This photo taken in 2013 shows a male Fender's blue butterfly drinking nectar from a common camas wildflower in Eugene at the Willow Creek Natural Area, which is owned and managed by The Nature Conservancy. In 2023, the status of this Oregon native butterfly was changed by the U.S. Fish and Wildlife Service from endangered to threatened.
Cheryl Schultz/Washington State University
A new study led by researchers at Washington State University showed that butterfly populations in the U.S. shrank by more than 20% from 2000 to 2020. More than 100 butterfly species declined by more than 50% during this period, including nearly two dozen that plummeted by more than 90%. The findings are based on more than 12 million observations of hundreds of butterfly species recorded by citizen scientist volunteers and biologists during surveys conducted in the Pacific Northwest and six other regions across the continental U.S.
Cheryl Schultz is a professor of conservation biology at Washington State University and a senior author of the study. She joins us to share more details and how the public can help with butterfly conservation – including species like the Fender’s blue butterfly, which is native to Willamette Valley and was reclassified from endangered to threatened status in 2023.
Note: The following transcript was transcribed digitally and validated for accuracy, readability and formatting by an OPB volunteer.
Dave Miller: From the Gert Boyle Studio at OPB, this is Think Out Loud. I’m Dave Miller. Butterfly populations across the U.S. shrank by more than 20% from 2000 to 2020. That was the average among hundreds of species that were surveyed, but many species saw much bigger declines, anywhere from 50% to 90%. These are some of the headlines from a new study led by researchers at Washington State University. They did offer slivers of good news – a small number of species whose populations increased, despite the overall onslaughts of climate change, habitat loss and enormous amounts of pesticides.
Cheryl Schultz is a professor of conservation biology at Washington State University and the senior author of this study. She joins us now. It’s great to have you on Think Out Loud.
Cheryl Schultz: Thank you. It’s a pleasure to be here.
Miller: Other studies over the years have looked at population declines of specific species or in areas. What’s unique about this new paper?
Schultz: So what’s different about this paper is a large group of us pulled together all of the studies that we could get our hands on, which look at the data that come from people going out in the field counting butterflies and identifying butterflies, and asking if we put all of those data sets together, what’s going on with our butterflies? And this was really the first study to pull together everything across all of those available data sets.
Miller: The numbers in the study are sort of breathtaking – 12.6 million individual butterflies, comprising over 550 species, were accumulated from about 77,000 surveys of almost 2,500 unique locations. A lot of numbers there, but what comes to mind to me is that this is the result of enormous labors of love by volunteers, tens of thousands uncountable hours of people. I just imagine them with notebooks and binoculars, just walking through fields in Ohio, Oregon and Florida, wherever. I mean, is that what we’re talking about?
Schultz: We are, we are.
Miller: Just tens of thousands of hours of people who love butterflies.
Schultz: Thousands and thousands of hours of volunteers just putting time out in the field, walking transects, walking sites, identifying butterflies. So as you said, there are about 75,000 individual surveys. About 80% of those surveys are what we call public scientists, public citizen scientists, community scientists, who are out watching butterflies and getting to know all the butterflies in the world around us.
Miller: People don’t normally do this for earwigs, for cockroaches or for most beetles. And it does say in the paper that more is known in terms of surveys about butterflies than other insects. How transferable do you think is this data about butterflies to the rest of the gigantic insect world?
Schultz: Well, the reason we started with butterflies is we thought that data for butterflies would be better than any of these other insect groups, as you just talked about. And I suspect that for the rest of the insects, it’s probably at least as bad as we’re seeing for the butterflies. So one piece of what we saw is that we looked at the species that we could actually resolve. There’s about 550 butterfly species in our data set, but we can only look at population trends for about 340 of those. And the rest of those, there’s just not enough data to even resolve what those trends are. I suspect it’s just that much worse for all the rest of the insects.
Miller: What role do butterflies play in ecosystems?
Schultz: Butterflies play lots and lots of roles, so we think of them a lot as pollinators. Bees and butterflies are pollinators of many of our flowers and many of our crops. If you look around the grocery store, many of our fruits and vegetables are pollinated by bees and butterflies that are incredibly important. They’re also the food for a lot of the birds and other wildlife. So if you think about caterpillars that many birds, mice and small mammals eat, those are all the Lepidoptera, the butterflies and moths are a big part of that.
Miller: I gave a short version of this in my intro, but can you give us a better sense for the scale of the population loss?
Schultz: It’s staggering to me. As you said, about 20% loss in the last 20 years. So for every five butterflies you would have seen in the year 2000, we see four now. I think of that also in terms of the individual butterfly species, and it’s just sobering to me. So of the butterfly species that we could look at – about 340 of them – over a third of those, 107 species, we’ve lost more than 50% of their populations in just the last two decades. That to me is sobering.
Miller: Does the data suggest anything, the most recent data, about the pace of population decline? I mean, in particular, I’m wondering if it got worse over the course of the last 20 years, if it’s accelerating?
Schultz: I think it’d be hard to know from what we’ve looked at if it’s accelerating. We use the year 2000 as a starting place, largely because many of those data sets just don’t exist for years prior to that. Really, in the 1990s, we started to see an increase in citizen science groups going out to watch butterflies. Many are part of an organization called the North American Butterfly Association where they go out and count. So we don’t have good data sets of this structure going back more years from that to know what the pace of this loss would have been in the 1980s or the 1960s.
Miller: I mentioned the three huge culprits that have been identified so far for this: climate change, habitat loss and pesticide use. Let’s just take the pesticides as one of them for now. What effect are pesticides having on butterflies?
Schultz: I think all three of the factors you just mentioned are having tremendous losses. Pesticides are coating many of the plants that the butterflies eat … so, the insecticides. Herbicides are causing the loss of many of the plants the butterflies need. So when you spray the herbicides on many of our natural areas, we lose a lot of the native plants and frankly the non-native plants that many of our butterflies eat as well.
