Why Do Spiders Have Eight Legs?
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This is But Why, a podcast for curious kids produced at Vermont Public Radio. You send us the questions and we find the answers. I'm Jane Lindholm and I host the show. Today we're covering something that almost everyone has at least some experience with. Spiders. Now, a lot of people have the wrong idea about spiders. They think spiders are creepy or scary or out to bite you just for the heck of it.

But not you, you curious but wild listeners. You have sent us lots of questions about spiders, so it's clear you are eager to learn more about these remarkable creatures. Today we're bringing back an episode we did in 2018 all about spiders, because we think some of you may have missed it the first time around. And even if you didn't, it's worth another listen.

But first, we wanted to let you know about something that is new. We have brand new coloring pages to pair with some of our episodes, including this one. There's a beautiful illustration of different kinds of spiders by Hillary Ann Love Glass to go along with this episode. You can have an adult help you print it out and then color while you listen. All of our coloring pages are at butwhykids.org.

Back to spiders. Here to help answer your questions is Katherine Scott. She's an arachnologist. What's an arachnologist? Well, it's someone who studies arachnids. But what's an arachnid? An arachnid is an animal that has eight legs.

And that's the main defining feature. Spiders are arachnids. So all spiders are arachnids, but not all arachnids are spiders. There are several other kinds of animals that also have eight legs that are closely related to spiders, but aren't spiders. There are other arachnids like scorpions, like mites and ticks.

And there's a bunch of other ones as well. So most of our questions, well, all of them really, are about spiders, which are probably the most famous arachnid. Why do you study spiders?

I study spiders because their behavior is fascinating. I also think they're really beautiful and everything about them is interesting. But I'm particularly interested in their behavior and how they communicate with one another. Basically, what I study is how spiders talk to each other, but they don't talk to each other like we do. They use chemicals called pheromones, and they also use vibrations and other ways of talking to each other.

I always think of spiders because I guess that's how I see them as solitary animals. They're by themselves. They do, though, communicate to one another? You're right that most spiders are solitary and they spend most of their lives alone. But all spiders reproduce sexually so that they at least have to get together when they want to make friends.

So in order for a male spider to find a female spider, they have to communicate somehow. He has to figure out where the female is. And so that's where these chemicals called pheromones come in. The female basically has to produce...

It's like a perfume that she produces that the male can smell from some distance away in order to find her. Not all spiders rely only on chemicals to find each other. Some spiders have good vision and they can just see each other because they're wandering around all the time. But your typical solitary web-building spiders, you know, the female is sitting on her web and she basically stays there her whole life. So in order to mate...

and reproduce, a male spider has to come to her. And so she has to communicate where she is in order for him to find her. So that perfume says, hey, I'm over here. I'm ready to make babies. Exactly. All of our questions about spiders are really interesting, but let's start with the first one from Sasha, because this is a fundamental question, Catherine. I'm seven years old. I live in New York City, and

And my question is, why do spiders have eight legs and eight eyes? Can't they just handle four legs and two eyes like most predators, or two legs and two eyes like a few other predators? I really like this question. It's a little bit hard to answer, but I'm going to try. So having eight legs gives spiders some advantages.

For example, if a predator grabs them by their leg, the spider can actually drop their leg and run away and survive, and then they can get around just fine with only seven legs or even fewer. So I've actually found some spiders running around with only four legs because they have dropped the other ones earlier.

when a predator was trying to attack them, they bit the leg, and then the spider's able to go like, oh, I'm just gonna leave that leg behind and run away to survive. And the thing about spiders having eight eyes, it's true that most spiders have eight eyes, but not all of them do. Spiders can actually have eight eyes, six,

six eyes, four eyes, only two eyes like we do, or even no eyes at all. Wow. Yeah, so some spiders live in caves and they spend their entire lives in the dark, so they don't need eyes, so they don't bother with them. While we're talking about eyes, let's listen to this question from a three-year-old in California. My name is Toga. My question is, how do spiders see? The number of eyes and how well spiders see depends on what kind of spider you're talking about.

Hunting spiders, like jumping spiders and wolf spiders, have one pair of really large eyes that allows them to see prey and each other really well. But many spiders that live in webs can't really see images with their eyes like we can. They can only detect things like light and dark and movement. And so they rely much more on their senses of touch, smell, and hearing than on eyesight. Does having eight eyes...

the ones who do have eight eyes, does that give them an ability to either see in more directions than we can see or see differently than humans see?

Yeah. So for jumping spiders, for instance, they have eight eyes and they're spaced all around their head. So that means that they have almost 360 degree, like if we had eyes on the back of our heads, we'd be able to see behind us as well as in front of us. So having eight eyes spaced out definitely does give spiders some advantages. Some human parents claim that they have eyes in the back of their head and they can see what's happening when their kids are behind them. But spiders really do in some cases. Yes.

