. They are large and have a pussy-cat face rather similar to that of Biston betularia. How to tell the difference? If it's spring, it's mizon; if it's fall, it's betularia. When fully-fed, the caterpillar pupates, and the adult moth emerges a few weeks later. Eggs are laid in a neat row at the edge of a leaf. Young caterpillars can be found in the fall, and they usually spend the winter in the larval state. There are several colour forms of the caterpillar, apparently chosen to match their surroundings. I show three forms here; the one standing on the reddish dogwood twig is particularly expertly disguised.