It won’t be long before the skies of Sierra Chincua, Mexico fills with millions of beautiful monarch butterflies that have left their summer breeding grounds in the eastern U.S. and Canada to find a restful place to spend the winter. Their epic, 3,000-mile journey begins in October and ends in the sacred oyamel fir trees in the mountains of Central Mexico, National Geographic reports. Monarchs will also begin this journey in the western U.S. and while some will make the journey to Central Mexico, most will overwinter on the California coast. Here, they will rest in Monterey Cypress, Monterey Pine, and eucalyptus groves.
Millions of Monarch Butterflies Migrate Every Fall
Western monarch butterflies resting in the midwest. Image license CC Attribution 2.0. Photo by Lisa Hupp/USFWS via Flickr
And while the western migration is a smaller one, the numbers are still stunning. In some places, tens of thousands of the colorful butterflies can be found.
But here’s what the impressive migration looks like in Mexico:
Most of us associate monarchs (Danaus plexippus) with the U.S., but monarch species are found in many places worldwide — including Australia, New Zealand and parts of Europe. A sister species, D. erippus, looks quite similar and ranges widely in South America, all the way down to Tierra del Fuego, the continent’s southern tip.
Danaus plexippus erippus is a subspecies of the commonly known monarch and it is widely distributed in South America. The butterfly shown here is a male. Image license CC Attribution 3.0 by Gabriela Ruellan via Wikimedia Commons
Costa Rica, not to be outdone, also has a large population of D. plexippus, but these monarchs are unique because most stay here year-round.
Monarch butterflies are in decline
Monarch butterflies rest at the Coronado Butterfly Sanctuary in Goleta, California. Image license CC 2.0 by Michael R. Perry via Flickr
Even though they show up in huge numbers in some areas, and some populations remain stable, the same cannot be said for many populations of these fascinating insects on both sides of the U.S. The Xerxes Society for Invertebrate Conservation (XSIC) reports that monarch populations have fallen by 90 percent on the west coast. And in some places, the news is even worse. Natural Bridges State Park, near Santa Cruz, California, recorded 120,000 monarchs in 1997. By 2009, that number fell to just 480 butterflies. How sad.
Their habitat is shrinking
The situation is equally dire for the eastern population. In Mexico, scientists conducting a 2012 survey in the Monarch Butterfly Biosphere Reserve in Michoacán, found the insects occupied 59 percent less land than they had the year before, National Geographic reports.
The scientists found nine butterfly colonies occupying just 2.94 acres (1.19 hectares) of land as compared to the same number of colonies occupying 7.14 acres (2.89 hectares) in 2011 and 44.9 acres (18.19 hectares) in 1997.
This isn’t the only reason the butterflies are declining
Milkweed is the only plant monarch caterpillars feed on. Image license CC SA 3.0 by Hectonichus via Wikimedia Commons
Milkweed, which their caterpillars depend on, is vanishing and climate change is also having an impact. With climate change, there’s been freezing temperatures and heavy rain. And the butterflies only lay their eggs on milkweed plants and when the young caterpillars hatch, that’s what they eat as their first meal.
Asclepias curassavica is a type of milkweed that we sometimes grow in our garden. Monarch butterflies love it! Image license CC Attribution 2.0 by Carrotmadman6 via Wikimedia Commons
Farmers, however, have a dim view of the once widespread plant and regularly kill it with herbicides to make room for corn and soybeans. Monarchs frequent corn and soybean fields because after all, that’s where their host plants were formerly found.
Monarch butterflies fare a bit better in Costa Rica
Here, monarchs have faced other challenges that fortunately haven’t been so extreme, noted Ricardo Murillo, a biologist at the University of Costa Rica.
“We will not see the same effects, but we will see different effects,” he said. “With the cementing of the countryside, the destruction of habitats, the emergence of more crops such as pineapple, banana and livestock, the population of the monarch butterfly is going down.”
And while insect populations are rapidly declining all around the world, researcher Lee Dyer and his colleagues have been studying them at La Selva Biological Station in Costa Rica since 1991. The researchers do this by attaching a white sheet under a black light (which many insects love.) Decades ago, insects would have swarmed the light and the sheet. Now there’s none, he said.
This is truly depressing news. Costa Rica has truly astounding butterflies and it’s sad to think such beauty is declining. We have many species of Morpho butterflies, and all of them are beautiful.
Morpho menelaus amathonte is just one of many beautiful species of Morpho butterfly in Costa Rica. Image license CC SA 3.0 by Notafly via Wikimedia Commons
In our garden, we’ve planted lantana, which many butterfly species love, as well as a species of tithonia (we’re not sure which one it is), and cosmos. We will also be planting milkweed, and in our small way, we do whatever we can to help butterflies.
The butterfly Thisbe lycorea in our garden. Image by the author, all rights reserved 
Chlosyne janais visiting our garden. Image by the author. All rights reserved
But there’s a bit of good news — milkweed plants and seeds are available at many retailers and with those colorful flowers, they make a beautiful addition to any garden. And by planting it, you’re making life a little easier for monarchs.
The video below has excellent tips for planting a butterfly garden.
Featured Image license CC 2.0 by Randy via Wikimedia Commons
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