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This Fall’s Monarchs Aren’t The Ones You Saw Last Spring
Posted on Monday, September 27, 2010 by eNature
Monarch Butterfly
Monarch Butterfly
© Derek Ramsey, CCL
Common Milkweed
Common Milkweed
© Kevin Adams

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…..



I live in southern NJ, and have a NWF certified backyard habitat.
I did not see even one Monarch this year 2010 the other kinds of butterflies came as usual.

Posted by John Lauro on 10/2

They are amazing creatures.  I’ve had no luck growing milkweed here in northern California (hot inland area).  Thanks for describing their journey!

Posted by JT on 11/22

I live in Cana VA and I didn’t see a single
monarch until mid September.  I have 1 monarch
catapiller eating leaves now on the milkweed plant.  Will it have time to mature and fly to Mexico?

Posted by carol on 9/21

Yup. They stop off in Santa Cruz CA in November, and give us quite a show!

Posted by liagarden on 9/21

Here are a couple of milkweeds for northern California:
Asclepius spesiosa - (Showy Milkweed), native to California & similar to common milkweed;
Asclepias amplexicaulis (Sand Milkweed) - very drought tolerant;

There are several others that might be appropriate for your area.  Try Prairie Moon Nursery.

Posted by Marilyn on 9/22

Up to 4 monarch butterflies at one time have been fluttering about in my yard over this past week. I live in central New York.

Posted by Debbie on 9/22

A few days makes a big difference in monarch sightings at White Rock Lake in Dallas, Texas.  This year has been very poor for butterfly sightings with extreme drought but yesterday, there were large monarchs nectaring at climbing hempweed vine that grows right beside the water, as well as sweet Autumn clematis that is heavily laden with blooms.  The numbers are still low but it is still very early in the season.

Posted by Brenda on 9/22

I learned the Monarch butterfly’s life is about 9 months, while some of the other butterflies are about one month. A large part of the Monarch’s winter habitat in Mexico was burned a few years ago and many of the Monarchs were distroyed, thus the decline in their population. We used to tag them every fall as they migrated through TX but when their numbers fell off, we stopped because we did not see many. Four of my tags were recovered from deep within Mexico and the University of Kansas sent me the data. I will continue to grow milkweed for the butterflies reproduction and nectar plants for their food.

Posted by Marcie on 9/25

I’m blessed. I live in South Florida and my butterfly garden is always alive with the flights of Monarch and Butterflies.  All year! I use Scarlet Milkweed and Giant Milkweed.  Its rare that a day goes by that I dont see one.  Plant many milkweeds.  They will come. As for Queen Butterflies, those I dont see anywhere nearly as often. Wish I would though.

Posted by Robert on 9/25
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