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S2E05: The World of Giant Touchy Arachnids

This week we imagined what life might be like on a world where the appearance of the night sky changes every year. Get ready for some 8-legged fun!

HOSTED by Dr. Moiya McTier (@GoAstroMo), astrophysicist and folklorist


Dr. Lauren Esposito is an arachnologist and assistant curator at the California Academy of Sciences. Lauren co-founded the conservation non-profit Islands and Seas and the visibility campaign 500 Queer Scientists. The New Science Exhibit about queer and intersectional identities can be found here. You can follow Lauren on twitter at @ArachnologyNerd and instagram at @arachnerds.


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Moiya 0:08

Hello there friends. Welcome to Exolore, the show that helps you imagine other worlds with facts and science. I am your host, Dr. Moiya McTier. I'm an astrophysicist who studied pretty much everything in space from planetary orbits to the radiation leftover from the Big Bang to star formation and black holes and Galaxy evolution. But I am especially interested in the motion of stars and how that affects the habitability of exoplanets, which are planets outside of our solar system. I am also a folklorist who specializes in building and analyzing fictional worlds. And this podcast is my way of sharing those worlds and that knowledge with you. So let's get started.

Moiya 0:52

Thank you so much, Lauren, for being on Exolore. I have been thinking about this world for a very long time. And I have also been thinking for a long time that you're like the perfect person to join me on this episode. So thank you. And in your own words, would you like to tell me and the listeners who you are and what you do?

Lauren 1:12

Sure. I'm Dr. Lauren Esposito, and I'm the curator of arachnology at the California Academy of Sciences. And I guess what that means is that I study arthropods with eight legs, which I think are like the perfect candidate for other planets, to be honest.

Moiya 1:29

Yeah. Why do you think so?

Lauren 1:31

Well, I mean, they were the perfect candidate for ours. Arthropods have been dominating Earth's ecosystems for like 500 million years or so, maybe six? And they've succeeded, exceptionally well. In fact, arthropods on earth today are the greatest concentration of diversity that we see. And so not only have they succeeded in surviving throughout all this time, [but also] during a period of time in which Earth has gone through considerable change, but they've thrived in those circumstances.

Moiya 2:04

Yeah, the fact that I can see spiders in my Manhattan apartment, proves that they can exist in any environment.

Lauren 2:12

Yeah. If you think about anywhere, they're probably there.

Moiya 2:15

So how did you get to studying arthropods, and things with eight legs? No more, no less.

Lauren 2:21

No more, no less. Well, sometimes they have less, but mostly they have eight. I always wish I had some story about how I always knew I wanted to be an entomologist, or an arachnologist and some, like, amazing description of a path that seemed inevitable and when I think back about it, some parts of it, maybe were inevitable, but I mean, I guess I really started in earnest. When I was an undergraduate going to the University of Texas at El Paso, I was like a pretty young college student, because I'd hated High School. And I like hated high school so much that I was either going to drop out or graduate early, and I graduated early and enrolled in the University of Texas at El Paso, nowadays, it's probably more competitive. But at that point in time, it was more like a community college where you could just enroll.

Moiya 2:21

Got it. I love that you're like, "I hate high school, Let me do harder high school".

Lauren 3:15

Well, I actually didn't want to, what I wanted to do when I graduated high school at the age of 16 was get in this old Toyota pickup truck that I had, and like drive around the country and go like camping and national parks. But my mom, who at that point, still had a decision and what I did with my life, because I was 16, was like, "Yeah, I don't think that's a really good idea for my 16 year old daughter to go drive around the country with no job and no money and no security." I mean, you don't get that kind of a scary thing to be like, "yes, 16 year old daughter, like go see the world." So she was like, "I think that you should go to college." And so I enrolled in the local college. I think actually, my mom sort of like enrolled me.

Moiya 3:56

Oh, the power of motherhood.

Lauren 3:57

I know. I mean, my mom is fantastic, so I don't hold it against her. In fact, I guess I have her to think for all of this. I was a biology major, I'd always loved science in school. I loved my biology classes in particular, I think because I had some really great science teachers who encouraged me along that path, but also because both of my parents are biologists. My dad is a veterinarian. My mom went to school for wildlife biology, but mostly worked in my dad's veterinary clinic when I was a kid. And so I grew up with all of it. I'd just been surrounded by it, and I knew I didn't want to be a vet like that much was clear. But what I wanted to do as a biologist, I didn't know and I didn't really have a good sense of what the career options out there were, so I was pre med, because I feel like a lot of biology students are like, "what all do you want to do? I want to make money so I'll be a doctor."

