Monarch butterfly caterpillar (image) University of California - Berkeley Share Print E-Mail Caption A monarch butterfly caterpillar. Monarchs are intolerant of freezing weather, and typically overwintered in Mexico. They now are overwintering in California, thanks to milder winter temperatures. Credit Noah Whiteman, UC Berkeley Usage Restrictions None Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.