I found the caterpillar of this moth in early April on Elder. It fed on Elder leaves without much enthusiasm, and I suspect that it might have wandered on to the Elder from some other nearby tree or shrub. Since the caterpillar was full-grown in early April, I would speculate (only!) that winter was spent in the larval state. It spent only a few weeks as a pupa, and the adult moth emerged on the last day of May.