Some spiders actually do have eyes on the back of their heads. The other thing that everybody knows about spiders is that they build webs. But I think maybe not all spiders, but let's listen to some of our web questions. My name is Nico. I'm five years old. My name is Jolie, and I am eight years old. My name is Malia, and I'm eight years old. We all live in Los Angeles, California.

And our question today is, how do spiders make their way?

First, let's talk about how spiders make silk. So they have storage facilities called silk glands in their abdomens.

The abdomen is the back end of the spider. And they store the building blocks of silk in liquid form in these silk glands. So when the spider wants to make silk, the liquid moves out of the gland through a valve that's controlled by the spider's muscles. And then it's released out of tiny openings called spigots on the spider's spinnerets, which are located at the tip of their abdomen.

So the liquid silk then turns solid as it leaves the spider's spinnerets. It's kind of like Silly String. Is that right? I mean, if anybody's ever played with Silly String, it's kind of like a liquid or, you know, not solid inside the can, but as soon as it comes out, it turns into a solid. That's what spider silk is like? Pretty much. Yeah. Yeah. They've got this can of liquid silk.

inside of their body, essentially, and then a valve. And yeah, when they want to make silk, it's like pressing the button on your silly string can, and this, it becomes solid as it leaves the can. That's a great analogy. Exactly how the process of turning that liquid silk into solid silk is still a bit of a mystery.

Scientists have actually been trying to build silk-making machines for a long time, and although we do know the recipe for the liquid silk, so far only spiders are actually able to turn it into solid silk. So they're able to make this really strong, solid, elastic thread that they use to build their webs. It's a really cool material, and humans can't replicate it yet. Yeah.

But I can walk through a spider web and break it. I always hear that spider webs are so strong, and yet I walk through them no problem. So how are they supposed to be strong?

Yeah, so you might have heard that spider webs are stronger than steel. Silk threads that spiders make are sort of strong for their diameter. And they're also, it's not just that they're strong, like, yes, you can break them. But if you put your finger into an orb web, for instance, it's going to resist, right? And it's kind of like an elastic band. Like, you'll, it'll take a while before it actually breaks. Right.

So it's strong and elastic. And so it has properties that are really useful for humans. And depending on how you kind of...

combine the silk and make things out of it. There are some people who are working on trying to make like bulletproof vests from Black Widow silk. And it's not like one strand of Black Widow silk isn't going to stop a bullet. But a lot of these silk strands together can be really, really strong and really flexible. The other thing that people know about spider webs, because it happens when we get caught in them, is how sticky they are. Hi, my name is Eli.

I live in Bozeman, Montana, and I have a question. How do spiders not get stuck in their webs? Hi, my name is Nora. I am five. I live in Fort Worth, Texas. My question is, how do spiders not get stuck in their own spiderweb?

My name is Max. I am seven years old. I live in Mesa, Arizona. My question is, how do spiders not stick to their own webs? How do spiders not get stuck to their own webs? So first of all, there are lots of different kinds of spider webs, and not all of them are sticky. But usually people are thinking about the orb webs that spiders in your garden build that have this sticky spiral that is used to capture flying insects.

The spiders that build those webs have to move around on their web, right? So while they're walking around on the web, they can just avoid the sticky lines because not every single strand of the silk in that web is sticky. But they do have to touch the silk with their legs while they're building the web and they manage not to get stuck to it.

it. So the way that they avoid getting stuck to their own silk is that their feet, which scientists call tarsi, are covered with tiny hairs that decrease the amount of surface area that makes contact with the silk. And they also have a kind of non-stick chemical coating on their feet that helps the bits that do touch the silk not get stuck to it. And they're also just really careful about where they put their feet.

Here's something cool that spiders, some spiders at least, can do, and they can walk on walls. I mean, we all know Spider-Man can walk on walls, but he got that skill from somewhere, and it's the spider. So here are a couple of questions about that. My name is Elias. I live in Bozeman, Montana, and I am five years old. My question is this.

How do spiders stay on the walls and ceilings and not fall off? I'm five years old and my name is Memphis and I live in Edmonton, Canada and I want to learn about how do spiders climb on walls.

Before, when we were talking about how spiders avoid get stuck into their silk, it was all about having hairs on their feet, right? So how spiders are able to walk on walls and ceilings is also about increasing surface area with hairy feet. So some spiders, the ones that don't build webs, have something called claw tufts on their feet. So these are basically super hairy pads that help them stick to flat, smooth surfaces like walls. So...

The spider's foot is covered with this dense tuft of hairs, and then each of those individual hairs is covered in hundreds of thousands more, even tinier hairs. So this means that the spider has a huge number of tiny points of contact with the wall. And the way that they stick to the wall is through something called van der Waals forces.

