Flight simulator for moths reveals they navigate by starlight

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0:57But now the data's... I find this not only refreshing, but at some level astounding. Nature.

1:11Welcome back to the Nature Podcast. This week, the moths that are guided by the stars. And how human populations expanded into new ecosystems 70 ,000 years ago. I'm Benjamin Thompson. And I'm Nick Parchichow.

1:33Bogong moths can use the stars to navigate, according to a new study in Nature. Few animals are known to use the stars to find their way. Humans, famously, have used them throughout history, and some migratory birds are thought to be able to. Other than that, the list isn't very long, as far as we know. When it comes to insects, only dung beetles are thought to use the stars to navigate, but even then, only over short distances. Bogong moths, though, are insects that travel great distances. Each year, an enormous number of these moths migrate across Australia to a very specific location that they've never been to, and later they make the return journey.

2:20Clearly, being able to find their way is of great importance to these insects. Evidence suggests that bogong moths use the Earth's magnetic field to help them find their way, but now the new study shows that they have another tool in their navigatory arsenal, the Milky Way. I caught up with study author Eric Warrant to find my way through the study. I started by asking him to tell me a bit more about these curious moths. They're a very nondescript little moth that doesn't look much different than any other brown moth most people are kind of aware of, but it has a quite remarkable natural history compared to most moths.

3:00This moth is a long distance migrant at night and it's able to find its way from its breeding areas in spring about a thousand kilometres to a place it's never been before, which are an assembly of alpine caves in Australia's highest mountains in the extreme southeast of the country. And these moths have come from all over southeastern Australia, about four billion of them. And that's obviously a really long trip. Why is it that these moths are doing that? We don't know exactly, but it's very likely that they're attempting to escape the coming heat in the breeding areas where they've departed.

3:36And these areas are in semi-arid areas of southeastern Australia. They can get very, very hot in summer. And we do know from preliminary measurements that they don't tolerate heat so well. So at some point during their evolution, they've developed this strategy of leaving these areas and going to the coolest place that exists in Australia in summer, which are high alpine areas. And so, as you said, this is a 1 ,000 kilometre journey that they've never done before. So I guess the question at the centre of your paper is how do they find their way? What have been the ideas before your study on how exactly they might have done this?

4:12Well, I must admit we got our clues about how they might be doing this from nocturnal birds that migrate long distances. For instance, European birds that travel from Europe to Africa every year. we know already that they use the Earth's magnetic field and they also use the stars. And we had already found about eight years ago that the Bogong moth has a magnetic sense in a separate set of experiments. And so we started to think, well, maybe they're able to use the Earth's magnetic field. But we also, in those earlier experiments, realized that the magnetic sense was used together with visual landmark information.

4:48And we were very curious, really, about what kind of visual information these moths could be using. and the stars became an obvious thing to investigate. And so how do you go about determining whether they're using the stars to navigate? Do you just watch them and see if they look at the stars every now and again or how is it done? Well, the way we did this experiment actually was in very controlled conditions. We built a lab in Australia where we did these experiments and we captured the moths during their migration in the spring on their way to the mountains and in the autumn on their way from the mountains just by using a lab with a big sheet in a tree in the wilderness.

5:23And we transferred the moths that we caught to a so-called flight simulator, which is just a kind of a cylinder that sits on the table. And we suspended the moth in the middle of this cylinder on a long, thin axle that allowed the moth, once attached to this axle, was able to fly vigorously in any direction it wished. And then above the moth, we actually projected an image of the starry night sky using a projector, a highly realistic image of the sky outside the lab on the day and time of the experiment. And in order to make sure that the moth was not using the Earth's magnetic field as its cue for navigation, we had the whole arena surrounded in a set of three-dimensional Helmholtz coils, which allowed us to completely control the Earth's magnetic field.

6:11and in this particular experiment actually get rid of the Earth's magnetic field entirely. So there was, in fact, no field present around the moth. And then we just simply watched what the moth did under the natural sky. Which way did it fly? Was it confused or could it fly in its appropriate migratory direction? And we found that moth after moth after moth flew in its appropriate migratory direction. And if we rotated the starry night sky 180 degrees, they turned and flew in exactly the opposite direction. and if we took all the stars and randomly distributed them across this projection screen then the moths were totally disoriented and that was what made us realize that they could actually see the stars and use them as a compass to find a micro tree direction relative to north.

