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The Monarch Butterflies Migrating Now Aren’t The Ones You Saw Last Spring
Posted on Thursday, August 28, 2014 by eNature
Monarch Butterfly
Monarch Butterfly
© Derek Ramsey, CCL
Common Milkweed
Common Milkweed
© Kevin Adams

Fall is just around the cornere throughout most of North America. 

You’ve probably noticed that your local birds are preparing for it— and so are our many of our butterflies.

Monarch butterflies are famous for their annual migrations. Some of these insects travel thousands of miles each fall—an astonishing distance for such fragile creatures.

Yet few people realize that the Monarchs we see in the spring are not necessarily the same ones that fluttered past in the fall.

Beginning in late September, the skies along the Gulf Coast of Texas slowly become filled with meandering groups of Monarchs. Their flight, while not hurried, is purposeful, moving southwest toward a small forest in the highlands of Central Mexico. These butterflies travel from southern Canada and the northern United States at a rate of approximately 50 miles per day. They’ll spend the winter in a few small groves of evergreen trees, with each grove containing as many as 20 million butterflies. Sheltered from the wind and snow, the butterflies conserve energy, for they still have a lot of work ahead of them.

The Monarchs become active again in February. Mating begins, and the air fills with swirling masses of copulating pairs. The first warm days of late March trigger their northward flight. A close look at these butterflies, now eight months old, reveals that their wings are faded and tattered. Still, the Monarchs fan out across the southern United States, looking for Milkweed plants on which to deposit their eggs.

Four days later, the eggs hatch, producing small caterpillars that immediately begin to feed on the Milkweed leaves. Ten to fifteen days later, each caterpillar stops feeding and forms its chrysalis—a beautiful soft green jewel flecked with gold. In another ten to fifteen days the chrysalis splits open, and a new Monarch emerges.

This generation of butterflies mates, lays eggs, and dies within the span of a few weeks. During this time it moves north, following the progress of spring and the emergence of Milkweed.

By the end of summer, two more of these short-lived generations will have repeated the process, ultimately coming to inhabit the Milkweed patches in the far north latitudes.

Thus the Monarchs born in the Northeast and Canada in September are the great great grandchildren of the last Monarchs to inhabit the area. These are the ones that will head to Mexico. They’re significantly larger than the three generations that preceded them and still sexually immature. Rather than mate and lay eggs, they seek out nectar-producing flowers. The nectar serves two purposes: some of it fuels the southward migration, and some of it is converted to fat reserves that sustain the butterflies through the winter.

This incredible annual cycle applies to all Monarchs east of the Rockies. The populations in the West follow a similar pattern, though their migratory path is westward, from the Great Basin to overwintering sites along the Pacific Coast.

Since 1992 MonarchWatch has been carefully tracking Monarch Butterflies as they migrate.  Much of their data comes from the work of volunteers who tag and track the butterflies. They can always use more helpers…..

Are you seeing butterflies in your neighborhood?



Your article is on the migration of Monarchs on the east side of the Rockies.
You might also want to tell the story of the western Monarchs that migrate from Cananda to Central California, wintering in the Santa Cruz and Pacific Grove areas starting in October and returning to Canada in February. As I understand it, this migration takes about five generations to make this round trip.
Here in Santa Cruz we have sizable populations at Natural Bridges State Beach and in Lighthouse Field, part of Ligthouse Field State Beach, as well as scattered locations around town that we try to keep quiet about so as to give the Monarchs their privacy.

Posted by Patrick in Santa Cruz, California on 8/29

Aren’t the butterflies born in the Northeast and Canada in September the great great grandchildren of the ones who left Mexico and not “of the last Monarchs to inhabit the area”? (3rd from last paragraph)

Posted by Sherry on 8/29

so far this year has been way better than last year. Last year I saw a whole lot of nothng,hi year,I saw a few

Posted by emily on 8/29

I raised a monarch from the egg to caterpillar to chysallis to butterfly. I’ve read that they don’t eat each other on purpose only by accident as they feed on leaves, but every time a new tiny caterpillar hatched on a different leaf (but in the same cage)it disappeared, and its milkweed leaf was not eaten at all! Hmmm.
I also have a chrysallis hanging from a tomato right now. We can see the butterfly inside the green covering, with beautiful golden speckles on it that look like real gold in the sunlight. I have no idea how it ended up on a tomato, the nearest milkweed plant is over 6 feet away from my tomato plants!

Posted by Patricia Turk on 8/29

We live near Pacific Grove, CA, where monarchs winter. They line the eucalyptus tree branches by the hundreds…maybe thousands. Because their wings are folded shut, you can’t see them unless you know what you’re looking at. They are amazingly beautiful in flight and we feel gifted to see one now and then in our garden in the summer.

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