Disappearing Insects Could Trigger Ecological Calamity

12:16 minutes

colored drawings of various insects on yellowed paper
Illustrations from “A history of the earth and animated nature : with an introductory view of the animal kingdom.” Credit: Public Domain/Wikimedia Commons

Decades ago, when ecologist Brad Lister surveyed the rainforests of Puerto Rico, he says there were butterflies everywhere. Birds and lizards too. Sticky traps put out to catch insects turned black, they were covered with so many bugs.

Not so today. That once vibrant forest has gotten quieter and emptier, as many of the insects and the animals that depend on themhave disappeared.

Lister’s study has now been compiled with 72 others in a worldwide report card on the state of insects, in the journal Biological Conservation. Its conclusion is dire: “This review highlights the dreadful state of insect biodiversity in the world, as almost half of the species are rapidly declining and a third are being threatened with extinction.”

In this segment, Ira reviews the report with Lister, and fly expert Erica McAlister of the Natural History Museum of London gives her take on what we knowand don’t knowabout the world’s insect biodiversity, and the uncertainty underpinning the report’s prediction.

Further Reading

  • Read Brad Lister’s full paper on insect declines.
  • Dive into a feature on what dwindling insect populations mean for the rest of life on Earth.
  • Read about the “insect apocalypse.”
  • Learn what happens when we lose frogs.
  • Find out what happened to Puerto Rico’s insect population when temperatures rose two degrees Celsius.

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Segment Guests

Brad Lister

Brad Lister is an ecologist and researcher in the Department of Biological Sciences at the Rensselaer Polytechnic Institute in Troy, New York.

Erica McAlister

Erica McAlister is a senior curator at the Natural History Museum in London. She’s also the author of The Secret Life of Flies (Firefly Books Ltd.).

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. Later in the hour, the liquids that rule our lives. 

But first, decades ago when my next guest surveyed the rainforests of Puerto Rico, he says there were butterflies everywhere. Birds and lizards, too. Sticky traps put out to catch insects turned black, they were so covered with so many bugs. 

Not so today. That once-vibrant forest has gotten quieter, emptier as many of the insects and the animals that depend on them have disappeared. 

His study has now been compiled with 72 others in a worldwide report card on the state of insects out in the journal, Biological Conservation. Its conclusion, and I quote, “This review highlights the dreadful state of insect biodiversity in the world, as almost half of the species are rapidly declining and a third are being threatened with extinction.” 

Joining me to talk about it is Brad Lister, an ecologist and a researcher in the Department of Biological Science at Rensselaer Polytech in Troy, New York. His Puerto Rico work appeared in the proceedings of the National Academy of Sciences back in October. And we have links to his study and the new review up at ScienceFriday.com/insects. Welcome, Dr. Lister. 

BRAD LISTER: Well thank you. It’s great to be here. 

IRA FLATOW: Give us an idea of just how bad this is. 

BRAD LISTER: I don’t think I’m overstepping the bounds by saying it looks worldwide like a catastrophic decline in one of the most important groups of species in the food web. They’re right near the bottom, and a lot of other animals, and insects, and plants depend on them. 

IRA FLATOW: So give us a quick rundown of what this new review study says and what the reason is for the decline. 

BRAD LISTER: Well, there are many reasons depending on what part of the planet you’re in. What the new study, I mean the biological conservation study, was really pointing the finger at a global problem. And that wasn’t clear. We thought it was widespread, but they really had the data to say this is a whole-earth phenomenon. And all the more frightening because of that. 

So they were able to measure rates of decline and a lot of different insect groups from very precise studies. And they found that the rate of decline was astonishing. It was 2.5% per year, overall. And that’s about the same decline we got in the Luquillo rainforest for our more limited study at one elevation in the Luquillo mountains. 

IRA FLATOW: That’s interesting. You studied the interconnectivity of the food web in Puerto Rico’s rainforest. How does the disappearance of insects ricochet up the food chain? 

