Dec 5, 2018
Monarchs in Mexico—millions of them!
The great butterfly migration has to be seen to be believed
A decade ago I was in Mexico a lot — in Mexico City and in the central Mexican town of Morelia. I was invited by the organisers of world class chess tournaments, and spent weeks at a time in the country. There will be stories about this interesting period of my life. Today it is all about butterflies.
Morelia is located in the state of Michoacán and is one of the most pleasant places you can imagine. The town, the people, the food — and the luscious vegetation, which we northern Europeans can only envy.
You know the little bougainvillea pots we get in our garden centers — the ones we nurture in summer, until they grow to a meter in height? Well, take a look at what a bougainvillea looks like in Morelia. And believe me, all other familiar plant species, which we call “exotic”, are equally over-whelming. Remind me again: why do we live in the frigid north of our globe?
You can click or tap most of the images on this page to enlarge.
Introducing Pilar, one of the organizers, and our guide and chaperone in Morelia. She is from mainland Spain, but knows her way around like nobody else. Pilar is efficient, cheerful, humorous and affectionate, so no wonder that we all sought her company.
One day, strolling through the city, I saw this beautiful creature sitting on a leaf. I identified it — correct me if I am wrong — as an eastern black swallowtail, Papilio polyxenes asterius.
Of course I could not resist catching and photographing it (Pilar: “Let it go, please! Don’t hurt it!”). I obeyed, of course, making sure no harm was done. When I released this butterfly, it sat on my hand for a while, and then calmly flapped over to a blossom near by and started drinking nectar. I caught and released it again, which seemed to leave it completely unfazed. This swallowtail was tame!
Pilar wanted to know how come I could handle butterflies so dexterously, and why I was so interested in them. I told her the tragic story from my childhood, how I had collected and classified Monarch butterflies, and how a German lepidopterist had stolen my collection. She wiped away a tear and fell into thought.
The next day Pilar to me and said: “Fred, I have arranged a trip for us on the free day.” She wouldn’t tell me where we were going, or why, but I trusted her. On the designated day I got into the mini-bus she had arranged, together with a few other visitors from the event.
Our three-hour journey took us to a little hillside community, Macheros, with a population of around 300, where we could take some sustenance.
From Macheros we ascended the hill in a forest path, and I finally realized what Pilar had planned. There were butterflies in the air, more and more as we ascended the trail to the Reserva de Biosfera de la Mariposa Monarca (Mariposa is the charming word for butterfly in Spanish).
When we got to the Monarch Butterfly Biosphere Reserve, which incidentally is a World Heritage site, the air was already full of butterflies. Monarchs.
But we hadn’t seen ‘nutin yet. Entering the forest this is what greeted us. The trees in the picture are naturally green, the orange ar butterflies, covering the stems and the branches. There must have been a million monarchs swarming round the forested mountain — in fact the UNESCO World Heritage site says it “could be perhaps a billion. They bend the branches by their weight, fill the sky when they take flight, and make a sound like light rain with the beating of their wings.”
I am apt to agree with this description — as proof I will show you a few of the scores of pictures I took in the Monarch Butterfly Reserve.
The great North American Monarch migration
“The monarch migration is truly one of the world’s greatest natural wonders,” Monarch Watch tells us. “Each fall, hundreds of millions of monarch butterflies migrate from the United States and Canada to overwintering areas in Mexico and California where they wait out the winter until conditions favor a return flight in the spring.”
What these butterflies do defies imagination and explanation. The North American individuals that emerge from their pupae in August and September don’t mate and lay eggs, but feed vigorously in preparation for the journey to the south. Then they set out, millions of them, mostly in groups, and are able to locate Michoacán, and more specifically the tiny spot in the forest near Macheros. There they congregate on the same pine and oak trees as the generations before them have done.
After mating the monarchs begin the northern migration in March. They only make it part of the way. The females lay their eggs on milkweed bushes they encounter, mainly in Texas and Oklahoma, and the new generation continues on the next leg of the migration. The normal lifespan of these monarchs is less than two months, and in the fall the third generation arrives in the northern breeding locations. There the next generation can embark on the very long journey south, all the way to that little spot in Mexico.
How the migrating Monarchs find Macheros, thousands of miles away, is a mystery. We must remember that the individuals arriving there are the great-great-grandchildren of the butterflies that left Mexico the previous spring. Nobody knows for sure how their homing system works — the brains of these creatures are too small to store the navigational information needed.
So how do they manage to do it? I spoke to an expert, and he gave me a plausible explanation. The monarchs know the general direction and, with the information stored in their genes, can navigate to within a few hundred miles of Macheros. Then their sense of smell takes over. Monarchs can detect just a few molecules of male pheromones, which they follow to the location in the forest. There the remains of males from the previous year fill the air with their pheromones, leading the new generation to their place of congregation. That explains why it is strictly forbidden to collect the wings and bodies of dead butterflies, that litter the ground, and take them out of the park. That could cause monarchs to follow a false scent trail.
Tagging Monarchs
Some years after all this happened I met two young high-school girls from Up-state New York. For some reason I told them about my inspiring trip to Macheros. They were surprised and excited to hear about it. The reason: “Frederic, we have been tagging the monarchs you saw in Mexico!” Turns out these girls had taken part in the “Monarch Watch Tagging Program” and had caught and tagged hundreds of butterflies. Each fall, Monarch Watch distributes more than a quarter of a million tags to thousands of volunteers across North America who attach them monarchs that migrate through their area. The “citizen scientists” record the tag code, tag date, gender of the butterfly, and geographic location, then tag and release them. At the end of the tagging season, these data are submitted to Monarch Watch and added to the database to be used in research.
The majority of recovered tags come from Mexico. Rangers and visitors are encouraged to keep their eyes open for tags, which they find among dead butterflies on the trails or under the monarch-covered trees. Monarch Watch pays $5 for each tag, reasonable compensation for the time and energy spent locating them. If you want to join in the very worthwhile tagging action full information is available on this Monarch Watch page.
Addendum: Today (June 25, 2019) I read that the monarch-butterfly population I described above have declined badly —by 90% in the last 20 years, according to a study from the National Wildlife Federation. Efforts are under way to boost the population, but purchasing large numbers of pupae from commercial suppliers for release has not been successful. For some reason these butterflies do not reliably migrate to Mexico in the winter. The US Fish and Wildlife Service may have to put monarchs on the endangered species list.
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