Millions of monarchs make the journey from Canada to Mexico each year, and scientists have determined the butterflies rely on solar cues and the earth’s magnetic field to navigate. But no one knows how they find the precise mountaintop in Mexico upon which they gather, monarch butterfly expert and ecologist Dara Satterfield said.

‘They’ve never been there before,” Satterfield said. “It would have been their great-great-grandparents the previous year.”

Satterfield joined NPR Southwest correspondent John Burnett and Universidad Nacional Autónoma de México (UNAM) ecologist Rodrigo Medellín on a panel discussing borders and pollinators Friday evening at the Pearl Stable. The panel was one of the many events at the annual Monarch Butterfly and Pollinator Festival, organized by Rivard Report co-founder Monika Maeckle. Environmental reporter Brendan Gibbons moderated Friday’s discussion.

Monarch butterflies are not the only insects to migrate long distances, Satterfield said. A study conducted by the Smithsonian Migratory Bird Center found more than 300 insect species migrating around the world, but she said she suspects there are thousands more that researchers don’t know about.

But monarch butterflies are in danger, Satterfield said. In the last 20 years, the population has declined by about 80 percent, and much of that could be attributed to habitat loss. Pollinators have lost about 1 billion acres of wild habitat, which hurts their chances of survival, she said. 

Bats, another major pollinator, also migrate yearly from Mexico to the United States, and Medellín has built a career out of researching bat lives. Nicknamed “the Bat Man of Mexico,” Medellín explained that bats are suffering from some of the same problems caused by climate change as monarch butterflies. Warmer springs may cause the butterflies to migrate faster than usual and travel quicker than the milkweed – their primary source of food – sprouts. In a similar fashion, climate change has led to asynchronicity between the lesser long-nosed bats’ arrival in the U.S. and their supply of food in the Sonoran desert.  

“We’ve been having long rains in the south in Mexico, where they spend the winter, and females stay longer,” Medellín said. “At the same time, the Sonoran desert has also had lots of rain, so the saguaro cactuses advance their flowering season. So when the bats come in, they’re two weeks late, and the flowers are two weeks early. We’ve seen this two or three times.”

(left) Rodrigo Medellín, Universidad Nacional Autónoma de México ecologist

Burnett reported from the Organ Pipe Cactus National Monument earlier in October and witnessed bulldozers pushing over saguaro cacti in Arizona to make room for the border wall.

“It’s a very delicate ecosystem, and there’s a spring there, which has been used for 60,000 years by Native Americans and then Spanish explorers and farmers and traders,” he said. 

“Biologists and conservationists are horrified by what’s about to happen.”

U.S. Customs and Border Patrol will argue that the area of Arizona where the government is constructing a barrier is a “problem area” for human and drug smuggling, Burnett said. But the wall will also block people from going back and forth between the United States and Mexico for short visits, and push them into staying in the U.S. 

“You don’t have a circle of migration, you have one-way migration,” Burnett said.

(right) NPR correspondent John Burnett Rodrigo

If butterflies also lose the ability to migrate, that could prove to be devastating to the population, Satterfield said. Monarch butterflies that shift to a sedentary lifestyle thanks to a tropical strain of milkweed that grows year round are more susceptible to a parasite and can pass that parasite to migrating butterflies, she explained.

“We know from previous work out of the University of Georgia that the migration helps the monarchs stay healthy, and the way to do that is by weeding out the sick,” she said.

That research was made possible by citizen scientists, who told researchers they were still seeing monarch butterflies and caterpillars in their backyards in December, when the butterflies should have made their way to Mexico already, Satterfield said. She encouraged people to find out how to help with monarch research by visiting Project Monarch Health and learn how to sample butterflies. She also said a major way to support pollinators would be to plant native plants and trees.

“The best thing we can do is re-wild the landscape,” she said.

Medellín urged audience members to talk about bats and other pollinators with everyone in their lives. 

“This is all tied in,” he said. “We are one world, we are connected … I sort of feel like I’m preaching to the choir here. You’re all converts. You all recognize the needs of the migrant worker, the need of the monarch, the needs of the bat. We need to break out and talk to the other side.”

The Monarch Butterfly and Pollinator Festival continues with events on Saturday and Sunday. Find the full schedule here.

Jackie Wang covered local government for the San Antonio Report.