How Are the Insects Doing?

: van Klink: The whole period over which we have data and some extreme cases. It goes back to the 1920s, but in most cases it starts in the 1990s. For this entire period, humans have been affecting the environment in a very, very extreme way. So we do not have a baseline what the environment would have looked like in the absence of humans. So we don't know what is natural fluctuation and what is not. What we do know is that there is a very strong declining trend in most locations in the world that has been going on, as far as we can tell, at least since since the start of recording. And we don't even know what happened before that.

00:00:45: Hahn: Welcome to Inside Biodiversity. This podcast is hosted by iDiv, the German Centre for Integrative Biodiversity Research. My name is Volker Hahn. I am head of the Impact unit at iDiv. My guest today is Roel van Klink. Roel is a senior scientist at iDiv. He's an entomologist, meaning that he studies insects. In this episode, we will discuss long-term changes in insect abundance. Which insects are declining? Which ones are increasing? What do we know about the impact that humans have on insects? What is causing the declines observed in many places? Is it pesticides? Is it CO2? Or maybe climate change? And what can we do to help insects? Enjoy this episode of Inside Biodiversity. Roel, Great you are here! Let's talk about insects.

00:01:39: van Klink: Yeah, thanks for having me.

00:01:40: Hahn: So, many people think insects are actually a nuisance. Like mosquitoes. Lice. Ticks–even though they're not insects. But you really like insects, don't you?

00:01:53: van Klink: I love insects. I think the only reason why people would hate insects is that they have not spent enough time looking at them because they're really fascinating creatures. They are super diverse. They do all kinds of different things. You can find them everywhere. Um, and these are basically the reasons why I work on insects. And of course, for me, for me, an additional factor is that there's relatively few people working on insects, so there's a lot to discover. And if you have to write expertise and then you can do a lot. There's a whole world out there.

00:02:28: Hahn: Okay. Do you have a favourite insect?

00:02:30: van Klink: Uh, I personally really like leafhoppers. These are little sap sucking insects. They're related to aphids. And some of these species can also, um, transmit diseases to plants. They suck sap from plants. Um, but lots of many of them are really beautiful. And they have an interesting ecology because they are specialised on many of them are specialised on specific plant species and only occur in specific regions. So yeah, that's my favourite group.

00:02:59: Hahn: The the discussion about insect trends and especially insect declines. It got a lot of attention in 2017 when a study came out where researchers looked at insect biomass in protected areas around Krefeld. Can you tell us a little bit about that study and why? What did the researchers find and what did get so much attention? It was in the media everywhere.

00:03:27: van Klink: There has never been so much attention for insects as far as what follows from that study. But the interesting thing is that we knew actually insects were not doing well. Quite long before that, the first real, real big synthetic study was on butterflies came out in 2004, and it showed exactly the same. Most butterfly species in the UK were doing poorly, and then a number of other studies came out. But then 2017, there's one study about insect biomass. Really collected a lot of media attention. And I think a couple of factors contributed that to that. One is that this was about specifically about flying insects. And one of the reasons why this may have resonated with, with the normal people out there is that they could observe this. They could see that on the windshields of their cars when they were driving 40 years ago versus now. There's a lot less insects on your windshield. You don't have to scrape them off every, every couple of hundred kilometres. So that's one thing. Another thing that may have contributed is that, um, these these people in Krefeld from the Krefeld Entomological Society, they are citizen scientists. So they were doing this out of love for insects. They put up these traps and they just measured how many insects they were.

00:04:52: Hahn: So they're amateurs, right? That's basically what it means.

00:04:55: van Klink: They're kind of amateurs with entomologists. This is there's a very, very grey zone. It's not just a large grey zone. It's also very, very different shades of grey. So lots of people who are really good specialised entomologists do not have a formal training or they currently do not work as entomologists, but they are absolute experts. And I would put the Krefeld people in that bucket. They are really good at what they do. They know exactly how to do it. Some of them will have studied biology, but most are currently probably not working as biologists. Um, so that's one thing that probably resonated with people. And the other thing is that at that particular moment, there was just not much going on in the world. There was there was no Covid. Climate change was just barely becoming visible. Uh, it was sort of as in German as they would say, “Heile Welt”. The world was still good and orderly. And for me, trying to picture a study like that coming out now, I don't think it would get half as much attention simply because there's so much other stuff going on in the world.

