Every fall, hundreds of millions of monarch butterflies begin multi-generational migrations as long as 5,000 miles.
Birds do it, fish do it, mammals do it and even certain insects do it. They migrate. Species of all kinds travel significant—and often unimaginable—distances to find food, a mate or better weather.
The Arctic Tern holds the record for the longest migration of any animal: over 44,000 miles, from the Arctic to Antarctica. Recently, an Eastern Gray Whale set the record for the longest migration of any mammal: over 14,000 miles from Russian waters to Mexican waters and back. Massive herds of wildebeests (sometimes measuring 25 miles long) complete circular migrations up to 1,000 miles on the Serengeti. And every fall, hundreds of millions of monarch butterflies complete round-trip migrations as long as 5,000 miles.
Well, that’s not quite true. Individual monarchs rarely live long enough to complete their lengthy and time-consuming round-trip migrations, so their great-grandchildren finish for them.
Imagine a butterfly in Boston emerging from its chrysalis in late summer or early fall. Monarchs that emerge during this time of year are biologically different from those that emerge earlier in summer. The seasonal changes in light and temperature cause them to delay mating until the following spring. Meanwhile the days are getting shorter, the nights cooler and monarchs cannot survive the long, cold winters of the north. So this late-summer monarch, despite being a primarily solitary creature, starts to huddle together with other late-summer monarchs at night, to stay warm, until it is time to go. And then she heads south with the other members of her “migrant generation” of monarchs.
For the most part, monarchs that live west of the Rocky Mountains migrate to the California coast; monarchs east of the Rockies fly farther south to forested mountains just northwest of Mexico City. As our theoretical butterfly was born in Boston, east of the Rockies, she will head south to Mexico, a trip of over 2,200 miles. She will live off stored fat in her abdomen, and nectar she drinks at her rest stops. Mysteriously, despite the great distance this little creature with only a 4 to-5-inch wingspan will fly, she will gain weight during her long journey. Scientists don’t understand how monarchs gain weight when expending so much energy, but some speculate that they may glide on air currents to conserve fuel.
If factors are in her favor, our butterfly will find her way to Mexico, to the overwintering site of her ancestors. No one knows exactly how monarchs find their way to the same overwintering sites, but scientists are starting to develop theories. Professor Steven Reppert, a neurobiologist at the University of Massachusetts, studies the monarch’s brain. He identified light sensitive molecules that may help the butterflies calculate their direction of flight using the position of the sun. These same molecules are sensitive to magnetic fields, which may explain how the butterflies can find their way even on cloudy days.
Once at her destination in Mexico, our butterfly will enter a hibernation-like state called “diapause” for a few months. In late January and early February, as the days start to lengthen and warm up, she will awaken and mate. By late February and early March, she will begin her long journey back north to Boston.
But her journey will be interrupted. She will need to stop and lay her eggs in milkweed somewhere along the way. Milkweed is described as “host plant” for monarchs because monarchs lay their eggs on the plant, and once the eggs hatch, the caterpillars consume the milkweed as food. Unfortunately, there has been a decline in milkweed due to development, pesticides, herbicides and other factors, and, “If you don’t have the host plant, you don’t have the butterfly,” explains David Marriott, the director and founder of The Monarch Program (monarchprogram.org).
If our butterfly is very lucky, she will find milkweed, and lay her eggs. And then, within a week or two, she will die. But her offspring will hatch and continue her journey home, and her daughters like her, will stop along the way, mate, and if they find milkweed, they will lay eggs that will become her grandchildren. Her granddaughters will hopefully make it back to Boston (it takes three to four generations for monarchs east of the Rockies to complete the round trip). They will mate, search for milkweed and lay eggs which will become the great-grandchildren of the migrating monarch with which we began our story.
These great-grandchildren—if born in late summer—will then migrate to the same spot in Mexico as their great-grandmother, thereby beginning yet another cycle of one the most amazing migrations on earth.
Where to See Migrating Monarchs in Mexico
Sixty million to 1 billion Monarch butterflies journey from North America to the forests of western central Mexico each year. Check out the the Monarch Butterfly Biosphere Reserve, a 350 square mile sanctuary that is now a UNESCO World Heritage Site.
Where to See Migrating Monarchs in California
Starting in October, migrating monarchs appear along the coast of California, from Baja California to San Francisco. Here are a few sites that stand out.
• The Goleta Butterfly Grove and the Coronado Butterfly Preserve, Goleta, CA
• Natural Bridges State Beach, Santa Cruz, CA
• The Monarch Habitat Sanctuary, Pacific Grove, CA
Learn More
What You Can Do: Plant a Waystation
You can help provide the resources that monarchs need by creating "Monarch Waystations" (monarch habitats) in your backyard, community gardens, schools, parks and other available land. An easy way to establish a new Monarch Waystation is to order a Monarch Waystation Seed Kit developed by Monarch Watch (monarchwatch.org).
Monarch Waystation Seed Kits are available for $16 and include 9 varieties of nectar and monarch host plants, as well as a detailed "Creating a Monarch Waystation" guide. Kits may be ordered via the Monarch Watch Shop online at shop.monarchwatch.org or by calling (800) 780-9986.
Each Monarch Waystation Seed Kit includes a total of nine seed packs, including milkweeds and additional nectar plants. The actual species included in each kit may vary due to seed availability and your location. If you want to collect the seeds on your own, use the lists below.
For gardens east of the Rocky Mountains:
MILKWEED
Butterfly Weed (Asclepias tuberosa)
Common Milkweed (Asclepias syriaca)
Swamp Milkweed (Asclepias incarnata)
GENERAL NECTAR PLANTS
Indian Blanket (Gaillardia pulchella)
Purple Coneflower (Echinacea purpurea)
Joe Pye Weed (Eupatorium purpureum)
Scarlet Sage (Salvia coccinea)
Tithonia Torch, Mexican Sunflower (Tithonia)
Zinnia (Zinnia elegans)
Dahlia (Dahlia hortensis)
For gardens west of the Rocky Mountains:
MILKWEED
Butterfly Weed (Asclepias tuberosa)
Narrowleaf Milkweed (Asclepias fascicularis)
Showy Milkweed (Asclepias speciosa)
Swamp Milkweed (Asclepias incarnata)
GENERAL NECTAR PLANTS
Blue Sage (Salvia farinacea)
Chia (Salvia columbariae)
Scarlet Sage (Salvia coccinea)
Tithonia Torch, Mexican Sunflower (Tithonia)
Zinnia (Zinnia elegans)
Dahlia (Dahlia hortensis)
If your monarch habitat meets or exceeds the general description of a Monarch Waystation, your habitat may be certified by Monarch Watch as an official Monarch Waystation!
The "Creating a Monarch Waystation" guide that is included in these kits is also available as a downloadable PDF here.