6:56I wonder though the night sky changes quite a lot the stars aren't always visible it could be cloudy as the earth moves the stars move relative to it so how is this a good cue for them to you know navigate and find their way that would be a bad idea to only have that single compass because as you say if the stars are completely covered by cloud then that information is gone and they would be disoriented but we do know now that when we actually had the moths in our flight arena but this time not in the lab but up on the hill behind the lab under the natural australian sky then we discovered that they were able to orient under the natural stars in the right direction as expected.

7:39But even on nights where the stars were completely covered by cloud, they could still do it, which implied that they were using something else as a compass. And because we already knew that they had the ability to detect the Earth's magnetic field, we deduced that it must have been the Earth's magnetic field that they fell back on when the stars were covered by clouds. So what we effectively found was that the moths have two compasses, a stellar compass and a magnetic compass and that they use both and if one disappears for whatever reason because of cloud for instance covering the sky then they can default to the other in this case geomagnetic compass.

8:16And no offence to any moths listening but they have quite tiny brains and I wouldn't have thought the best eyes to be able to see the stars so did you figure out how they were actually using their cues despite these limitations? Yes that's a very good question because the eyes as you say, are very, very small. And this limits how many stars they can actually see, because the number of stars in the nighttime sky that you can actually see is determined by the size of your pupil in the dark. And in the dark, our pupil is about eight millimeters across, and it's about a tenth of that in a Bogong moth at night.

8:54So the number of actual stars they can see is extremely low. But in comparison to our eyes, the optics of the Bogong moth eye are built in such a way that the extended world, that is to say the world all around us that we normally look at, is much, much brighter for them than it is for us if we look at the same scene. And because the Milky Way is effectively an extended object in the sky, this means that the moths are very likely able to see the Milky Way much more vividly and brightly and in much greater detail than we can. And we think that this may be key to the compass, actually, because if you see the Milky Way in the southern night sky, this is very different to the northern hemisphere, but in the southern hemisphere, the Milky Way is extremely prominent, and it varies in its intensity, actually, so that it becomes brighter and brighter the more southwards you look into the Milky Way.

9:49And this gradient of intensity may be part of the mechanism by which the bogle moth is able to use the night sky as a compass but that's still a speculation we haven't investigated that yet in detail and do you think this is just something that these moths have or what you found here do you think it could be found in other insects or other animals absolutely we think this of course and we already know for instance that birds very likely use a very similar compass mechanism to navigate between europe and africa but when it comes to other insects there's no reason why this wouldn't be a useful thing for other nocturnal moths that migrate long distances to use, even though the vast majority of moths that migrate do so from one broad latitudinal region to another, typically between north and south, one direction or the other.

10:38But nonetheless, to find that southward or northward direction, it would be very useful to employ compasses just like the bogong moth. That was Eric Warrant from the University of Lund in Sweden. For more on that story, check out the show notes for a link to the paper. Coming up, evidence that humans moved to live in many different ecosystems across Africa, shortly before migrating out of the continent. Right now though, it's time for the research highlights with Dan Fox.

11:09Nigeria's pangolins are under threat, mainly because they're considered delicious. Pangolins are among the most trafficked animals in the world, in part because their scales are used for traditional medicine in Asia. Nigeria has become a global hub for pangolin trafficking, but the reasons why people are going after these animals has been unclear. To better understand why hunters poach pangolins in Nigeria, researchers interviewed 809 hunters and meat vendors in the country's southeastern region. They found that scales were not the main driver. Instead, 98 % of the pangolins caught were used for meat.

11:53The animals were either eaten by the hunters or sold at a local market. The survey respondents also gave pangolin meat the highest palatability score of all listed meats. They suggest that conservationists should focus more on shifting local behaviours through education and food safety programs rather than concentrate on cracking down on scale trafficking. Find that research in Nature, Ecology and Evolution.

12:24The galaxy Andromeda and our Milky Way have long been thought to be on a collision course, but some researchers have now cast doubt on this intergalactic merger taking place. The Milky Way and Andromeda are the two largest galaxies in the cosmic neighbourhood called the Local Group, meaning that their gravitational pull dominates the region. But roughly 100 smaller galaxies in the area also exert their own gravitational pull. Researchers modelled the dynamics of the Local Group, including the third and fourth largest members, and found that one of their trajectories may pull the Milky Way sideways as Andromeda approaches.

13:06giving a 50 % chance that the collision will be avoided for at least the next 10 billion years. Collide with that research in Nature Astronomy.

13:25Next up on the show, new research suggests that Homo sapiens massively expanded the range of ecosystems they lived in, not long before our species made its first successful migration outside of the African continent. Genetic studies indicate that contemporary Eurasian individuals can trace a huge amount of their ancestry back to a small group of homo sapiens that migrated out of Africa around 50 ,000 years ago. But this wasn't the first time our species attempted this journey. There's lots of evidence of human activity outside of Africa long before this, but none of these populations appear to have gone the distance.

