Monarch butterflies may be thriving after years of decline. Is it a comeback?
On a recent November morning, more than 20,000 western monarch butterflies clustered in a grove of eucalyptus, coating the swaying trees like orange lace. Each year up to 30% of the butterfly’s population meets here in Pismo Beach, California, as the insects migrate thousands of miles west for the winter.
Just a year ago, this vibrant spectacle had all but disappeared. The monarch population has plummeted in recent years, as the vibrant invertebrates struggled to adapt to habitat loss, climate crisis, and harmful pesticide-use across their western range.
Last year less than 200 arrived at this site in 2020 – the lowest number ever recorded – and less than 2,000 were counted across the California coast.
But ahead of the official annual count that takes place around Thanksgiving, early tallies show monarchs may be thriving once again across California. The rise has sparked joy and relief, but the researchers, state park officials, and advocates say that doesn’t mean the species is safe.
Even with the exponential increase, the population is still far short of once-normal numbers. It’s still unclear whether the butterflies are making a dramatic comeback or will continue to decline.
“The takeaway is that the migration isn’t gone, which some people really feared last year,” says Emma Pelton, the senior conservation biologist for the Xerces Society, an organization dedicated to protecting pollinators and other invertebrates. Between 4 million and 10 million butterflies once graced the California coasts before dropping to just over a million at the end of the 1990s. In the decades that followed, the population plateaued at about 200,000.
Then, in 2017, the numbers crashed to fewer than 30,000 butterflies at the annual counts. Monarchs are resilient and adaptive but they continue to face challenges. This year’s uptick is small when put in perspective with past population levels, but “the good news is that it is not too late”, Pelton adds.
A remarkable migration
There’s still a fair amount of mystery surrounding the western monarchs and their incredible annual migration. Each year, they follow a celestial compass and head west from the Rocky Mountains to the coast. Remarkably, each generation of butterflies often returns the same groves along the coast each year, sometimes even a particular tree, without ever having been there before.
Generally, they arrive in California around November and disembark in the spring, heading east as the weather warms. A separate population of monarchs spends the winter in Mexico, coming from Canada and the eastern United States.
Their dedication to routine makes them easier to count each year. But the process isn’t exactly simple, especially when the numbers are low and they are harder to spot. In the Pismo Beach grove, which usually hosts the largest gathering, there are three state parks officials tasked with tallying them before the Thanksgiving count that relies on help from volunteers.
Armed with binoculars, butterfly counters estimate the numbers based on clusters that can be seen in the branches, roughly 50ft (15 meters) from the ground. California state parks has partnered with advocacy organizations to produce a welcoming environment for them. That means planting more of the non-native eucalyptus trees, which the butterflies love to roost in.
The reasons behind this sharp increase remain a mystery. Monarchs that live in the west tend to have three or four generations each year, each with a different role to play in the migration that can span thousands of miles, and there are opportunities at each stage for big shifts.
But what’s driving their precipitous decline is clear. Their historic habitats in grassland ecosystems across the US are being destroyed. Commercial agriculture is eating away at their range which is increasingly laced with deadly pesticides. And, susceptible to both fluctuations and extremes in temperatures, monarchs are vulnerable to climate change. That’s partly why they are considered a so-called “indicator species” revealing the devastating toll taken on other insects and ecosystems.
“The butterflies are just very adaptable and strong,” David James, an entomologist at Washington State University who has spent decades studying the species says. “But they are giving us a warning too – and we need to take heed of that,” he adds. “Their decline is going to affect other organisms.”
‘There’s still time to act’
The butterflies have also felt the impact of extreme heat, fires, and drought, as well as the severe winter storms on the California coast where they spend the winter. “Some of those storms have ripped the trees out and thrown butterflies to the ground,” James says.
But he also believes last year’s extremely low numbers may have been the result of dispersion, not necessarily death.
“When we only had 2,000 overwintering at the traditional sites, at the same time there were many reports inland in San Francisco and the LA area of monarch butterflies reproducing in people’s backyards and parks and gardens throughout the winter,” he says, noting that this spread makes them tricky to count.
But even if last year’s low numbers can be attributed to behavior changes, that’s still a sign climate crisis is causing problems. “They are indicating to us that things are going wrong,” James says.
Individuals can make a difference by planting native nectar plants, including the milkweed that monarchs lay their eggs on and limiting the use of pesticides. Members of the public can also volunteer to monitor monarchs across the west. And, according to Xerces’ Emma Pelton, the promising numbers show that small changes can have a big impact.
“The main message to me is that there’s hope,” she says, noting the way monarchs have inspired the public to reimagine how they see insects and the role that everyone can play in their conservation. “The insect apocalypse narrative and the very real biodiversity crises that we are facing, those can feel really dark” she says. “But the issue is not intractable and we can make a difference. There is still time to act.”