Science Friday
Hosted by Flora Lichtman
A new study of butterfly populations in the US shows a 22% decline among over 500 species in just 20 years.
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This is Science Friday. I'm Flora Lichtman. Today in the podcast, a sweeping study of a beloved insect.
Because people love butterflies, we're able to get a more complete picture about what's going on with butterflies compared to many, many other insect groups.
You've heard about monarch declines, but new research in the journal Science widens the butterfly net and checks in on over 500 species. And the researchers found that many populations are taking a nosedive. So what's causing the downswing? And is there anything to do? Joining me now to explain are two of the study authors. Elise Zipkin is the Red Cedar Distinguished Professor of Quantitative Ecology and Director of the Ecology, Evolution, and Behavior Program at Michigan State University. And Nick Hadad is a professor of integrative biology, also at Michigan State University in East Lansing, Michigan. Welcome to you both to Science Friday.
Thanks for having us.
OK, top level, what did you find?
So we aggregated all the data that were available across the United States, which was 35 different monitoring programs that collected information about butterflies. And we put that into a general model to look at how are butterflies doing overall? And which species are doing better and worse? And what we found in our big grand model was that 22% of individuals had declined since the year 2000. So what that means is if there were five individual butterflies in the year 2000, there were only four in the year 2020.
We also found that there was about 13 times more species declining than increasing. And only nine of the species across the 342 species that we were able to do individual species level analyses for were increasing. So this kind of paints the most complete picture that we have so far about the status of butterflies in the continental United States.
How did you react to this finding?
It's distressing and saddening. To see butterflies declining like this is, yeah, it's just tragic. And the problem is that first, we see decline over the last 20 years. We don't see an end in sight. The trend is still downward.
Elise?
Yeah, I would agree. I mean, insects are ubiquitous, right? And people don't think about it, but they provide so many services to people and to ecosystems, right? So they're really important for pollination, for crop production. They serve as a resource for food for all other kinds of animals, including birds. And we don't have a lot of data on many insect species, but we do have kind of a lot of data on butterflies in particular because people love them. The data were collected primarily by volunteer scientists who participate in programs and go out on their free time, you know, walking different areas around their house and in natural areas and recording the number of individuals that they see.
And so because people love butterflies and are willing to do this, we're able to get a more complete picture about what's going on with butterflies compared to many, many other insect groups.
Because it would be hard to do this with like a beetle.
Right. First, you would have to do a different kind of data collection with a beetle. You wouldn't be able to just kind of walk outside and see them. But also because people just aren't going to do that, right? So it's nice that, you know, because butterflies are so beloved, we have this amazing resource. And this is kind of giving us the most complete picture of any insect group that's around. So I think it's also a little bit of a warning sign to what might be going on with other insect groups.
So this data all came from regular folks who are just butterfly gazers and entered their observations into a spreadsheet somewhere?
Yeah, mainly. These were data that came from thousands of people and tens of thousands of surveys over two decades to the point where we could get, what, 12 and a half million observations of butterflies that went in?
12 and a half million?
12 and a half million. And like you said, I mean, you can't do this for other insects. And that's the cool thing about this study. Butterflies, like Elise and I could go out this afternoon and count the butterflies on one of these paths and then we'd have our data ready to go in analysis. If Elise and I went to look for other pollinators like bees, we could sweep up enough that would keep my lab busy for the winter, trying to identify them. And so you just can't do that.
Well, maybe we need to build interest in other insects. Maybe butterflies are the gateway insect.
Yeah, I mean, I think that's a really good idea. There's a lot that people are thinking about it for participatory science programs. But also, I would argue, you know, even with the butterflies, so there were 554 species observed in our data, but we only had enough data to do analyses at the species level for 342 species. And so we actually could use even more people, more volunteers, you know, collecting those butterfly data. You know, so for example, one of the longest running programs is in Illinois. They've been collecting data since 1987. And there are people there, individuals who walk these same transects.