00:06:07: Hahn: Probably one reason why it also got a lot of attention is that the numbers that they found were quite drastic, so they found a decrease in insect biomass of 75% over 27 years. So that's.

00:06:20: van Klink: Correct.

00:06:21: Hahn: So huge declines in in in biomass and biomass means they just trapped all, all the flying insects and just weighed them as a as a everything together.

00:06:32: van Klink: And that's also something that will resonate more with people than when I say this or that particular species has declined with that much. If you just say the total mass of insects has declined by 75%, that is much more visible Yeah.

00:06:47: Hahn: So. So it didn't say anything about, uh, the number of species, how they would have changed after that study came out. You were one of the researchers who tried to find out. Well, what do we find if we look beyond Krefeld? What are the trends globally? Can you tell us a little bit about the study that you did and and what you found, and also how that would how that still holds today or not?

00:07:11: van Klink: So what for us, I was working, I just arrived at I live at the time, and I was working already with Diana Boler for some years on long term trends of insects. And I was working with John Chase and all of us. We knew there was so much more data out there that had not been evaluated for whether it was declining or not. So for us, it was a little bit surprising. On one side, the enormous amount of media attention it's got. And on the other hand, like there was so much data out there that nobody seemed to be aware of that was just waiting to be analysed. So that's where we started from. And we tried to get as much data together from all over the world as possible. At least ten years of data collection on insects didn't matter which group, where it was collected, how it was collected, it just had to be standardised data for more than ten years. So we collected the data and then we analysed it and it came out that especially for the terrestrial, so the insects living on the land they were in the majority, the vast majority of locations in in sharp decline.

00:08:20: Hahn: So that's like grasshoppers and butterflies, those kinds of.

00:08:23: van Klink: Grasshoppers, butterflies. The what? I bet my, my favourites are leafhoppers, bugs, ground beetles, everything but but the insects living in the water, like dragonflies and also mosquitoes. We count on that because mosquitoes, almost all of them, actually develop underwater. So they spent the vast majority of their lives underwater. They're actually increasing, at least here in Europe and in other Western countries. And the reason for that is probably that the water quality has improved dramatically since the 1970s and before that, at which time it was absolutely terrible.

00:09:01: Hahn: Mhm. So but that's still a very broad view on insects just looking at aquatic insects and terrestrial insects. But if you look more closely there's a lot more heterogeneity. Right. It depends on what species group you're looking at maybe. Where in the world are you looking at. So there's not just this this one single number that tells us exactly what how insects are doing. Right. Can you tell us a little bit more about how how we need to differentiate to, to understand these trends?

00:09:33: van Klink: Yeah. So the difficulty. So we just put everything together, all of these different groups of insects from all of these different locations. And then you get this average decline. But of course it differs among places. But for us was the difficulty that on one location they measured ground beetles and another location butterflies. And then a third one they did, let's say, uh, leafhoppers or grasshoppers or both. And we cannot compare those trends, or we cannot tease apart whether it's a species or taxon, a group of insect specific trend, or a location specific trend, because all of these locations have different groups measured. So that's why we could not do too much with that. And we still cannot say this particular insect group is doing worse than this other insect group.

00:10:29: Hahn: When you look at these trends, is it possible to say how much of these increases or decreases are caused by humans or let's say, unnatural. And how in comparison to how much of that might just be like natural fluctuations of insect population declining and increasing again. Can can we disentangle that?

00:10:55: van Klink: The short answer is no. We actually don't know because we don't have good baseline data. Basically, the whole period over which we have data. And in some extreme cases it goes back to the 1920s, but in most cases it starts in the 1990s for this entire period. Humans have been affecting the environment in a very, very extreme way. So we do not have a baseline what the environment would have looked like in the absence of humans. So we don't know what is natural fluctuation and what is not. And even in locations that are pristine, these are obviously also much harder to sample, let's say the middle of the Amazon where we don't have data from. Um, this is still not a pristine environment. People have been in the middle of the Amazon for at least 12,000 years. They've been affecting it, and therefore we cannot really say what is natural fluctuation and what is not. What we do know is that there is a very strong declining trend in most locations in the world that has been going on, as far as we can tell, at least since since the start of recording, and we don't even know what happened before that.

