Q&A: Global Insect Declines Due to “Death by a Thousand Cuts”

David Wagner

COURTESY OF DAVID WAGNER

The Scientist: In the introduction paper you say that insects are suffering from ‘death by a thousand cuts.’ Could you explain what you mean by this? 

David Wagner: There have been about two or three large studies [on insect declines] that have attracted a lot of attention. In every case—and in others—we haven’t been able to pinpoint the causal factor. . . . And I think it’s because of death by thousand cuts in the sense that it’s oftentimes a multiplicity of factors acting, and it’s a different set in different locations, which makes it a very hard problem. But I think where you have lots of anthropogenic activity, people cutting down forests, areas of high urbanization, or lots of agriculture, there’s going to be multiplicative factors involved in the decline of any one [taxon]. And the honey bee or the monarch [butterfly] would be great examples of things where we think there might be six or seven primary factors that are really challenging these animals.

TS: What are some of the biggest threats to insects? 

DW: I think, globally, I’m most worried about habitat destruction, particularly deforestation in the tropics, and essentially that is also agriculture in the sense that many times we’re cutting down rainforest to plant soybeans or some other crop. And climate change. Climate change is the big unknown. . . . In the temperate zone, it’s often just having huge numbers of people; these declines in North America and Western Europe are often in areas of very high human density. . . . We’re pushing Mother Nature into the corners and we’re fragmenting her and marginalizing her and applying pesticides and doing what we can to push nature back. That doesn’t surprise me. But some of the reports that are coming out of the neotropics really frighten me in terms of climate change. And there I’m quite worried that the cloud forests and rainforests are drying out—sometimes only for a few days, but that’s devastating to dry out a rainforest, to expose these plants and animals to physiological conditions they’ve never experienced. But there’s other stressors: there’s pesticides, there’s exotic species, and suburbanization. 

TS: What is the current understanding of what insect populations are looking like worldwide, and how do these studies in the collection contribute to that picture? 

DW: I think the most important thing we do is suggest that it’s much more complex than initially reported, and we made a point to draw attention to many cases where insects are increasing. It’s not like there’s a single rate of decline that is omnipresent around the planet. We don’t believe that anymore. And so some of the early reports were implying that. The review by Sánchez-Bayo and Wyckhuys, for example, they were claiming we would lose 40 percent of all insects within decades. But clearly with climate change and global warming, we’re going to have increasing numbers or at least new species showing up in areas where winter temperatures have limited their distribution. Here in New England where I’m at, we’re seeing a number of new butterflies that were southern and never were established and residing here. And so in cases where you restore habitat, we can still restore numbers and bring populations back from the brink for a number of insects. . . . There’s hope in terms of our own personal actions. 

But we also found that in areas of high human activity, we have species declining at one to two percent [annually] . . . and that’s really catastrophic. It’s hard to convey to people how important one to two percent is. It doesn’t sound like much, but that’s ten to twenty percent per decade. Over a couple decades you could lose a third of your insects. . . . But it’s not uniform across the planet, and there are places where they’re declining much faster than one to two percent, and we’re especially worried about the tropics.

TS: How would you like the findings in this collection of studies to be applied?  

DW: I think at least five of the contributions mentioned things that we could do going forward. . . . There is a really nice paper in the collection by Akito Kawahara and his coauthors that list eight things that individuals can do to help the plight of insects, so that was an important piece in the collection. But other authors as well talk about maybe making agriculture a little bit more friendly, and the introduction to the collection also mentions things that are looking up for insects in terms of funding and policy. One [idea] I love is kids and parents getting together in a small section of the yard they let go ‘wild’ [to] create a nature observatory or a tiny nature preserve that’s just big enough for a lot of bugs. 

TS: Was there a study in the special issue that you found most striking, and why? 

DW: I thought one of the more important studies in the collection was Matt Forister’s study on the role of climate change in insect declines. He had some very good data from out west [in the US] and some surprising results about one of the drivers that was completely new, that no one had discussed. Warmer temperatures at night and drier conditions in the fall are challenging mountain butterflies. . . . So many people, when they think of climate change, think of global warming, and they almost synonymize climate change with global warming. But . . . climate change also means more droughts of longer intensity, climate change means more fires like we had in Australia and the Amazon and horrific fires in California, climate change means less snow to insulate these animals over the winter, and climate change means that soils are drying out. The very place where these things were maybe diapausing or holding over for the winter now don’t have enough moisture to sustain them, so there’s all kinds of aspects of climate change that have not even been measured yet that are affecting biodiversity, and I think that message comes out really strongly in Matt’s paper and that’s enormously important.

One of the studies that is really exciting and new is Dan Janzen’s paper; it’s actually the Costa Rican government’s interest in barcoding every organism in Costa Rica. Basically, they want to get DNA from every single organism in the country. I think it’s a hundred-million-dollar effort over ten years to map out the tree of life and to make this knowledge available to every citizen, every school child, and every weekend naturalist in the country to make them more aware of the tremendous biodiversity in their forests and in their mountains and have them be stakeholders and owners of this tree of life. And so that’s a very new concept, basically it’s about generating bioliteracy so that people know and care about these creatures that they’re sharing their country with.

TS: What are some of the challenges of researching insect diversity and answering this question about global insect declines?

DW: The big challenge is that we don’t know enough. And it’s particularly true of the tropics. I think maybe eighty percent of all insects are in the tropics, most of which haven’t even been given a name, and it’s hard to protect things that are unknown and unstudied. There’s just so much diversity and so little data that we don’t know what’s going on there. That’s actually a pretty frightening unknown.

Insects are very difficult to study in the tropics in the sense that they’re hyper-diverse and they tend to be small and we don’t even have the taxonomy to really get started there. Another thing that makes it hard to understand how fast they’re increasing or decreasing or whether or not they’re fine is that they go through these wild population cycles from year to year, they have these boom-and-bust lifecycles. That makes it really hard to see a one to two percent erosion on a yearly basis.

TS: What do you see as the promising technologies or initiatives going forward for understanding these questions about insect declines?

DW: A lot of wildlife biology is moving towards automated data collection. And then moving also to molecular methods for insect identification because there’s so many [species] and it requires experts [to identify them] that if we just move it to molecules, we can collect data on everything, even in a rainforest. One of the things I think is really exciting is that the phone apps are getting so good for insect identification that now even a fourth grader can make very important discoveries and get the name of something and have that information get uploaded into a database. So we have much more community involvement, orders of magnitude greater in the last ten years than any time before because there are so many really great identification guides for people that just have a little time on weekends or want to know about the nature in their backyard or they’re grounded because of COVID. . . . I think there’s a new group that just started two years ago to identify caterpillars together, and they’re all talking together on Facebook, and it’s got 13,000 people now. I mean, that is a new human culture or new phenomena, it hadn’t even existed ten years ago, so we’re going to see massive amounts of community-collected data by children and weekend naturalists and backyard biologists and lawyers and doctors and gardeners.

Editor’s note: This interview was edited for brevity.