Moiya 4:47

It's a good default. Yeah,

Lauren 4:49

Yeah. And I actually hated being pre med. I didn't really love the classes I was taking like, they were challenging, but not fun. Like all the classes that everybody takes, if you're a science major [are] like Intro Bio and Intro Chemistry and Physics and all those things. They were fine, but I wasn't like, "Ah, this is what I want to do." And it wasn't really until I took entomology class that I was like, "Oh, this is actually really fun!" Because a lot of the class was going out into nature and looking for insects and observing them and collecting them and studying them under microscopes. I love that. And I will say that I still hadn't at that point, but like, "Yes, I want to be an entomologist." I was still pre med and still doing all this stuff. And then the next class I took was one that was mostly motivated because in the course description said that the course was going to Baja, California, Mexico, and spending a week on a beach for Spring Break. And I was like, "yeah, I want to take this class. Of course, that's a no brainer, like Mexico for spring break for school?"

Moiya 5:53

Yeah. Sign me up.

Lauren 5:56

So I did, I took that class. And by the end of that class, I was like, "No, actually, what I really love is field biology and like going out in nature and doing studies," and one of the great things about that class was we had to come up with an idea for an experiment or some sort of study to do out on this beach. And then go and do it during Spring Break. It wasn't just Spring Break on the beach, it was like hard work Spring Break on the beach, but fun.

Moiya 6:21

It was school.

Lauren 6:21

Yeah, it was school and and so I came up with this question that I wanted to answer about whether Fiddler Crabs, you know, this little crabs on the beach that have one big arm?

Moiya 6:31


Lauren 6:32

You've never seen those?

Moiya 6:33

I can imagine it.

Lauren 6:34

Nature channel or something. So they're like little crabs, they live on the intertidal zone of the beach, they dig holes in the sand. And the male crabs have like one major arm and one little tiny minor arm.

Moiya 6:45

Is it the same arm all the time?

Lauren 6:48

That's what I wanted to know, look, great minds think alike.

Moiya 6:51

Look at that.

Lauren 6:51

So I was like, "are they right handed or left handed?" And I like looked through the scientific literature to try to answer this question and couldn't find an answer. So I was like, "that's what my projects gonna be. I'm gonna go to the beach. I'm gonna spend all day on the beach digging up Fiddler Crabs out of the sand and counting how many were right handed and how many were left handed." That's the project I did. The answer was it's like 50-50.

Moiya 7:12


Lauren 7:13

But nobody had ever published any scientific paper on that. And I found that really fascinating that there was like still unknowns as like, relatively simple as that whether Fiddler Crabs were mostly right or left. And that kind of like blew my mind. And since then, I've just made a series of some ways they were missteps, but most, but they all worked out. And in the end, I became an arachnologist.

Moiya 7:36

That's really awesome. Have you ever taken that trip around the country in your truck?

Lauren 7:41

No. But now I get to travel the world, not always on a truck. But usually there's a truck involved.

Moiya 7:47

Good to carry all the equipment.

Lauren 7:49

Yeah, to carry all the equipment and to get to the places that are hard to get to? Because those are the places that still contain a lot of the unknowns.

Moiya 7:56

Where are the coolest places you've been?

Lauren 7:58

Oh, coolest. I mean, that's so hard. Because every place I go to is so cool.

Moiya 8:03

That's a nice diplomatic answer.

Lauren 8:04

No, I mean, it's diplomatic. But I also like I love traveling, I love seeing new places. And so it's not very hard to impress me, I have like a low bar. But I would say one of the most like mind blowingly amazing places I've ever been is this island nation off the coast of West Africa, called Sao Tome and Principe. And it's a small island archipelago of, I think there's five islands, but really just two major islands where people live. And it is like out there in the middle of the ocean. And like the animals that live on these islands are really weird, because they somehow randomly got to these islands that were uninhabited and made their way you know, and were able to survive, and it's a really cool, very special place.

Moiya 8:47

That's awesome. Okay, so to change tracks a little bit to get into the fictional world theme of the show. I always ask my guests what fictional worlds you've been inhabiting lately, whether that's books, movies, video games, whatever. So where have you been in your mind?

Lauren 9:06

Ah, man, that's such a good question. I mean, I read a lot of books and like mostly the sorts of books that I read our science fiction worldbuilding kind of books that are like fast reads. I like youth sort of novels.

Moiya 9:21

Like YA stuff?

Lauren 9:22

Yeah, like young adult because I really like book[s] that I can [read],and I'm done with it in like six hours and ready to move on to the next one.

Moiya 9:29

Oh, you don't get that like post-book ennui where you can't go into another world for a while?