00:12:15: Hahn: It's obvious that humans have a huge you mentioned that a huge impact on, uh, on ecosystems, at least here in Europe. I mean, you just need to look outside. This used to be all forest. It's not anymore. So we are changing the landscape and the climate a lot. So and this brings me then to to the next bigger question about the drivers of these insect changes that we are observing. Many people think it's pesticides, but there are a lot of other drivers in the in the discussion that might be responsible for some of the declines we are observing. What do we know about that?

00:12:58: van Klink: Um, shockingly little actually. Um, we've tried a little bit to look at. Okay, can we correlate the trends we find? So how steep the decline is in the different locations? Can we correlate that to changes in the environment? Has agriculture increased or declined? Has urbanisation increased or declined in this particular location? And is the trend different there? And for agriculture, we could actually not find anything. And that's maybe also because agriculture did not really change in most of the locations where we looked, at least over this period. If you go back further. Obviously there must be a massive change in agriculture, which probably affected insects, but we don't know.

00:13:43: Hahn: Has the use of pesticides increased over that period of time that you that you investigated?

00:13:51: van Klink: The pesticides have changed. So if we look back further, DDT was a huge thing in the 70s and they stopped using it. So the whole environment must have been sprayed with DDT at that time. And then they stopped using it. And since the 90s. These neonicotinoids came onto the market that you need a lot less of, but they are much, much more toxic. But the the thing the difference between spraying like DDT, which is basically a massive cloud of poison in the, in the, in the atmosphere, um, we know that that spreads, whereas these neonicotenoids are supposed to go into the soil together with the seed and the plant takes up the poison. And any insect feeding on the plant. Uh, is is going to be killed by eating the poison. So it's a it's a very different mechanism. And then this poison is in the soil, but it's not supposed to get out of the soil. So obviously what's happening is that it flows into the waterways. But there is there should at least not be a massive cloud of poison just being sprayed around. Now, there's other poisons or pesticides that people are using that will spray and that cause a spray drift, and they end up in places where we don't want them. But the truth of the matter is, we do not know what effect that has in which quantities outside these agricultural fields. The agricultural fields have been studied quite well. We know what the poison does there, because that's what the the producers are selling. They know they need to know exactly what it's doing. Is it killing the insects? Because that's what it's intended for. What we don't know is the small quantities we hope that are outside these the agricultural fields. Maybe in a nature reserve. Are they accumulating? How much is it? We know it's there. People have found it in all kinds of places where it doesn't belong. What we don't know is what the biological effect of that is. And that goes for actually a lot of these potential drivers. It's also nitrogen pollution. It's carbon pollution. It is different. Different parts of climate change. We just have a very poor understanding what what each of those drivers is contributing to the decline of the insects and how how does that actually work?

00:16:19: Hahn: What's what's that carbon pollution hypothesis.

00:16:23: van Klink: So that's an interesting one. We know for a very long time that when you enrich the air with carbon dioxide, as we do when we burn fossil fuels, that plants will take up the carbon dioxide. That's always what plants are doing. So now you increase the amount of carbon dioxide. The plants will take that up as well. That makes the plants grow larger. So more of that carbon is also stored.

00:16:50: Hahn: It's a fertiliser right.

00:16:51: van Klink: It is a.

00:16:52: Hahn: Spherical.

00:16:53: van Klink: Fertiliser. Yeah. So the plants are getting bigger, but all the other nutrients are normally staying the same, except in the case where you also have nitrogen pollution which comes from agriculture in most cases. So the nutrients in the plants have a fixed level. But the plant is growing bigger, which means that the relative amount of these nutrients in the leaves and in the other plant parts is going to be lower.

00:17:19: Hahn: It's diluted.

00:17:20: van Klink: It's diluted. So it's more carbon, less of the good stuff. It's basically junk food. We're creating junk food for herbivores, and that is not only insects, that is also larger herbivores, and it's also us humans. And we know there's plenty of experiments that have tried this also with crops. And the nutrient content of our crops is declining. So if you're an insect and you especially if you're a baby insect, you cannot move much and your food is getting worse and worse and worse, that's going to have a consequence somewhere. And it's possible that that has a consequence at the population level.

