Cover photo: Monarchs rest on a high tide bush along Maryland’s Wicomico River on a cool September morning. (Dave Harp)
How are monarch butterflies really doing? Could their presence in backyard gardens be a sign of stronger populations? The answer to these questions has been the subject of contentious debate in recent years. But one thing scientists agree on is that the orange-winged insects remain gateways to engagement with the local environment — and they still need our help.
In July, the International Union for the Conservation of Nature (IUCN) declared the migratory monarch to be an endangered species. The international decision comes after the U.S. Fish and Wildlife Service decided in 2020 not to recommend monarchs for protection under the Endangered Species Act.
The decision, the agency said, was not because monarch populations are in good health but because other species were considered in even worse condition at the time. The U.S. agency could revisit the issue in 2024, but monarch advocates with the Xerces Society for Invertebrate Conservation said the decision “cannot wait.”
Monarchs (Danaus plexippus) are the only species of butterfly that travels thousands of miles each year between its summer and wintering habitats, coming into contact with a variety of habitats and environmental changes. The distinct eastern and western populations in North America have both been in sharp decline in recent decades.
The IUCN said that the less-studied western population, which winters in California, has plummeted up to 99.9 % in recent decades. That’s from about 10 million in the 1980s to fewer than 2,000 in 2021.
The eastern population, which visits the Chesapeake Bay watershed in the summer and fall, dropped by about 84% from 1996 to 2014, according to the IUCN.
Challenges of butterfly counting
A month before the IUCN confirmed this summer that monarchs are in trouble, a study out of the University of Georgia seemed to reach the opposite conclusion. Researchers there used survey data from the North American Butterfly Association to conclude that the summer population of monarchs has remained relatively stable over the last 25 years. The association works with citizen scientists to conduct two-day butterfly counts at popular locations in the summer.
The paper, published in the journal Global Change Biology, hypothesized that population growth during the summer — when monarchs mate, lay eggs and transform from caterpillars to butterflies — compensates for butterfly losses from migration and winter environmental factors.
But Karen Oberhauser, a professor of entomology and director of the arboretum at the University of Wisconsin, said there were “a lot of problems” with that study. It used observational data largely from the decade leading up to 2018, though more recent data was available. And 2018 alone skewed the numbers, having posted some of the highest monarch numbers in 16 years. The researchers also excluded observations from sites that had no monarch sightings in five years, and they failed to include any regional analysis, Oberhauser said.
“If you talk to people who notice monarchs … the numbers are, in general, going down,” said Oberhauser, who founded the Monarch Larva Monitoring Project while at the University of Minnesota in 1996. “Places where people count monarchs in the summer are not the places where habitat has been lost as much. But we’ve lost habitat in places where people were not counting them.”
For that reason, Oberhauser thinks the overwintering monarch counts that occur in Mexico for the eastern population are the best indicator of their overall health. But anecdotal information from the warmer months, she said, has shown the population declining in the Midwest and the Mid-Atlantic, including the Bay watershed states.
“We work with a ton of community scientists, and this is another example of the really cool analyses we can do when people go out and look for insects,” Pelton told the magazine. “However, you have to talk about the limitations,” which she said include counting at places where butterflies are present in greater numbers.
Why is it so hard to definitively say how monarchs are doing? Like other insects, butterflies can be subject to short-term variations in their numbers that may or may not be evidence of long-term changes. Regional numbers can vary widely as well, and insects, whether they crawl or fly, are just inherently harder to count than larger species.
Nor does it help that the monarchs’ annual migration spans several generations. The northward journey from overwintering grounds (primarily in Mexico) is accomplished by three or four generations, each responsible for a leg of the trip before stopping to lay the eggs of the next generation. The final generation in the fall lays no eggs — or, rather, it does so only after it has returned to its winter grounds and hunkered down until spring, when it gets the mysterious biological signal to start the trip all over again.
Monarchs lay their eggs exclusively on milkweed, which caterpillars also eat. They’ve lost much of that habitat over the decades as it’s been replaced by crops in the country’s agricultural epicenters. But that also means that one of the best ways to help monarchs is by planting native milkweed — whether in the backyard, in a town square or on a college campus.
Back to butterfly school
Milkweed was the gateway to a broader butterfly-raising effort for a pair of biology professors at the College of Southern Maryland in La Plata. The college had already earned a Bee Campus USA designation from the Xerces Society for planting pollinator-friendly gardens, and some of those gardens had milkweed.
Biology professor Paul Billeter found monarch caterpillars on them and brought a few home. When the hungry caterpillars became more numerous than he could handle, his daughter, who works for the Humane Society of the U.S., suggested he recruit others to “foster” the caterpillars until they became butterflies.
