Fleeting Beauty
The incredible life journey of the Monarch butterflies
Leafing through a tattered Lonely Planet guide to Mexico (courteously provided by my Airbnb host), I notice an attraction that sounds like it would be right up my alley: a tour through a Monarch Butterfly Reserve. The site is not easy to get to: it involves a flight to Mexico City, three buses and a taxi tide, followed by a trek up to 10,000 feet in the Sierra Madre mountains where the butterflies winter from late October through March. But if the Lonely Planet guide is to be trusted, this is a phenomenon I would not want to miss:
“Every autumn, millions of monarch butterflies flock to these forested Mexican highlands for their winter hibernation, having flown all the way from the Great Lakes region of the US and Canada, some 4500 km away. When the sun rises and warms the forest, they take to the sky in gold and orange flurries, descending to the humid forest floor for the hottest part of the day. By mid-afternoon they often carpet the ground brilliantly. The best time to see them is on a warm, sunny afternoon in February - they don't fly as much in cool weather.”
The guide calls it the “butterfly Burning Man”, which makes me want to go there even more. I look up the Butterfly Reserve on Google Maps and read a couple of reviews. Julia gave it three stars back in November because the butterflies had not arrived yet. However, it is now December, and the butterflies would have surely made their way to the winter sanctuary by now—or could 2023 be the year they break the century-long tradition?
Monarch is the only butterfly known to annually migrate between north and south as birds do, with some flying as far as 3000 miles. It takes multiple generations to make the full journey north every spring. The butterflies mate, lay eggs and feast on native milkweed plants along the way. On the way back, however, the entire trip is made by a single butterfly generation over two months. This strange behavior is one of the most complex migration patterns in the animal kingdom, and scientists still have no idea how or why they do it.
Monarchs’ winter vacationing in Mexico is not the only thing that makes them interesting. The Monarch butterflies have an incredibly flexible lifespan, ranging from just a couple of weeks up to 9 months, and can self-regulate their metabolism and reproductive cycle. For this reason, they are being studied to understand longevity and fitness adaptation mechanisms. However, the migratory behavior, which these mechanisms are intrinsically linked to, is threatened by habitat destruction, the use of insecticides, and climate change, so scientists might not have anything to study soon.
An ephemeral species
Monarch butterflies became a topic of debate recently over whether or not they should be on the endangered species list. The U.S. Fish and Wildlife Service gave priority to other species in 2020; but the International Union for Conservation of Nature (IUCN) has given Monarchs an Endangered listing in 2022, which means the species is likely to go extinct without significant intervention. The concern is not just the declining numbers, but the fact that some populations have stopped their annual migration.
Their numbers have declined precipitously since the 1980s when the Lonely Planet Guide to Mexico was first published, which makes me wonder if I will be as disappointed as Julia if I make the arduous journey (although not nearly as long as the butterflies make) to central Mexico to try to get a glimpse of their golden flutter. I hesitate. Perhaps the danger of losing the majestic Monarchs is overstated?
In recent years, Monarch butterflies have been spotted wintering in the Southeast of the United States, where it was previously too cold for them to survive. The warmer weather confuses the insects and they stop prematurely in places like Northern Florida and Texas. However, these locations are still susceptible to cold snaps, which can dramatically reduce the numbers of butterflies that survive the winter.
The Eastern population that winters in Mexico has declined by 85% and the Western, which has chosen the California coast for their winter roost, has seen an over 99% drop, although the numbers have since stabilized. Planting of the native milkweed plants helps: these poisonous flowers are essential for the Monarch’s reproduction cycle because they protect the butterfly larva from predators. The milkweed contains cardenolides, heart-arresting toxins, and the birds have learned not to eat the colorful Monarch caterpillars.
The Monarch caterpillars avoid being eaten by birds but they are threatened by an invisible threat: a parasite called Ophryocystis elektroscirrha. The parasitic infection creates holes in the butterfly wings, making them less likely to complete the journey south. For this reason, seasonal migration acts as an important selection mechanism: the butterflies that do make it to Mexico have lower parasitic loads, whereas the ones that have stopped migrating contribute to spreading the disease.
There is another noticeable effect present in the butterflies that have stopped migrating: a decrease in size. The healthy Monarch adult's wingspan ranges from 3.5 to 4.0 inches. The butterflies are able to travel such great distances thanks to their large wings. If they are to stop migrating, there will be no more selective pressure for large wing span, and the majestic monarchs will get noticeably smaller.
The butterflies’ life journey is guided by light. Not only do they know that it’s time to start moving as soon as the vernal equinox arrives, they know where they need to go thanks to a “time-compensated sun compass”—a navigational system made up of the light receptors in their eyes and the precise circadian clock that lets them determine the direction of their journey based on the position the sun at a given time of year. It’s a GPS system that does not require any electronics—and another thing we can learn from studying the Monarchs before they “forget” how to use it.
A journey of a thousand lifetimes
I never got to see the Monarch Butterfly Reserve in Mexico. But by a stroke of luck, I got to witness the incredible phenomenon of thousands of butterflies clustering together for their winter gathering this week in California. Over the weekend, I visited Natural Bridges Park near Santa Cruz to see an arch in a cliff carved out by the swishing waves of the Pacific. Unbeknownst to me, the nearby eucalyptus grove was one of the few places Monarchs have chosen as their roosting site.
The vision of thousands of shimmering golden butterflies is mesmerizing. I felt so lucky that I stumbled upon this magical sight, especially knowing how fragile the Monarch migration is today. Spellbound by the ephemeral beauty in front of me, I meditated on the nature of time and how fleeting our own existence is.
It takes multiple generations of Monarchs to journey from Mexico to Canada. Not a single butterfly will even know where that instinct leads them; yet, they are faithful to the internal compass that guides them along the imaginary lines of migration routes. And just as the butterflies obey the call of the hero’s journey of their species, we too follow an unspecified trajectory of human development. We may not know where it will lead us, be we keep following that compass in that abstract direction we call progress.
