Monarch butterflies have been declared endangered. What can we do to save them? Ayesha Rascoe speaks with conservation biologist Karen Oberhauser about why the migratory monarch butterfly was just declared endangered, and what can be done in response.

Monarch butterflies have been declared endangered. What can we do to save them?

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Millions of monarch butterflies make an extraordinary migration journey from across the country to Mexico each winter. The gorgeous insects have been facing external threats to their natural habitats and food sources for decades. And on Friday, the International Union for Conservation of Nature added the migratory monarch butterfly to the endangered species list. Karen Oberhauser is a conservation biologist who researches monarch butterfly populations and migratory patterns. She was a part of the team that made that assessment, and she joins us today. Welcome.

KAREN OBERHAUSER: Thank you, Ayesha. It's great to be here.

RASCOE: Hadn't I heard that there were more monarch butterflies around in certain places?

OBERHAUSER: Yeah, there have been a couple of recent reports that have shown increases of monarchs in some areas, but it's still very low.

RASCOE: So what are the threats to monarchs at this point?

OBERHAUSER: The main two threats come from habitat loss and weather. And if we think of monarchs, monarchs have this incredible annual cycle, and those butterflies need habitat throughout this whole annual cycle of breeding and migrating and overwintering in Mexico. We know that the population used to use milkweed plants that grew in corn fields and soybean fields. And then as farmers had access to genetically modified crops that meant that they could spray Roundup without killing the crops, all of that milkweed disappeared. So that was a big blow to monarchs. But we also know on top of that, weather plays a big role. So, for example, one storm can wipe out 70% or 80% of the monarchs.

RASCOE: What has been done to address shrinking populations?

OBERHAUSER: So people are doing a lot. They're putting in habitat, and this is happening on small scales. Departments of transportation, both on a federal and state and county level, are putting in habitat along roadsides.

RASCOE: When you talk about people creating habitats, like, what does that actually mean?

OBERHAUSER: So monarch habitat basically requires two things. It requires the food for the larvae and for the adults. And the caterpillars only eat milkweed. So I would encourage people to figure out what are the native milkweed species in their area and plant as many of them as they can. And the other thing that's key is nectar plants because the adults drink nectar from many species of flowers. And finally, people should not use pesticides because insecticides will kill not only harmful insects but butterflies and bees and good ones as well.

RASCOE: And what policy wise needs to happen to make a difference?

OBERHAUSER: You know, in terms of policy, the Farm Bill can make money available to farmers to put their land - to set it aside for conservation.

RASCOE: And the Farm Bill, for people who may not know, is this big, huge package about agricultural interest that goes through Congress every few years or so.

OBERHAUSER: Exactly. So there's a lot that we can do that would incentivize farmers to pull some of their land out of production and to really provide a societal benefit.

RASCOE: How can people - like, if they want to help monarch butterflies, what can they do?

OBERHAUSER: Yeah. So besides creating habitat, they can also support organizations that are protecting habitat. But also people can get involved with the monarch monitoring blitz that's coming up from July 29 to August 7. And this is an opportunity for people all over North America to report sightings of monarchs. So...

RASCOE: Oh, that's fun.

OBERHAUSER: If you see it, you report it. So in the United States, you can report it to a program called Journey North, which is something that we run out of the University of Wisconsin-Madison Arboretum. And the final thing that people can do now that you've heard this interview, you are an expert on monarchs, so you can spread the word.

RASCOE: That's Karen Oberhauser. She directs the arboretum at the University of Wisconsin-Madison, and is the founder and director of the Monarch Lava Monitoring Project. Thank you so much for talking with us.

OBERHAUSER: Thanks for having me on. It was fun.

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