Monarch Butterfly Migration

There's a show on NOVA about monarch butterfly's called The Incredible Journey of the Butterfly's. It's 52 minutes and you can watch the full episode online.
I knew that they migrated to Mexico, but that turns out to be only part of the story.

There is a cycle of 4 generations to the Monarch Butterfly's:

• 1st generation is the start of the return trip, they fly from Mexico to Texas
• 2nd generation flies from Texas to Michigan
• 3rd generation flies from Michigan to Canada - each of these 3 generations live only about a month
• But the 4th is the amazing one. That generation flies all the way back to Mexico. They also live for 9 months, 9 times as long as the other 3 generations.

The show reminded me of when i saw thousands of monarch butterfly's on the shore of Lake Erie. It turns out that the hardest part of the journey is the start, flying over the Great Lakes to Michigan. The ones i saw had just completed that part of the trip. But they still had a 2,000 miles to go till Mexico.