The Monarch butterfly population has been seriously declining in recent years. Every year they make the journey from as far away as Canada and many parts of the US to Mexico where they stay for the winter before heading back north. It’s really pretty amazing. There is movement to help increase the population by planting more host plants for the butterflies to lay eggs on. Then the caterpillars feed on the plants. These photos of Monarch caterpillars was taken in my front yard this morning.
Here’s some info on the migration http://www.monarchwatch.org/tagmig/index.htm