That led to a small Butterflies for the Bay program in 2021, funded with a grant from the Chesapeake Bay Trust, to engage more of the community in growing milkweed and caring for monarchs. To find people who could raise butterflies from caterpillars at home, the program worked with a local chapter of Jack and Jill of America, Inc., a nonprofit founded by Black mothers to provide resources for children.
At the end of the project, “we sent everyone home with milkweed seeds to start home gardens,” said Tracey Stuller, another professor at the college and a veterinarian who helped with the program. “We’re not interested in creating caterpillar farmers. What we’re interested in is people planting native plants in their yards.”
The group also participated in a large monarch tagging festival in October on Cobb Island, on the Maryland side of the lower Potomac River. Tagging allows the butterflies to be digitally tracked during their migration. This year, the professors invited the rest of the campus staff to raise monarch caterpillars — and they were surprised by the interest.
“The IT guy was super enthusiastic,” Billeter said.
Rather than finding the insects on nearby milkweed, Billeter this year bought monarch caterpillars with his own money from a small seller in Pennsylvania. He acknowledged that some monarch organizations discourage raising purchased caterpillars, because of fears that monarchs bred in captivity could weaken the genetics of wild ones over time.
“But we look at it as using the monarch for a season to get folks inspired to be more careful with their yards long-term, to trade [non-native plants] for natives,” Stuller said.
Oberhauser said there is a spectrum of opinion on whether such monarch farms are a net good for the monarch population. She said studies have found pronounced genetic differences between wild monarchs and those raised year after year by breeders.
“On the other hand,” she said, “collecting a few caterpillars and rearing them inside? I do that.”
There may be some who frown at bringing monarchs inside at all, Oberhauser said, “but there are minimal risks of them changing genetically.”
The bonus? Those who interact with monarchs are far more likely to plant and maintain the milkweed that the caterpillars need to grow and become butterflies.
Oberhauser recommends these websites to learn more about monarchs, their life cycle and how to help:
- Submit your migrating monarch observations to JourneyNorth.org/Monarchs.
- Learn to tag monarchs or find waystations at MonarchWatch.org.
- Monitor larvae on milkweed as a citizen scientist at CitizenScience.gov/monitor-monarchs.
- Find research, webinars and reliable information at MonarchJointVenture.org.
Caterpillars, patience & a time-lapse camera
For my daughter’s birthday in 2021, a friend with milkweed plants brought us a bouquet of the leaves with three hungry monarch caterpillars clinging to them.
With the help of a pop-up cage, the internet and just enough milkweed, my family kept the caterpillars alive for several days until they began to pupate. One by one, our caterpillars crawled up the leafless milkweed stems to the mesh roof of the enclosure, where they threaded a barely visible strand of silk from which to hang. Their black, yellow and white striped bodies grew still as they formed little J shapes hanging from the cage.
Then began the stage of caterpillar observation that requires two things: patience and a time-lapse camera. Thankfully, many modern phones are equipped with the latter. Without it, the incremental changes that turn the squishy caterpillar into a stiff chrysalis would have been imperceptible. I came home from an errand to find a brilliant green shell, with a sparkly diamond half-belt around its upper half, hanging where a caterpillar had been, and then another. (I quickly learned that cocoons are not the right term. Those are what moths form. Butterflies make chrysalises, a word made even more fun when my 4-year-old added an extra -es to his pronunciation.)
Ten days later, we noticed that the chrysalises were turning darker, becoming more translucent. On the 11th day, the first butterfly emerged. We returned home from church that Sunday to find its freshly hatched frame, wings still wrinkled from confinement. Determined to witness at least one of the other two emerging from their chrysalises, I set up my phone to take time-lapse imagery and drained its battery twice in one day. Still, I missed the second emergence. Perhaps the best part of the time-lapse imagery was watching myself walk right by the enclosure multiple times, consumed by some household chore, while the event was unfolding.
But I did catch the last one with my camera: the tiny chrysalis vibrating just before the butterfly’s head appeared, then its front legs pushing open the casing. In a flash, its entire body was out and unraveling, blood visibly pumping into its unfurling wings. I watched the video a half-dozen times and shared it with anyone I thought would care.
We gathered on the porch to release the monarchs on a warm September evening. Their spindly legs touched our hands only briefly, springboards to the great beyond. We wondered if they might make it from our Northern Virginia yard all the way to Central Mexico. Later that week, our monarch-inspired transformation was complete. I bought a monarch book for the kids — and some seeds to grow more milkweed.
— Whitney Pipkin