A Monarch on Star Island

This is the time of year when the monarch butterfly begins to make its annual 3000 mile migration from northern United States to the warmer southern regions of California and Mexico.

Their travel south is one of the wonders of nature. Did you know that the monarch butterfly who leaves New England for the south is the great-grandparent of the monarch butterfly that returns?

In all the world, no butterflies migrate like the Monarchs of North America. They are the only butterflies to make such a long, two way migration every year.

Amazingly, they fly in masses to the same winter roosts, often to the exact same trees. Their migration is more the type we expect from birds or whales.

When the late summer and early fall Monarchs emerge from their pupae, or chrysalides, they are biologically and behaviorally different from those emerging in the summer. The shorter days and cooler air of late summer trigger changes. Even though these butterflies look like summer adults, they won't mate or lay eggs until the following spring. Instead, their small bodies prepare for a strenuous flight.

One unsolved mystery is how Monarchs find their overwintering sites each year. Somehow they know their way, even though the butterflies returning to Mexico or California each fall are the great-great-grandchildren of the butterflies that left the previous spring.

No one knows exactly how their homing system works; it is another of the many unanswered questions in the butterfly world.

I took the photo on Star Island in September 2005.