Last spring we were inundated with caterpillars. Sometime in the fall we found a caterpillar and brought it inside. It immediately set it's chrysalis. We waited a few weeks past the time we thought it should have hatched. There were a few times that I looked at that old dried out sack and thought about tossing it. My friend, Tammy, said to hold on to it. That it might hatch in the spring.