So transects are line, you know, basically through a meadow or some natural area, usually near their house. People do that every single week during the spring and summer for year after year. And those kinds of information, those kinds of data are invaluable to us. It's not like there are enough scientists to collect that kind of information. So these kinds of synthesis studies just rely so much on... You know, the data that that volunteers are collecting.
Going back to your question about the gateway, I like to think of butterflies as a new birds. I mean, there's 70 million people that watch birds by having feeders in their backyards. And now we're seeing that butterflies can serve as the same role. People love butterflies and they can very quickly develop the ability to identify them and take data on them. Can they be the gateway? Well, I'd hope so. I think the next types of insects that people could get involved with collecting data on are bees and especially the bigger bees like honeybees and bumblebees. It gets harder beyond that. Many bees are tiny, hard to see, but butterflies are declining and we have no reason to believe
that butterflies aren't good indicators for what's happening to the rest of the insect world. And so we need to know more, not just about butterflies, but how they relate to the great diversity of life that is insects that we think are declining as well.
Yeah, well, we've heard about this insect apocalypse, of course. What is causing the decline in butterflies? Do we know?
So there's kind of three big categories that we think about with insect decline. So that would be climate change, habitat loss, and then pesticide or insecticide use. And Nick worked on a study recently that kind of compared those in Ohio. Nick, do you want to jump in?
Yeah, we, it's been difficult to parse out which is the most important factor. And so we compare apples to apples by getting all the data on land use and climate and insecticides and pesticides in the US Midwest, so Ohio, Michigan, Illinois, and other nearby states. And what rose to the top?
As causing decline is insecticides. And so I really do think that insecticides are in our sights to change usage to try to reverse this pattern that we're seeing with butterflies. And trying to switch to a more positive note.
Good luck.
Yeah, I know. Good luck. But we can make changes just to give a sense for this. In the US Midwest, there's 100 million acres where we grow corn and soy. And every seed of corn that's planted has a coating of pesticides, including these insecticides. So we're saturating our environment every year with insecticides. And that's true even if there's no pest problem. So it's a real problem. And in fact, some researchers, including on our, um, our study, show that insecticides don't benefit corn yield.
And so here we are putting massive doses of insecticides out and yet to no benefit, but in fact, a cost to having to put the insecticides out. You know, we're not saying end use of all insecticides. We're saying be more measured and reduce the use dramatically and hopefully benefit butterflies and the rest of insects.
After the break, is there any hope? What can we do to help butterflies?
What's amazing is the butterflies have a potential to recover in a way that you couldn't see with something like mammals.
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You know, we're talking about big systemic changes. Is there anything meaningful that an individual person can do? Like, we hear a lot about milkweed, but is that meaningful? Is that meaningful for the monarch populations? Are there other things we can do?
Yes. I think there's a lot we can do. One thing you can always do is plant local species. I mean, planting milkweed is great, local milkweed species for monarchs. But there's actually evidence that monarchs and other species do better when there's more mixed species being planted. So the key to this is that you want to look up what's native in your area. There's ways that we could work beyond that, you know, with other local people. So for example, my dad, he lives in Cincinnati, Ohio, and he worked with a local park and brought in different groups, and they set up an area where they were Restored kind of a tiny prairie and a butterfly garden. You know, the idea of thinking about restoring areas, and it doesn't have to be huge areas. That can make a difference, right?
Butterflies move around, so they can find these areas, and that can have a big effect.
When we think about how butterfly populations might rebound, is it an advantage that they have short lifespans?
Yes, absolutely. So, one of the cool things is that insects, unlike vertebrate species, right, with the backbones, insects, they rely so much on weather cues and habitat cues of what's going on right now. So, you know, they produce a lot of individuals, a lot of eggs, and those can all either survive or die or somewhere in between. So, in a really good year, we can get off a lot of individuals. So, what's amazing is the butterflies have a potential to recover in a way that you couldn't see with something like mammals, right? Where they produce their young and take really good care of them for a long time, but they're limited on how many they can produce.
