Butterflies make their first appearance in the spring and fall is when they make their last. And the migration trail of the Monarch butterfly is currently taking them through New York City en route to the mountains of Michoacán, Mexico where they will spend the winter.

The butterflies gracing New York's streets and gardens are mostly coming from Ontario and Quebec.

Hazel Davies, the manager of Living Exhibits at the Museum of Natural History and author of "Do Butterflies Bite?" says millions of Monarchs will hang together in a state like hibernation, but will actually just remain "dormant" for the winter. She says when it begins to get warm again, the butterflies that are migrating south now will lay eggs on milkweeds and will begin to die out. That means while one generation flies south, it is actually the third or fourth generation that returns in the spring.

Davies says Central Park is probably the best place to spot the butterflies, but she's seen them on the Brooklyn Bridge as well.