Although I have found the caterpillars on Snowberry, their preferred foodplants are Rosaceae shrubs such as Rosa nutkana, Holodiscus discolor and Spiraea douglasii. Eggs are laid in the fall and hatch in the following spring. The caterpillars stay together in a tight bunch while small, but separate when full-grown. The full-grown caterpillar should not be handled, for it causes an irritating itch. Before pupation it wanders for several days, and eventually it forms a pupa in the ground, where it spends a second winter. The adult moth flies strongly during the day (an alternative English name is Day Moth) and can easily be mistaken for a butterfly. When the female lays its eggs in the fall, it has completed its two-year life-cycle.