Flight of The Monarch Butterfly

After being pelted by thousands of migrating monarch butterflies during a 60-mile ride this week, I knew there must be an explanation for this fascinating phenomenon.  Why are they all flying north and where are they going?  It was kind of cool when I was also riding north as I almost felt like I was participating in their private ritual, but as I turned south, the dance turned to combat as I felt monarchs hitting my helmet, arms, and sunglasses.  I was hoping a wayward monarch would not fly straight into my mouth.

flying_butterfliesThe monarch butterfly is the only insect known to migrate annually over major continental distances. There are two basic migrating groups in the North America. The Eastern population is based east of the Rockies; some 300 million of these butterflies migrate from as far north as northern Nova Scotia.  In the east, the Monarchs migrate to Mexico, then leave their Mexican roosts during the second week of March, flying east and north. 

They’re looking for milkweed plants on which to lay their eggs.  These Monarchs have already survived a long southward flight in the fall and winter’s cold; they have escaped predatory birds and other hazards along the way, and they are the only Monarchs left that can produce a new generation.  If they return too early, before the milkweed is up in the spring, they will not be able to lay their eggs and continue the cycle. 

The Monarchs we see in Northern California have come from the Rocky Mountains.  After three generations migrate the fourth generation returns to winter over.  The ones who return are the children’s grandchildren of the ones there now.  That explains why I haven’t seen these Monarchs at least the last couple of years.  The ones who spread out all summer only live six weeks or so.  I think I saw lots of these Monarchs…they looked very tired.  The ones who migrate back in the fall live about five months to start the process again.  

Monarch butterflies arrive in California in October and hang in the eucalyptus trees through February. November through late January are ideal times to see these creatures, especially in the Montery area.  November is great as they are still arriving and more active.  In the spring they start spreading out again into California, Nevada, Arizona, Utah and other areas.

Over the summer there are three or four generations of Monarchs, depending on the length of the growing season.  Since each female lays hundreds of eggs, the total number of Monarch butterflies increases throughout the summer.  Before the summer ends, there are once again millions of Monarchs all over the U.S. and southern Canada.

OK, there you have it–Monarch mystery solved.  Now get back on your bike and ride!

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2 Responses

  1. Great post. My kids were chasing them for a long time after school today. They are everywhere! It’s cool and beautiful and a bit freaky at the same time. Like Alfred Hitchcock’s “The Birds”, turned all sweet and lovely.

  2. Beautiful. In Houston, they are staying year-round due to our mild winters. I feed the caterpillars and protect them in a cage until the cocoons hatch out. I would love to start tagging them to document their trips. They are fascinating.

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