The caterpillar when young forms meandering linear mines in the leaves of Salal Gaultheria shallon, but the mines when larger are blotches. The caterpillar remains inside the blotch during winter, feeding slowly, pupating in an oval cocoon, still inside the leaf, as spring approaches. It is difficult to determine exactly how long is spent in the pupal state, because all the action takes place inside the leaf, but the moth emerges in the spring.