BRAD LISTER: Yeah, that’s– We weren’t expecting such a dramatic crash of the insect population. We thought it would change. It’s been 30 years or more. But when we saw that there was a 98% reduction in biomass compared to the 1970s, we thought, well, this has got to be having an effect on the insectivores– the birds, the lizards, and the frogs– which were always super abundant in that forest. 

So we started taking a look at long-term data. We had data on the lizards, the anoles lizard populations from the 1970s. And they declined in biomass by about 50%. And there were also data from the long-term ecological research station at El Verde, and that data was on birds, on frogs, and also on other insect groups. So we analyzed that, and everything was in decline. And the vertebrate– the insectivores were in decline in parallel with the insect declines. 

IRA FLATOW: So is the fear here that this is not just limited to one locality you’ve been studying? This might be a worldwide phenomenon? 

BRAD LISTER: Well with regard to rainforests, yeah. I think that’s why people were so astonished and actually frightened by our study. Because there’s so little data on tropical rainforests, and of course they harbor 75% of the world’s species. And this would be yet another insult to the integrity and functioning of tropical rainforests. 

IRA FLATOW: I’d like to bring on another guest with some perspective on what we know and don’t know about the insect world. And why there’s still some uncertainty about the fate of the world’s insects. Erica McAlister is Senior Curator of Flies and Fleas at the Natural History Museum of London. She joins us by phone from a fly conference. Welcome back, Dr. McAlister. 

ERICA MCALISTER: Hello. Thank you. Thank you again for having me. 

IRA FLATOW: Before we talk about the insects study, I understand you’re working with a species called dancing flies at this fly forum you’re at. 

ERICA MCALISTER: Yeah, no. It’s a weekend course where a lot of the fly specialists in the UK all get together. We pick a family of flies to study, and then we spend all weekend trying to learn as much about them as possible. 

IRA FLATOW: The, well, to put it– it’s bug-like, but entomologists have been abuzz this week talking about some issues they have with the latest report. What is the concern? Tell us. 

ERICA MCALISTER: The concern. What with the report, or about what it’s telling us? 

IRA FLATOW: Well, let’s talk about the report first. 

ERICA MCALISTER: Well the report is amazing, because it is the first time a lot of this data has been collated together. So this is great. It’s finally been– suddenly all these little studies have been lumped together. And it’s like, look, seriously. We haven’t been making it up when we’re telling you that things are going wrong. 

What it’s also has done, though, is highlight what we don’t know. And this has been interesting in its own right. So a lot of these studies are looking at biomass, because we don’t know about species richness. And the reason we don’t know about species richness is we don’t know what’s there in the first place. 

So we have lots of issues that we haven’t got long-term data. And that is because people haven’t really been interested in insects. We’ve been ignored by– I mean your previous talker was saying that we’ve got lizard data going back. We can look at bird data going back. We can look at all of these, but it’s very hard to find insect data. 

IRA FLATOW: And– will insect data tell us about what the possible effects of climate change might be? 

ERICA MCALISTER: Insects are going to be better than anything else, because insects are the ones who react. Insects are more– I mean, what I personally, was like, what is shocking about this report is the lack of flies. And obviously, I’m a little biased about the flies. But because the flies are so critical in every part of an ecosystem, to leave them out is just a shocking behavior if you ask me. 

And the thing is, they react really quickly to environmental change, and they’re ecosystem drivers. And they’re so important. And if you destroy in that part of the ecosystem, you’re basically wiping out a huge component of it. 

IRA FLATOW: All right. Brad, you studied insects in the tropics. How comprehensive is our knowledge of how insects in tropical forests are faring? 

BRAD LISTER: Well there’s virtually no other data points. I think there’s one place that we’ve found. We’re looking for more, because we want to follow up on this. So it’s the paucity of data, would certainly be the way to say it. And it’s sad that we don’t have any, because they’re such a crucial part of the ecosystem. So we– It’s a very daunting and very disturbing trend if it’s applicable to other rainforests. Because then we’re really in trouble. 