Miller: Is this mainly tied to industrial-scale agriculture?
Schultz: It’s tied to everything in our environment. A striking piece of a study we did several years ago was that 20 to 25% of the pesticides that we were seeing were in the non-agricultural uses. So in golf courses and rights of ways, in people’s yards and other kinds of things, and that’s only the pesticides that people are tracking. When you go out and buy pesticides at Home Depot or other big stores, for example, you might not be able to track any of those pesticide uses because we don’t track individual uses, just the large uses.
Miller: How are butterfly populations doing specifically in Oregon or the broader Pacific Northwest?
Schultz: In the Pacific Northwest, our butterfly numbers are dropping but not as rapidly as they are in other parts of the country. We’re losing a couple percent over the last 20 years, as opposed to much larger losses in places that are frankly much hotter and drier than our climate is in the Northwest.
Miller: And is that the reason that you have found so far for the smaller drop, that we are not as hot and not as dry?
Schultz: I think there’s a lot of reasons that perhaps the Northwest is not as extreme. One of those is that much of the data that we collect for some of the butterflies here, when we go and count butterflies, if it’s the middle of summer, many of us like to go up to the mountains. We like to count butterflies in the mountains and the areas that might be farther from agricultural areas, farther from cities and other kinds of things. Many of the citizen science data sets come from areas that are close to where people live, and often those areas are not as close to natural areas, wildlands and so forth. So there’s a lot of factors that contribute to that.
Miller: I noted that there were a handful of species across the country that saw population increases. There were also, making it even more complicated … among some species that had overall declines, they had local population increases. But what are the patterns that emerged in terms of why it would be more likely that individual species would actually be doing better now than they were 20 years ago?
Schultz: So there’s, I think, a lot in different individual species that may help species rebound. And I like to think not just of the individual species, but the capacity of butterflies to rebound. One thing is that butterflies are incredibly resilient and they have a capability of increasing rapidly from small numbers. So when we give them what they need, they can increase quickly. That can be a combination of the food that they need, which might be just putting the foods that they need, the host plants that they need, in our gardens and our natural areas, whether they’re lupins for blue butterflies or milkweeds for monarchs. Also, some of the butterflies have the capacity to have multiple generations per year. So if you can reproduce a few generations per year, you can increase more rapidly than just once a year. And some of those species that we see increasing are doing that.
Miller: Can you tell us about the Fender’s blue? It’s a butterfly we haven’t talked about for a little while, but an Oregon native.
Schultz: Sure. I’ve been working with Fender’s blue since the early ‘90s. It’s an exciting butterfly to work on because it’s one of the few butterflies that we have been recovering. It was listed as endangered in the year 2000, actually. And in 2023, we downlisted it to threatened, which means its populations are increasing. What we’ve done with that is we’ve really replenished the landscape. We’ve replenished the landscape with the plants that the butterfly needs. In doing so, we’ve replenished those Willamette Valley habitats with many, many flowers that they need – lupins, mallows, daisies and other kinds of plants that those butterflies need.
Miller: What else has come from that? I mean, what you’re talking about seems like a landscape-scale intervention that helped bring these butterflies back. What were the knock on effects of that work?
Schultz: So one of the amazing things about working with Fender’s blue is being out in the landscape and working with the landowners. Fender’s blue is limited to the Willamette Valley, which is more than 95% private land. And at the organizations that I work with – U.S. Fish and Wildlife Service, Bureau of Land Management – many of the organizations have programs to work with the private landowners, the partners program, to go out into the landscape and say, “How can we help you? How can we have these benefits both on our public lands, but also help you in the work that you’re doing?” And in doing so, we help our vineyard growers, we help the organizations, sometimes the ranchers and others in those areas, so that they can see the benefits of the work that happens when we improve the natural areas and we improve it for all of us in the landscape.
Miller: Are those programs still happening, whether it’s through the Department of Agriculture or Department of Interior, BLM?
Schultz: Absolutely. So in the last couple of weeks, I’ve been at meetings for Fender’s blue and I was at one yesterday for Oregon Silverspot, which is on our coast. And all of those have grass seeds, plant seeds, wildflower seeds, many kinds of seeds going out into the landscape to improve those habitats.
Miller: In the past, we’ve talked about what people can do to help monarchs – I guess the most famous butterfly that there is – in particular, things like planting milkweed. But that’s just one species among thousands. What else can people do?
Schultz: There’s so many positive things that people can do. I mean, one of the exciting things about working with butterflies is there’s so many ways that people can get involved, whether you’re planting things in your garden to help with butterfly habitat, whether you’re working in school yards or in gardens, in the parks, whether you’re contributing at other kinds of levels to help just overall increase butterfly habitat in the world around us, or doing things that can help reduce the pesticide load. So if you can’t necessarily go out and put stuff in your garden – which, even in apartments, often we can put stuff on the terraces – you can still contribute by supporting organic produce and other kinds of things that will reduce the overall amount of pesticides in the environment.
Miller: The new EPA administrator, Lee Zeldin, said last week that the agency is going to be cutting regulations needed to protect the environment and human health. Do you have a sense for what that might mean for butterflies or other invertebrates?
Schultz: I think it’s really hard to know in a concrete way what that might mean. But overall, to the extent that we see higher pesticide loads, or increasing amounts of heavy metals, particulates or other things that are impacting the environment, those just particulate down onto the plants, the butterflies and to our whole environment.
Miller: Cheryl Schultz, thank you very much. That’s Cheryl Schultz. She’s a professor of conservation biology at Washington State University and the senior author of a new study that collected data showing huge drops in butterfly populations across the U.S.
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