00:18:00: Hahn: Okay. Very briefly, what about climate change? I mean, many people assume that most of biodiversity change that we observe are mostly linked to to climate change. What do we know when it comes to insects?

00:18:17: van Klink: We know actually quite a lot for especially in Europe, we can see lots of Species that used to occur only in the south are are moving north, and that also should mean that the species that only used to occur in the north, or who have to move further north because their their climatic optimum is moving. Um, we see less of that and that's probably just a lag effect. So we know there's a lot happening. What we don't know very well is what is happening at the population level, what is happening when there's a serious drought. As we have seen that over the last couple of years, every once in a while, how does that affect all the different insect species? And from the sum of all of those insect species is just the total mass of insects? Um, it's very difficult to tease that apart, uh, scientifically, but also that is, is a massive gap in knowledge we just cannot estimate very well what, what the contribution of climate change to the decline of insects.

00:19:25: Hahn: Well, apparently there's a lot of uncertainty, especially regarding the drivers of insect change. But also how much of that is what we observe is actually natural, and how much of it is human driven, or is just what we observe now is actually the result of changes that happened a long time ago when humans started to to change the environment. So with all that uncertainty, can we derive measures or policies where we can be more or less certain that this will actually help insects?

00:20:05: van Klink: Yes, I believe we can. So there will be a number of simple things we can do. And and a lot of that has been experimentally proven. We know that if the farmer most the field five times a year. Almost no insect is going to survive if that gets reduced to 1 or 2 times a year. This is perfect environment for for insects. Um, of course, that is completely contrary to the interests of the farmer. The farmer wants to mow the field five times for good reasons, namely, he or she wants to earn money with it. So there we have a conflict, but we know in many cases exactly what something is doing. We there is a lot of experimental evidence as well that if we reduce a certain pressure, then insects will be doing better. What we don't know very well is the long term effects of that. So usually what you see for in the in the case of reduced grazing or reduced mowing, which I have a background in, is that insects will explode in the first years, they will love it. The the number of insects in the first few years is going to be absolutely enormous. And then over time that seems to decline. And that's the same for restoration projects. In the first year, you find enormous numbers of insects the first few years, and that then declines. And we do not have a very good understanding of why that is. And and that makes it really problematic to really come up with good measures for, um, for long term, uh, helping the insects on the long term.

00:21:50: Hahn: Yeah, but that's tricky also because if you mow less, you will also have less yield, and you will need more land to produce the same amount of food or feed that needs to happen somewhere. So the land footprint then would increase. So as you already hinted that there's a lot of there's trade offs, right? Exactly. You can have more insects on that field where you mow less than you used to, but the yield needs to to come from somewhere you will, you might have to to do more agriculture in other places.

00:22:29: van Klink: That's correct. And that's that's always going to be the trade off. Um, I see I see a very simple solution for that. And that is not feeding so much of our food that we produce to animals. It's a very inefficient conversion. It's like you need to put ten times as much food into a cow as you get out as a steak, let's say. And um, so that's if we just reduce the, our livestock by, let's say, 90% all of that land, what's now being used for feeding that livestock will be available to grow food for humans. It's not exactly that simple, because most places where we traditionally were having livestock were the places where we could not do. Uh, crop. Uh, crop growing like in the mountains and locations that are very wet, locations that are very dry, locations that are just very difficult to to do crop. Um, crop cultures. Um, so it's not as simple as that, but the current situation is that we are growing massive amounts of food with no other purpose than feeding it to our livestock, and we cut down rainforest to grow soy that then gets transported to Europe to go into a cow. And at the end a small steak comes out, whereas probably half a rainforest was cut down for that one steak.

00:24:08: Hahn: So for the individual, that means really If you want to help insect eating less animal based food is a rather efficient way of doing that. Correct?