14:07A big question is, why? There are many competing ideas, but to help shed light on this question, a group of researchers have a paper in Nature in which they've combined data from climate models with information gained from archaeological sites across Africa. Their findings suggest that in the lead-up to the successful migration, humans expanded their habitat range across Africa, a move which may have helped set them up for their later travels. To find out more about the work, I spoke to one of the team, Eleanor Sherry, from the Max Planck Institute of Geoanthropology in Germany. I asked her to lay out some of the other ideas as to why the migration 50 ,000 years ago may have been successful.

14:53Some of the hypotheses that have been proposed are very difficult to prove. So things like, oh, maybe grandparents were living longer and this affected, you know, survivability of children and there was a population increase. Or, you know, other ideas that have been proposed, there was some kind of technological breakthrough, but no one's ever been able to find any evidence from the archaeological record that looks profoundly different beyond Africa as opposed inside Africa. And some studies also spoke about potential population expansions within Africa before 50 ,000 years ago, which was sort of interesting.

15:24The data from the genetic record potentially reflects this. And yes, one of the reasons that some folk think led up to humans migrating out of Africa 50 ,000 years ago is that they moved to live in a bunch of different places and different ecosystems. And perhaps in some sense, this provided the skills or the knowledge, obviously hard to know, that ultimately allowed for successful migration out of the continent. And this is central to your work. You're looking at the expansion of modern humans, homo sapiens, into new ecosystems, new niches within the continent of Africa, right? Yes. And this ties up with some of the work that came out of the genetic studies that spoke of population movements at exactly the same time.

16:05And to look for more evidence that this expansion preceded outward migration, you've combined archaeological work with climate work looking specifically at the time 120 ,000 years ago to 14 ,000 years ago why have you done this? Basically to be able to understand habitats and niches we need to have a rounded picture from climatic variables we need to know about vegetation the bios that were present because these also shift through time right so for the whole 120 ,000 years a patch of rainforest or always a patch of rainforest there are shifts because there were changes in rainfall, there's changes in temperature.

16:38So you have this dynamic shifting environment. And we then have humans moving around. For the archaeological data, what we have is we know where archaeological sites were, and we know how old they are. So we can root those sites within particular ecosystems through time using the climate model, and then use that to understand how people may have been shifting their environments over a long period of time. So you've got this situation then where you've got physical evidence of human habitation and you've matched that up with your modelling of what the climate may have looked like in different periods.

17:12By combining these, what do your results show about how humans might have moved around before they migrated out of the continent? What we see from that work is that there is an overall niche space and by that I mean there's an overall space in Africa suitable for human habitation and that's going to exclude extremely arid deserts, you know, places like that. That background niche space and the human exploitation of various niches in Africa track each other pretty well until 70 ,000 years ago, where we see this decoupling. We see the overall niche space decreasing, but we see human niche space expanding.

17:44So for example, from the studies, it's obvious that people like ecotonal environments. So these are border areas between very different ecosystems. So you might have a grassland and then you have a forest and And the area in between them is sort of this ecotonal mixed environments. And, you know, people did exploit those environments in the past because you can get mixed resources. But it looks very much like overall there's a population in Africa. After about 70 ,000 years ago, we see a much more intensive engagement with different ecosystems. That speaks to a need and an ability to be able to do so that we just don't see in the record before.

18:23So what you're saying is that before 70 ,000 years ago, humans were moving around areas that were perhaps the most habitable between forests and savannah, for example. But as you get closer to this 70 ,000 year mark, they suddenly expand where they live and live in lots of different environments. Yes. And I sort of want to emphasise that it's not like before 70 ,000 years ago, people were just exploiting grasslands. They did exploit different ecosystems. And we know they did. We have archaeological evidence for it. But the intensity of exploitation changes around 70 ,000 years ago. And what does your evidence suggest may have caused this?

18:59Because you're looking at archaeological evidence and climate modelling evidence. Is there something in one or the other that suggests why this might have happened? So if we look at the climate, and we look at, for example, climate variables that represent preferred human habitats, so certain temperature, certain rainfall, etc., we can see that obviously this is very dynamic over time in Africa. Sometimes these spaces with these suitable variables increase, and sometimes they decrease. And after 70 ,000 years ago, we see a decrease. So it is not good times for those human populations in Africa.

