Western Monarch Butterflies (Danaus plexippus) enjoying the California sun on a warmer than usual February day. Usually within the next few days or weeks they will start to migrate away from their wintering areas. Monarch butterflies cannot fly if their body temperature is less than 86 degrees. We generally assume that monarchs can fly if it is above 60 degrees F, and above 50 degrees if it is sunny. The sun allows them to warm their flight muscles enough to fly.