Lauren 9:34

I don't, I can just read them back to back but oftentimes, [I] have phases of reading so I'll be on a field trip and have budget downtime to read. And I'll like power through like three books and just be like completely absorbed in them. Maybe it's like a rainy afternoon on a tropical island, and I can't go out and work so I just want to read a whole book. And then I don't wanna have to remember where I left off because that's my biggest problem, once I stop reading [it's] like I can't remember what happened. And then after we read the whole book, and it's very frustrating.

Moiya 10:06

So short books. What have you read lately? Do you remember any titles?

Lauren 10:12

Oh, man, I'm reading a book right now. And I can't even remember what it's called.

Moiya 10:15

What's it about?

Lauren 10:16

It's about a world where there's a wall, and on one side of the wall magic happens. And on the other side of the wall is just like normal humans. I wish I was more prepared, but it's great. I love the book.

Moiya 10:28

That's okay, I sprung this question on you.

Lauren 10:31

But it's really cool because like, on both sides, people are sort of aware of the other side, but there's not really like a lot of crossover.

Moiya 10:39


Lauren 10:40

And on the side where magic happens, like, that's very normal, and matter-of-fact, and on the other side, like people are like, "What? No, that can't really be real."

Moiya 10:48

Which side would you want to live on?

Lauren 10:49

Well, the magic side seems kind of terrifying because there's a lot of people rising up from the dead.

Moiya 10:55

Don't like that.

Lauren 10:56

Yeah, that sounds frightening. I mean, I feel like I'd like to live kinda in the almost border zone on the normal side. Because then like, once in a while, something really cool magic[wise] happens, but like, not usually something devastating, like a whole army of dead rising.

Moiya 11:11

Yes. Good to avoid that. Keep a wall between you and the undead army.

Lauren 11:16

Yes, exactly.

Moiya 11:17

At least one wall.

Lauren 11:18


Moiya 11:19

Cool. Well, are you ready to build our own fictional world?

Lauren 11:23

I think so.

Moiya 11:23

Yes. I'm really excited about this one.

Lauren 11:25

I was kind of nervous to be honest. I feel like most of the time, I just get asked facts and this time, I get to be creative.

Moiya 11:32


Lauren 11:32

It made me feel nervous.

Moiya 11:34

Oh, I still get nervous, if that helps you. But hopefully, by the end of this, you'll have had a great time.

Lauren 11:40

No, I'm excited.

Moiya 11:41

Okay, good. So the world we're building today is one where there's an ever changing night sky. So from the time that it takes the planet, this world to get from like the same part in its orbit, make a whole orbit over a year and then get back to the same point, the constellations in the sky have changed. That also happens from season to season, the constellations are changing, but that happens here on Earth, too. So the important thing is that the constellations are changing every year in this pretty unpredictable way. And the way that you can get that to happen is if your planet is in a dense stellar environment, like a globular cluster, which are these clusters of stars, anywhere between 10 and a few 100 light years across, and they can have like 10s or 1000s of stars in them. For reference, the part of the galaxy that we're in there are maybe like a couple of stars within 10 light years. So it's much denser than our part of the galaxy, there's more radiation there because stars are giving off radiation. So high amounts of X rays, UV rays, and Gamma rays. And a lot of these stars in the globular clusters are going to be much older than our Sun. So our Sun is about four and a half billion years old. Most of these globular clusters we think are probably remnants of old galaxies that have merged with the Milky Way. So they have older stars. So let's imagine that the average age of a star in this globular cluster is about twice as old as our Sun. So these stars are 10 billion years old, the planets themselves are going to be really old. So I'm thinking like, maybe time for lots of mass extinction events in the past on this world? We can play with that as we will, but but that's what we're working with. So do you have any first reactions to any of that?

Lauren 13:21

I mean, I think [my] first reaction and of course, my thoughts are always biased towards arthropods, which [works because] arthropods are perfect for this because they like would be able to effectively deal with high levels of radiation, high levels of UV and in particular because they have exoskeletons that help them to deal with that; they have armor on the outside. My second thought is like when you talk about an old world, one thing that comes to mind for me is really sort of decomposed rock, so like imagine that the world is probably kind of like cooled down a little bit where there's not active magnaflow if there ever was and that the rock is like cooled and had lots of times to erode, and so it's like this kind of crumbly landscape that's what pops into my brain so those are my initial thoughts.

Moiya 14:09

I love that already. The exoskeleton is that made of the same type of stuff is our skeleton like all the calcium and whatever else is in bones?

