Monarch Butterflies Thrived in Wisconsin This Year

The colorful monarch butterflies are just starting to make their 3,000-mile journey across North America.

The flutterers spend the fall and summer living, breeding in and passing through Wisconsin. But the head of a local monarch monitoring community group said they’d soon begin their journey to overwinter in Mexico.

Karen Oberhauser is the former director of the University of Wisconsin-Madison’s Arboretum and cofounder of the Monarch Larva Monitoring Project. She has four decades of experience researching monarch butterflies.

Oberhauser said that at this point in the monarch season, the butterflies are still living and breeding in northern ranges as far north as Canada, but she added that the earliest generation of migrators to Mexico are now about halfway to their destination.

She highlighted a monarch migration tracker site that maps the butterflies through community inputs as they make their way thousands of miles to the forests of Mexico.

“I just looked at those maps and I see some monarchs are showing up now in roosting sites way down in Kansas and even a little bit further south right now,” she told WPR’s “Wisconsin Today.”

In the 2023-24 season, monarchs nearly hit an all-time population low, according to the World Wildlife Fund, or WWF.

This year, Oberhauser said she expects to see numbers rising due to the region’s higher rainfall and lack of drought. But the total population remains at risk from climate change, pesticides and habitat loss.

WWF reported that monarchs covered 4.42 acres of Mexico’s forests last year. That’s down from the nearly 45 acres covered in 1996-97.

On “Wisconsin Today,” Oberhauser talked about her career in monarch research, building communities for monarch preservation and the state of the monarch season.

The following was edited for brevity and clarity. 

Kate Archer Kent: I can’t imagine how exhausting this journey to Mexico must be. How do they survive it? 

Karen Oberhauser: They have built up fat stores in their bodies as caterpillars. It’s really important that their nutrition as caterpillars and what they eat in their milkweed plants, they use to grow and develop. But they also store fat. They produce fat that they store in their bodies as caterpillars, and then as they’re migrating, they’re drinking a lot of nectar. They’re actually a little bit heavier when they arrive in the southern part of the United States than they were when they were leaving up here. They’re getting a lot of nutrition along the way, and that’s because they need to build up enough fat to keep them alive during the wintertime when they can’t eat very much.

But another thing that they do, is they fly really smartly. If you watch a monarch migrating, they spend most of their time soaring instead of using powered flight. Powered flight is like a bird flapping its wings really hard, and soaring is when they’re just moving through the air without flapping their wings, which uses a lot less energy. These monarchs, as they’re migrating south, are taking advantage of air currents and just soaring as much as they can to save energy.

KAK: They nearly hit an all-time low in the 2023-24 season. What has happened to monarchs? 

KO: Well, a lot of things are happening to monarchs. It’s like a lot of other species. They’re suffering a lot of inputs that are causing their populations to get smaller. The biggest one for monarchs, we know, is habitat loss, mostly breeding habitat loss. There just isn’t as much habitat available to them as there used to be. But they are also impacted by insecticide use, both agricultural insecticides and insecticides that people use in their yards to control insect pest populations. Most insecticides are broad-spectrum, which means that they kill everything, not just the target insects. There’s habitat loss, there’s pesticide use.

Climate is another big factor. Because monarchs are cold-blooded, they’re completely dependent on the weather, and if it’s too hot and dry, it’s not good for their milkweed plants, and the monarchs live shorter lives when it’s hot. The population is lower in a hot, dry summer. But on the other hand, if it’s too cold and wet, they don’t do well, so they’re kind of like Goldilocks —  just perfect in the middle.

KAK: This summer has had such large amounts of rainfall compared to previous years. Is that a plus then for the monarchs? 

KO: Yes, this summer has been good for them. And it’s not just Wisconsin, it’s mostly through their entire breeding range. In fact, if you look at a drought map, you can see that there are very few spots in the whole United States that are under severe drought right now, unlike last year. It was interesting this year, when they first came back to Wisconsin in late May and early June, everybody was saying to me, “We’re just not seeing any monarchs. We’re not seeing any butterflies. We’re not seeing any insects at all.”

But then, because we had a relatively benign June with plenty of rain and it didn’t get too hot, the drought abated throughout the whole state and monarch numbers started going up. We saw a lot more monarchs during the second and third generations in Wisconsin than we did in the first generation. So that’s one of the things we look for in a year, how much the numbers increase from the beginning to the end of the summer. And this year was great. I went from people calling me and saying “I’m not seeing any monarchs,” to saying “I’m seeing lots of monarchs.” That’s a great sign.

KAK: How much impact might butterfly gardens or native plantings have on monarch survival? 

KO:  Monarchs can use very small habitats. It’s not like a wolf that needs huge areas of land in order to live and survive. Monarchs can come into somebody’s garden that might only have a few flowers and 10 milkweed plants and lay eggs on those milkweed plants. And the eggs can develop into adult butterflies. Adding as much habitat as we can in any kind of space will benefit monarchs. Of course, if you had a choice between a tiny garden and a huge area. It would be better to do the huge area as a monarch habitat. But the tiny garden can still make a difference, and if we have lots and lots of tiny gardens, it can add up to a huge habitat.

Listen to the WPR report

Monarch butterflies thrived in Wisconsin this year, researcher says was originally published by Wisconsin Public Radio.