19:34And this is somehow leading them to adapt. And this form of adaptation means that they are moving and exploiting into environments that perhaps they had limited experience with before, exploited in a limited way before, but they're fully engaging with these environments. And your evidence then suggests that homo sapiens are expansively living in different places on the continent about 70 ,000 years ago, which obviously is not that long before humans are thought to have migrated out 50 ,000 years ago. Yes, that's right. And the question there is, how has the former helped the latter? Is it possible to know?

20:10We think that it helped people to develop systems within their society, within their knowledge base, to cope with adapting to very different environments. We don't know exactly what this would have involved. So it could be developments in how people keep in touch with one another, some sort of cultural, political invention that's not visible in the archaeological record. We don't really know why or what exactly it was, but we do know that this happens during a period of environmental downturn, that they start turning to exploit more habitats probably out of need, and that this pressure delivers an ability to be more flexible, to become specialists in different habitats over time, and that this essentially speaks to our ability to then move beyond Africa.

21:01Obviously, though, a lot of this work is based on modelling and based on archaeological evidence. We know that in this field, a single find can kind of upend things and likewise changes in the climate modelling. There are folk who will read your paper and say, do you know what, this is evidence that this may have happened. But there are a dozen other things as well. What would you say to that? I mean, it's true that we have a lot of sparse data for these time periods, and that's particularly true of fossils, which is why we decided to go for archaeological sites over the last 120 ,000 years, where the climate variables are more robust.

21:33And of course, like my colleagues, they use methods to deal with bias. For example, the further you go back in time, the less sites you're going to find simply because of the attrition right of preservation. You know, we had to account for these things. And your paper's out now, and you've put forward your evidence. What does this not answer? Because this is a debate that will run in the community for a while yet, I suppose. It doesn't tell us how they were doing these things or what specific mechanisms, biological, cultural, were in place that allowed people to respond in this way. Because, you know, there were other downturns in the past that didn't result in this behaviour.

22:11Perhaps between those time periods, there were population increases that create greater pressures. We can't answer that yet. There may be a time when we can, if ancient DNA ever goes back far enough. But if it's a cultural story that we need archaeology for, it's got to be much harder to answer. And if it's something invisible, like a social adaptation, that's got to be very, very difficult to show in any form. But we can see that we know it happened. And we know people left Africa and we are providing a part of the answer. That was Eleanor Sherry from the Max Planck Institute of Geoanthropology in Germany.

22:43For more on that story, check out the show notes for some links. Finally on the show, it's time for the briefing chat, where we discuss a couple of articles that have been highlighted in the Nature Briefing. Ben, what have you been reading this week? Well, I've got a story about breathing, Nick. It's published in the journal Marine Mammal Science, and I read about it on Science Alert. And it's not about humans breathing, it's about humpback whales, and a study looking at ways that they breathe, and something that might be an effort to try and communicate with us. Well, humpback whales are certainly getting a lot of love on the podcast recently.

23:20A couple of weeks ago, you might remember, I talked about how they see, but this is about how they communicate maybe. What have the researchers been looking into here? Yeah, this all comes down to blowing bubbles. Now, humpbacks do that a lot. They use their blowholes and their mouths, and they do it for lots of different reasons. Males do it in breeding grounds. It's like an antagonistic display, for example. it's used to corral prey all sorts of things right and there can be lots of different sorts of bubbles these quite intricate spiral bubble nets they use to catch their food but this work in particular centers on these kind of perfectly circular bubble rings these kind of donut shapes and there's a picture of one of these in the article it's quite something i mean i'm imagining sort of like a smoke ring sort of thing but with bubbles yeah basically that's it right and maybe a couple of metres across, and they break the surface, as bubbles tend to do, in this kind of perfect circle.

24:16And a team, as I say, have been looking at these, and they've been looking at images and recordings of this, taken either below the water by swimmers, or above the water from people on boats or planes, or using drones, that sort of thing. And they've found something maybe unexpected. I mean, you mentioned at the start that this might be a way for them to communicate with us. So are these rings their attempt to be like, hey humans here we are it's a big potential right this is one way that this research has been surmised that it could be an attempt to communicate so specifically they looked at 12 ring producing events if i can describe it like that um which contained 39 of these rings in total some of which were made by more than one whale so like a group of whales and so they've had a look at these and what's going on and 10 of these events happened near a boat or a human swimmer

25:09with whales approaching a boat or swimmers. And the way it's been described, they're showing quite playful behaviour. It's not like they're showing any sort of aggression or antagonistic behaviour. And what's interesting is, in this work, the team have also included data from a separate multi-year study which used drones, hundreds of flights, and this didn't observe any bubble rings at all. So based on this limited data set, it seems like there's potentially an association between humans and these whales doing this particular activity. And if they are indeed trying to communicate with us, what are they trying to say?