00:24:22: van Klink: That is absolutely advisable also for your own health, but most of that's going to happen somewhere else. And of course, it's not that simple because it really depends on what the farmer is doing on the field and what kind of food goes into the animals. If then. Yeah, it's it's it's actually very complicated. But there's also things that we can do ourselves. Right. We can have a garden that is not just based on like the worst example is these, these these stone gardens, shelter garden, they call it in German where there's basically no green. That is absolutely catastrophic for all wildlife. Another good thing you can do for insects is having native plants in your garden. So most of the the the imported plants that are not native to Europe will feed very few insects because these insects are insects are not adjusted to this kind of food. The other risk with that is that you bring in insects that you don't actually want. We have massive problems with invasive species and most of them come in with plants, many ornamental plants, but also crops. Um, so by just having a more biodiversity friendly garden, we can already do a lot. And then also putting pressure on our governments to do more environmentally friendly management of the green spaces is going to help more biodiversity friendly, uh, road verge management. And in that way, we can actually do something really concrete for insects.

00:26:02: Hahn: I want to come back to the science before we close the conversation. The things that you have told us about trends that we observe. The drivers that that we think may play a role is all of what you said uncontroversial amongst your colleagues, or what are the most controversial things that are heavily debated in the field?

00:26:30: van Klink: I think there is remarkably little debate, actually. So I think by now it's well-established that insects in most places are not doing well. They are declining. There's some controversy about how much the decline is. There are some people who believe it's absolutely catastrophic, and we're looking at 70, 80% decline since the 90s. My own research of putting all these data together shows it's more in the realm of 30 to 40% since the 90s, which is still a lot. It's but it's not 90%. Um, and I fear that that's also a little bit ideologically driven debate of …

00:27:15: Hahn: We're not talking about like like we mentioned before, we're not talking about number of species, but abundance.

00:27:20: van Klink: Total total abundance. Yeah. Of total abundance of biomass. Just the sheer number of insects and the number of species has to be related to that. That is mathematically almost impossible not to be related. And we also tested that a bit in one of our papers. So the amount of decline that is maybe where there is a little bit of controversy and then there will be maybe a person here or there that just believes that there's no decline at all. Um, but I've, I've had haven't heard that argument in ages.

00:27:55: Hahn: Are insects doing worse than other organisms?

00:28:01: van Klink: This is a good question. I personally doubted. But there is. Actually we can look at this different database called BioTime. So that's a big database that looks at everything from zooplankton to birds to mammals and also a few insects. And they're on average you don't see a decline in abundances. But for the insects, when we put everything together there, it certainly is a decline. So in that respect, it looks like insects are doing worse than other organisms.

00:28:37: Hahn: For our audience, we had two guests on on the show that work with the like you did. I think with the bio time database.

00:28:45: van Klink: I've taken some of it.

00:28:46: Hahn: Yeah, yeah. But we also had guests Maria Dornelas and Jonathan Chase, who also work a lot with that database for for our audience to those are also episodes worthwhile listening to. So let's wrap this up. What would you like the audience of this episode to remember about insects and insect change?

00:29:10: van Klink: I think the most important thing is that insects are amazing. Just take some time to look at them, to look at what they're doing. They're fascinating lives, the staggering diversity. And by that you can develop a little bit of love for them. Um, the second thing is there's so much left to discover and so much that is needed to discover and to. Few people are actually, uh, making the effort of figuring out what it is that's actually happening out there to the insects and what we can do about it.

00:29:46: Hahn: So more research needs to be done.

00:29:48: van Klink: Absolutely. More research needs to be done. But at the same time, there's also a lot of policy that we can put in place that will be better for insects. But we of course know that there's economic interests that are absolutely opposite to what we need to do for insects and also for birds and the rest of biodiversity. It's it's, in the end, very simple equation that the less we destroy, the better it's going to be for nature. But it seems to be very hard to sell to a politician that maybe there's sometimes we should not do something that's going to be very negative for nature. I've tried it, I asked a politician and there's a hard sell. You cannot do it.

00:30:33: Hahn: It's a complicated world. So many conflicting interests and all have to be balanced. This was a highly interesting conversation. Thanks so much all for being in our podcast Inside Biodiversity.

00:30:47: van Klink: My pleasure.

00:30:49: Hahn: If you enjoyed this conversation, be sure to subscribe! Inside Biodiversity is available on Spotify, Apple Podcasts, and many other streaming platforms.