top of page
  • Instagram

One Billion Butterflies: A Claremont Migration Story

A painted lady opens its wings to reveal its characteristic pattern. They are a particularly tough species, able to flourish even when other insect populations are in decline.

If you walked through campus last week, you might have noticed hundreds of orange butterflies that dart and bop and skitter past the Hub, kiss their shadows on the sidewalk, and swoop around the Cube before climbing the air over Kravis. The perfect backdrop for existential musings-- where are they from and where are they going? More fundamentally, what are they?

“Painted ladies,” says Pomona Biology Professor Johnathan C. Wright. The British accent is so natural that the words can never be said in another way. Professor Wright contributed to butterfly census work in the UK, and has done butterfly projects in Bernard Field Station since coming to Claremont 20 years ago. He said that Vanessa cardui are perhaps the most widespread butterfly in the world, and he saw them even when he was growing up in England.

These guys are migrating north from deserts in Mexico and Southern California as they do every year, but having this many is rare. In fact, Professor Wright said there has been a terrible decline of butterflies globally.

“The decline is due to increased pesticide use, grubbing out of native grasslands and old pastures with lots of wildflowers, and also drought and peculiar weather probably linked to climate change,” he said. But painted ladies have several advantages over local California butterflies.

“Because they are incredibly mobile and breed throughout the year, they are much more adaptable in the short-term because they can move away from adverse conditions,” Professor Wright said. “In contrast, butterflies that are monophagous (exploit only one food plant), are very sedentary, and are single brooded (one brood per year) are often the most vulnerable. With the more erratic weather patterns, painted ladies might be a species that actually fares well.”

The high rains in Southern California this year have led to a population boom, since the plants the larvae depend on have flourished early this year. They are breeding as they follow the blooms north, and can sometimes reach all the way to Alaska.

There hasn’t been a painted lady migration on this scale since 2005. Keck Science Professor of Biology Diane Thomson remembers driving back from Anza Borrego then. “This big wave of butterflies came over the ridge and along the road,” she said. “They were so dense that it was almost hard to see out the windshield. It was completely amazing.”

How many butterflies have been flying through Claremont this year? It’s difficult to tell exactly, but Professor Wright and I did the math. Professor Wright counted one butterfly a second flying over his head when viewing a 10-meter range. He first saw the butterflies ten days before we spoke.

On the West Coast, painted ladies follow a narrow migration route up to Canada. On really good years, they might make it all the way up to Alaska.

On the West Coast, painted ladies follow a narrow migration route up to Canada. On really good years, they might make it all the way up to Alaska

“If it’s a hundred-mile band of them going north, 100 times that would be 10 kilometers, 1000 times that would be 100 kilometers-” he’s doing these calculations too fast for me to keep up, but there are around 160 kilometers in a 100 miles — that’s where this estimate comes from.

“So it could be over a thousand times the volume at any one time that I am counting, then extrapolated for however many seconds there are in a day-” he reaches for his phone. “Eight-six-four-hundred seconds in a day,” I offer (Turn it all around or throw it all away). “Oh, very good! So 10 days is 864,000, so close to 1 million seconds in 10 days,” he said. “So a million times … It’s probably on the order of a billion butterflies.”

That’s 1,000,000,000 butterflies.

Birds that eat these butterflies are probably very satiated. So is Ravi Sadhu ‘19, who wrote his senior thesis on bird species that mate in the spring. He said that the butterfly migration was a beautiful thing to watch.

“Apart from the many things that make Claremont so special, watching different animal species such as birds and insects find a home for themselves and add members to their families during the spring is wonderful,” he said. “It reflects how intriguing biodiversity can be, and how the lack of it in urban life is disappointing. I hope this butterfly migration period will inspire all to learn more about species native to Southern California and gain a newfound appreciation for their existence!”

Kandace Fung ‘19 wasn’t as excited about the butterflies as Sadhu. “I thought they were moths,” she said. “My classmate was biking and was hit in the face.” But something changed once she found out they were butterflies, and she agreed that it was beautiful. Once the flowers start withering in the summer, the butterflies migrate back down to their breeding homes in the southwestern deserts. Since the reverse migration route is more dispersed, we don’t see them in the same numbers. But in England, the reverse migration of painted ladies has been a paradox for centuries, Professor Wright said. “Even when you get really good years and they migrate all the way to Scotland, no one has ever convincingly shown that the migrants ever return to Africa,” he said. “There is some speculation that they’re flying higher and we simply lose them, but despite all the efforts there’s not really a convincing case to be made.” For Professor Wright, this trip seems futile. “You can argue that there is a point to migrating north so you can exploit food plants,” he said. “But if you can’t do anything, if all you’re going to do is die up there and not successfully reproduce, why would they evolve that way, why are they doing that?” Maybe the journey doesn’t make evolutionary sense, but there is something to be said about a one-way ticket. Spring Break means graduation is looming ever closer, and I’m struck with an apprehension of all to come. The magnificent painted ladies migration is a reminder and an assurance: we’re all just passing through Claremont.


bottom of page