Lauren 14:19

Yeah, so it's more like hair or fingernails, it's made out of a material called chitin. So not the same as our skeleton, it also forms simultaneously around the entire organism. So take the example of a spider, spiders when they molt their exoskeleton, which they have to do in order to grow because it constrains their size, they molted and their whole entire body all their skeleton comes off all at once simultaneously, but also so does their entire digestive system and the reproductive organs and like everything else is just all comes off. So they start over again, periodically. So if it were to get damaged because of high radiation, or UV, then like suddenly they have like a whole new digestive system and like new coverings on their lungs and everything, all of it.

Moiya 15:07

Yeah, you're right. They are perfect for this environment. So besides the exoskeletons, what other physical or biological traits do we think would do really well in this environment?

Lauren 15:17

I mean, I guess when you say the stars are much older, they're probably giving off considerably less light. Is that true or not true?

Moiya 15:25

Less visible light, but they're still giving off light, and other parts of the electromagnetic spectrum. Yeah.

Lauren 15:31

So I mean, I guess like thinking too, about, like, how much gas would be present in the atmosphere, I'm thinking about maybe things that are able to deal with relatively low levels of whatever gas they need, like, presumably oxygen, because that's the way that we interpret most living organisms on earth is the need for oxygen or carbon dioxide. So probably like lower than we're used to here on Earth, levels of those gases

Moiya 15:55

Oh, especially like you said earlier, if there's not much geological activity happening inside, like, if the planet itself is kind of cold and dead in a way, then there won't be the carbon cycle that can get a lot of the carbon dioxide out of the air. So I'm thinking higher rates of that.

Lauren 16:12

That's absolutely true. So it may be that the autotrophs or things that are like using raw energy from the sun to create other forms of energy have to be using some alternative, like mechanism other than the way that plants do here on Earth. Like, I'm thinking more like deep sea events.

Moiya 16:30

Like a chemosynthesis.

Lauren 16:32

Yeah, some kind of chemosynthesis, and those autotrophs, I feel like they're gonna be the cornerstone of whatever the the food web is. But they don't actually matter that much. Because they'll always be something that's really successful at taking raw energy and converting it. That's going to be like the basis of any ecosystem anywhere, no matter what the makeup of that planet is.

Moiya 16:53

That's a good point. So maybe let's focus our conversation on what we think would be at the top of that food chain.

Lauren 17:00

Right, which is why I'm here. I'm here to talk about the predators.

Moiya 17:03

Yes, you are.

Lauren 17:04

Things that come to mind for me right away that I think make arachnids really probable and like arachnids for the record have been featured in Sci-Fi worlds as being like the top thing.

Moiya 17:15

Oh, okay. They're beating out crustaceans?

Lauren 17:19

Although I feel like sometimes the representation to be honest, is like sort of a hybrid between crustacean and arachnid, which is fine, fine by me, they do share a lot of similarities. But arachnids, like scorpions have the lowest metabolic rate of any animal on earth.

Moiya 17:33

Is that good?

Lauren 17:35

That's great, because then they can like survive. If there's like periods where I don't know like there's decreased solar activity or something, they can survive those hurdles [with] decreased metabolisms so they don't need as much oxygen and they don't need as much food and whatever water kind of liquid things they would use.

Moiya 17:54

That's really nice, but I imagine they're also probably not very active during that time. Is it a hibernation almost?

Lauren 18:00

It's not really hibernation, they're still fully active. They just have really low metabolisms. Like, they don't need a lot to get by.

Moiya 18:06

Oh, wait, that's really cool. They don't need a lot of resources from outside, but it doesn't necessarily affect their day to day behavior as much?

Lauren 18:14

No, yeah. Like, they may be like a little less active than normal, but they'll probably still have like, more or less normal activity levels.

Moiya 18:22

That's really great. That'd be useful here. So what do we think they look like? What are you imagining in your head?

Lauren 18:29

Well, I think about the history of arthropods on earth; and historically, they were really big, but they were really big because I was really high oxygen concentration levels on earth. And so in this scenario, if there's lower oxygen concentration levels, and they probably are really small, rather than really big, which is kind of a bummer, because I would like them to be like, gigantic.

Moiya 18:50

Why does the amount of oxygen effect size?

Lauren 18:53

Because they passively respire. So instead of having lungs that breathe in and out, they have more like gills structures? Actually, they are internalized gills that oxygen just diffuses over. And so the concentration of oxygen in the air limits their size, because they're limited by the rate that they can absorb oxygen and get it in all their tissues.

Moiya 19:13

Got it. So if there are some of these creatures, these life forms that are near sources of a lot of oxygen, then they can get bigger?