So, yeah, I mean, that's one thing that's kind of exciting about this work is things can really change around. It's not like we are on a doom and gloom cycle and this has to go this way. There is a lot of hope for things to change.
Did you find any populations that actually went up in your study?
So, there were nine specifically that have that have high rates of population growth. And one group of species that I've noticed are increasing feed on grasses. And so, these are a group of small brown and orange butterflies. They're called the skippers. Some of those butterflies feed on grasses that are planted in people's lawns or on roadsides. And they seem to be doing quite well. For some of the species, there's good reason for that. We're planting the food that the caterpillars eat. For others, even if they're feeding on native grasses, they're also increasing. And so, it's something that we want to investigate in the future. Why are some species doing so well?
Yeah, that's fascinating. This is a question that comes from Moth Nation. What about moths?
So first, there's 10 to 20 times more species of moths than butterflies. The best evidence we have, and it's much more limited for moths than other insects, is that they're declining at about the same rate of butterflies. But the way I think about moths is, like you asked earlier, if butterflies the gateway to other insects, well, moths is high up on the list of species that we could know more about, and "we" meaning any of us contributing to the data needed. And how people that are scientists are just trying to get an insect, look at them, is
they put a white sheet up in the nighttime and put a black light on the sheet that attracts moths. And so then the moths are sitting on this sheet, and you can see this great diversity of life. And the problem is that moths are very hard to identify. But I've seen cases in England and in the Netherlands, where there are, I'll say, fewer species, but nonetheless, they put a black light and a camera and use AI to identify two species, all the moths, and then gather data on their abundance. So I see the future of studying moths as right at the forefront because we can take
advantage of new coding technologies to identify and count the species.
They're difficult to identify. I'm hearing that as a challenge.
Yeah, the exciting thing, I should say, is that there are new opportunities to do those kinds of identifications. Before, we would have teams of scientists or undergrads working on that in the lab and trying to identify everything which would, you know, be, as Nick said, would keep his lab busy all summer, right? And so now, with new technologies, there's this ability to do those things more quickly and potentially learn a lot more about groups of species faster.
At least, any last words?
Oh, yeah, I do have last words.
A lot of them.
Yeah, okay. So, you know, I think this research can sometimes bring you down, right? Because we're seeing a lot of loss of biodiversity, loss of butterflies, which are a group of species that people love. But as I move through this, I'm always hopeful because I think that there's a lot of opportunities to reverse these trends. I think we're still at this point where we can really protect biodiversity, and we can do that individually. We need to do that also with the support of our governments making policies. But there is really a lot that can be done. And I think it's, you know, upon us to think about that.
Thank you both for the great conversation.
Thank you.
Thank you, Flora.
Butterfly Nation is going to be very tuned into this. Their antenna are going to be up.
Love that.
Elise Sipkin, Red Cedar Distinguished Professor of Quantitative Ecology and Director of the Ecology, Evolution, and Behavior Program at Michigan State University, and Nick Hadad, Professor of Integrative Biology, also at Michigan State, and they're based in East Lansing. Before we go, we want to pin down your most beautiful butterfly memories, you know, while there still are butterfly memories to have. So, did you have a formative experience hunting for butterflies? Did you fall in love with a butterfly net in your hand? Or fall out of a tree looking at a butterfly roost? Did your pet caterpillar make you want to be an entomologist? Or if you're Team Moth, we welcome all legendary lepidoptera tales.
Leave us a voicemail or text us, 646-767-6532, 646-767-6532.
And that is about all we have time for. Lots of folks helped make this show happen, including
Charles Bergquist.
Emma Gomez. Sandy Roberts.
Robin Kazmer.
I'm Flora Lichtman. Thanks for listening.
Page updated November 3, 2026 · transcript and summary are machine-generated