25:49That's a great question, Nick. And I went back and rewatched Star Trek 4, The Voyage Home several times to try and figure that out. Didn't help. But I will say that it's not just humpback whales. It seems that lots of other whale species will approach boats and they will blow bubbles maybe not these perfect circles but you know they do show bubble like behavior but these haven't really been studied very much but what's interesting is that bubbles have been interpreted as a way that whales communicate between themselves so double underline maybe but it could be that in some way they're trying to get a message across whatever that may be between people and themselves and i guess we'll watch this space or watch these bubbles i guess to see if researchers can uncover exactly what they're saying.

26:32But that's super interesting. And it's also related to my story this week because it's also about breathing. So I've been reading an article in Nature this week based on a study in Current Biology about how your breath can be used to identify you and potentially as a diagnostic tool. Right. So what? Breaths are like fingerprints? Basically, yes. According to this study, each person's breath is unique to them. so the understanding of breathing is that it's very closely related to the brain the reason that you breathe is to give your brain and other organs oxygen and so therefore you know these things are very closely related and everyone's brain is unique so these researchers thought well if everyone's brain is unique maybe their breathing is as well and so they looked at the breathing of 97 healthy people for 24 hours and then they trained a machine learning algorithm on the different aspects of the breathing that they could detect.

27:28And they showed that most of the time, they could identify specifically who it was just based on their breathing. To me, that's quite unexpected. But of course, I guess, is this just regular relaxed breathing? Because I'm someone who likes to do a lot of sport. Obviously, when I'm swimming, I'm breathing in a different way to when I'm talking to you recording this podcast. So is there one specific sort of breath that each person has? Yeah, there's a specific sort of breath that different people have. So there is basically asymmetry between like how you breathe through one nostril versus the other, how quickly you breathe, all this sort of information can be used.

28:00And it's interesting that you mentioned activity as well because the researchers were less well able to identify people while they were sleeping. So people's sleep breathing was more similar than when they were awake. But the way this research worked is they created a little device attached to the back of your neck and then went into your nostrils and then people just went around their daily activities with this and then they got all the data on how they're breathing. And then they're able to do it to, as I say, train this machine learning algorithm to identify the people and detect certain things about their breathing.

28:32Because the other thing they were interested in was, could this be used as some sort of diagnostic tool? So they gathered data on the participants' BMIs and also their levels of depression and anxiety. And this is a correlation, but they saw that there was a link between the way they breathed and these particular things. So this could be used to identify that someone has depression, for example. Right, because the baseline breathing, this kind of calm, solo breathing, is one fingerprint. But then in a different situation, you can see something else. And that could be used to identify a situation that needs attention.

29:04Yeah, that's the idea, that they could basically see if someone has a condition that maybe their healthcare professional needs to be aware of, or something like that. But also, you could go the other way as well. There is evidence to suggest that how you breathe and controlling your breathing and doing sort of breathing exercises can help with depression and anxiety. So they want to collect further data on the breathing profiles of people to see if there are ways to sort of make the breathing more healthy and therefore make the people themselves healthier. Right, because I covered a story a while back about in mice, if you massively accelerate their hearts, you can induce anxious behaviours.

29:44So people often think about the body and the brain as two separate things, but it seems like there's a body of evidence, if you will, that's coalescing around this idea that really they are part of this one holistic thing. Yeah, and researchers interviewed in this article have said that the most potent tool available to us is our breath. Like, you know, the US military teaches its personnel to control their breath, to manage stress and keep focus in high pressure moments. So the potential is there for this to be used and for more diagnostics to be done in the future. But yeah, more to come from this, I think.

30:14Well, fascinating story there. Nick, thank you for bringing it to the briefing chat. And listeners, for more on those stories and where you can sign up to The Nature Briefing to get more like them delivered directly to your inbox, check out the show notes for some links. And while you're there, you'll also find a link to a survey or you can head to go.nature.com forward slash pod survey 2025. We're looking to find out a little bit more about all of you who listen to the podcast. so if you have a spare minute after finishing this episode then we'll be grateful if you'd follow the link and answer the questions and if you're on Spotify you should be able to answer a quick survey question directly in the Spotify app that's all for now though we'll be back next week with more stories from the world of science until then you can reach out to us on Blue Sky or X or you can send an email to podcast at nature.com I'm Benjamin Thompson and I'm Nick Pertridge Howe thanks for listening Thank you.

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