I just have to share this email I got from my friends Larry Kolczak and Betty Peterson in Ajijic, Mexico. I published photos of one of these caterpillars a few weeks ago.  Here is the end of the story, told by Larry:

Since we live only a few hour’s drive from the mountains in Central Mexico where the Monarch butterflies from Eastern Canada and the U.S. migrate to spend the winter, we figured we’d better give them a helping hand by planting some milkweed in our garden. It is actually a more attractive plant than I imagined. And, it is the only plant on which Monarch butterflies lay their eggs.

After just a week or two, Monarch’s found our plants and began laying their tiny white pearl-like eggs. Here is one right where the sunlit and shadowed parts of the leaf meet.

The eggs hatch about 4 days later. This little guy is busily munching on milkweed.

Milkweed contains some toxic chemicals that don’t affect the Monarch, but will sicken any predator that eats either the caterpillar or the butterfly. As a result, neither has to have camouflaged coloration. Their bright colors serve as a reminder to any predator who ever tried to eat one.