IRA FLATOW: Dr. McAlister, butterflies, moths, bees, are all in grave danger, according to the new review. But flies, not so much. I mean– 

ERICA MCALISTER: Well that’s because no one looks at flies. I mean, flies have a problem is that they’re really hard to identify. They’re not these charismatic insects that everyone else goes, oh look at the bees that pollinators. Which is unfair, because they are some of the best pollinators. 

There’s just more species of flies that haven’t been discovered. There was a brilliant paper that came out last year in Costa Rica. It was looking at species diversity of flies in a rainforest. And one of the world’s experts, Brian Brown who does Phoridaes, he looked at the Phoridaes there. And they identified 136 new species. Only four Phoridaes, this family of flies, were on the Costa Rican list already. So just showing you how many unidentified species are there. It’s a lot for us to get our head around. 

IRA FLATOW: You know, Brad, it’s been hard to find political consensus for fighting climate change. But at the same time, there is business interest, because you can make money on solar, and wind, and so on. Is there any business case to be made for saving insects? 

BRAD LISTER: Nothing other than the collapse of our food supply, perhaps, is one consequence that might have some economic consequences. Pollination of our crops and also wild plants. We rely mainly on wild bees and other wild insects. 

There’s just a host of ecosystem impacts that insects’ declining are causing on not only the loss of species higher up in the food web, but a lot of these species are symbiotic. A lot of them interact with many, many different plants. And we’ll be literally heading towards a major collapse of ecosystems, apparently globally. They provide the ecosystem services that we rely on us to sustain our existence. So yes, going to be bad. 

IRA FLATOW: Sounds apocalyptic. I mean, so where should we focus our efforts to turn this trend around and try to prevent the wide-scale extinction of insects, Brad? 

BRAD LISTER: Well, look, so much of this decline of insects and the problems with the vertebrates that the World Wildlife Fund pointed out in their report on the Caribbean and Central America, where about 80% of the vertebrates had declined precipitously. 

So it’s really, at the heart of it, is over-exploitation and overpopulation. I think unless we get a handle on those two factors, along with the emissions. But that really comes from our industrial activity, and the way we raise crops and food, and the number of people that we need to support. 

IRA FLATOW: You’re saying pesticides, 

BRAD LISTER: You have to take care of those big– 

IRA FLATOW: Industrial agriculture, and all that kind of stuff that we’ve heard about? 

BRAD LISTER: Yeah, all of that. But all of it emanates from over-exploitation, overpopulation, and our incredibly wasteful lifestyles. 

IRA FLATOW: Erica, your last thoughts on this? 

ERICA MCALISTER: I mean, I will concur with the lot of that. We have to do something quite quickly. Land use change is seen as one of the biggest drivers for species extinction, and the idea that we waste so much land is a really valid point. 

IRA FLATOW: And as far as the insects, can we expect an increase maybe in the house flies, and cockroaches, and things? 

ERICA MCALISTER: Yeah. Since– Species that hang around us, because they’ve adapted to hang around us. They love us. We are wasteful. We are dirty creatures. So they’re going to just benefit for us moving around and doing that. 

But in many ways– It’s like you’re targeting by saying, yeah, we’re going to have some of the horrible flies, and therefore we go get rid of all the flies. And it’s like, well– That’s like saying all the primates are bad, just because of one species. So we have to be slightly careful about that. 

And we also have to remember that a lot of the house flies are important pollinators. So we’re in a mixed bag, what we should expect. 

IRA FLATOW: We need to be re-educated. 

ERICA MCALISTER: We need– Yes. Education is a really big point here. We need to reconnect ourselves with the environment. 

IRA FLATOW: OK. That’s a good last word. Erica McAlister, Senior Curator of Flies and Fleas at the Natural History Museum of London. Brad Lister, an ecologist and researcher in the Department of Biological Sciences at Rensselaer Polytech up there in Troy, New York. Thank you both for joining us today. 

We’re going to take a break and look how much hotter your backyard barbecue will be in a couple of generations due to climate change. We have a map. You can plug your city in, and you can get a prediction of the future climate right where you’re going to be. And it’s going to be different. We’ll talk about the details after the break. So stay with us. We’ll be right back.

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