Lauren 19:22


Moiya 19:23

Is it like on the individual scale? Or does it happen more over time?

Lauren 19:28

It happens more over time, which may be reflected on the individual scale and that like the larger ones, are able to have more offspring. but are only able to survive if they have access to higher oxygen concentrations. So like over time, larger sizes get selected for instead of against.

Moiya 19:45

Got it. So I would love the idea of the species, being able to tell where someone else is from based on how big they are. Like if there are families that are from different parts of this planet and some parts are like maybe in a forest where there's going to be more oxygen. They can get bigger.

Lauren 20:01

Well, here's the thought, what if in this world because it's a crumbly world, and it's had lots of time for erosion, there's like big cave systems underground. And those cave systems could like harbor greater levels of oxygen from like back in time when there was more oxygen on that planet. And so cities are built around caves that have higher oxygen levels. And so they're also kind of like restricted to those caves because there's a urban growth constraint where the cities can't grow any larger because they have to stay in their own cave system. And the next city is like the next cave system over.

Moiya 20:34

I love that a lot. I really do. Do we think given this planet's long history that the - should I call them arthropods?

Lauren 20:44

Call them call them arachnids.

Moiya 20:45

Arachnids. Okay. Do we think these arachnids have always been the most powerful species on this world?

Lauren 20:55

If we take a page from the book of Earth, we can say that they had their moment as like the top predators of the ocean. And then when everything moved on to land, in this case, eventually the oceans in this world dried up,maybe? It's an old world, there's not so many oceans. Then during their time on land, they would have gotten smaller. Because also the other thing about the ocean is that it removes like gravity limits. So body size can be larger because there's not as much gravitational restrictions about how to move and how big you can be.

Moiya 21:27

There's buoyancy in the water.

Lauren 21:29

But then they came on land, and they got smaller on land and oxygen levels went down. And eventually they found the caves, which is the thing that actually happens, like we know that that happens on Earth, like caves are oftentimes rifugio during a global change events. So like things find their way into caves. Maybe there's like a glacier covering up the forest that they used to live in. And then when that glacier recedes again, things come back out of caves and reoccupy the forest as it grows back. So if they found their way into caves as like, the oceans were drying up, and they were looking for, like moisture, and oxygen rich pockets, everything else may have died off. And since that time, they've returned back to the rightful place as top predators.

Moiya 22:11

Yeah, I like that a lot.

Lauren 22:14

But they had to live in fear for a while, like that intervening time between ocean and cave. They were you know, they weren't [at] the top.

Moiya 22:20

It'll build character for the species. How long do we want them to live? Do we want them to have long or short lifespans? Do you think?

Lauren 22:29

I feel like something intermediate, like a 25-50 year lifespan.

Moiya 22:34


Lauren 22:35

Is that long?

Moiya 22:36

Is that long for a scorpion here on Earth?

Lauren 22:38

A Scorpion on Earth can live somewhere between 7-25 years.

Moiya 22:44

Okay. One of the advantages, I think of having a long lifespan is that an individual person can contribute more before they die. So I think that that makes it easier for the species as a whole to advance more quickly. So I see that as a proxy for how quickly can this species advance. So if we're thinking intermediate lifespans, then intermediate rate of advancement.

Lauren 23:09

True, but I wonder to what extent [how quickly] you become an adult factors into that. If you have an intermediate lifespan, but reach maturity at human rates, you only live 50 years, [hence] you're not mature until [about] 18. But if you reach adulthood by 3, then that's a whole different scenario like that maybe makes your life comparatively longer.

Moiya 23:39

I hadn't even considered that, that's a really great point. So reaching maturity around 3, is that typical?

Lauren 23:44

Yeah, I would say that somewhere between 1-3 for scorpions, that's about right for spiders, like within a few months, in many cases, and then others, like sort of 1-3 year timespan.

Moiya 23:56

How related are spiders and scorpions?

Lauren 23:59

They're not each other's closest relative, but they're part of a group that is all each other's closest relatives. So there [are] two other things that are missing from [this] conversation, and they're groups of arachnids that nobody really has ever heard of. So for all intents and purposes, they're basically each other's closest living relative.

Moiya 24:17

Okay, what's left?

Lauren 24:19

The other two are a group called Whip Spiders or Amblypygis. They kind of look like a crab. They actually are one of the most cave adapted groups. They have six pairs of walking legs and two legs that are like these long, crazy antennae that they use to like feel around. Most spiders and scorpions have venom, but these guys don't have venom. And then the other group is Pseudoscorpions, which look kind of like a scorpion, but doesn't have a tail and it's really tiny.