Vanderwall's forces work when two molecules are really close to each other and are attracted to each other. So these are really weak forces, but a lot of them together can be really strong. So the attraction between millions of tiny hairs on the spider's foot and the wall allow the spider to stick, but it's also not so sticky that they can't walk around. So it's basically kind of like the spider having post-it notes on their feet that are sticky enough to stay on the wall, but easy to peel off.

Imagine having to walk around your house being really careful about where you put your feet because you might get stuck in the middle of your bedroom or something. But also being able to walk up the walls of your room when you want to. I would like that skill. Coming up, how do spiders choose where to make their sticky webs? And how can you help the adults in your life, or maybe you yourself, be less afraid of spiders?

This is But Why. I'm Jane Lindholm, and today we're answering your questions about spiders with arachnologist Katherine Scott. Remember, arachnids are animals with eight legs. They're not insects. Arachnids have their own special classification in the animal kingdom, and they include ticks and scorpions, and my favorite, the pseudoscorpion.

Arachnids are arthropods. That means they're animals that don't have bones like you and I do to keep our bodies in the right shape and help us move. Arthropods have an exoskeleton, a shell, that serves the same purpose. It gives their body their shape and keeps all their organs inside.

Today we are concentrating specifically on spiders. We were just talking about the webs that many spiders build. But how do they know where to build them? Hello, my name is Johanna and I am four and three quarters and I live in Minnesota. And my question is, how do spiders choose a place to make their web?

Basically, they want to choose somewhere that's safe and where there's lots of food to eat. So some spiders use their senses of smell and taste to figure out if there is a good source of food around when they're choosing a website. You might find spiders in your house. Some spiders might have put up a web in a window or near a light.

inside or outside your house. And the reason for that is that they are detecting that it's a good place to find prey. So you might see, especially outside lights, might often have a lot of spider webs around them. Insects like moths are attracted to bright lights at night. So the spiders are able to detect that, oh, there's a light here. It's going to be a really great place to capture a lot of moths and other flying insects. And so they choose that place to set up their web.

Hello, my name is Roy and I'm seven years old and I'm from Barbersville, Virginia. And my question is, what's the difference between a spider web and a cobweb? And what is a spider web made of and what is a cobweb made of? So that's an interesting question. The answer probably depends on who you ask.

Someone who has messy old spider webs in their house or their basement might call them cobwebs. But arachnologists call the messy looking webs of spiders like black widows and cellar spiders cobwebs. Whereas the beautiful spiral webs of garden spiders are called orbwebs. And so there are actually a whole bunch of different kinds of spider webs that are made by different spiders themselves.

different families and species. So some spider webs are triangle shaped, some are dome or bowl shaped, some are funnel shaped, and some are more like flat sheets. So cobweb is actually a term that's used to describe a particular type of messy web that's not organized like orb webs are.

Katherine, do all spiders build webs? No. It depends on the lifestyle of the spider and the type of hunter that they are. So some spiders that are wandering hunters don't ever build a web.

for instance, jumping spiders and wolf spiders, two of the spiders that have really good vision and are visual hunters, kind of like cats that pounce on their prey, they don't build webs. But a lot of spider species do build webs, like orb weavers that build webs to capture flying insects,

or other spiders that build webs closer to the ground to capture crawling insects. So it depends on what kind of spider you're talking about. And actually, there are more than 45,000 different kinds of spiders in the world that scientists have names for. There are actually more that we haven't named yet. So there's a whole bunch of different kinds of spiders. And depending on the family that they're in, they may or may not build a web that they use to capture insects. Wow.

Wow, more than 45,000 different kinds of spiders. Worldwide, every year, spiders eat somewhere between 400 and 800 million tons of insects, which is a lot. Yeah. That is a lot. While we're talking about eating, let's get to our eating questions. My name is George, and...

And I want to know. Three years old. And I'm three years old. From Michigan. From Michigan. My question is, how spiders eat? Hello, my name is Elliot. I live in Seattle and I'm four years old. My question is, how do black widows eat their food? I'm Eric.

And I'm five years old. I live in Wisconsin. And my question is, how do spiders eat flies? Spiders have a really cool and kind of gross way of eating their food. They actually start digesting it outside of their body. First, they either paralyze their prey with venom or wrap it up in silk to subdue it, or they do both.

Then the spider regurgitates or spits up digestive fluid either onto or into the food item. So what happens next depends on whether or not the spider has strong jaws. Some spiders chew their food before they eat it, just like we do, to help break it down before they swallow it and finish the rest of the digestion process in their guts.

But other spiders, like black widows, pump digestive fluid through a tiny hole in the exoskeleton of the insect they've captured and wait for the insides of the insect to start being digested. And then once the insides are soft enough, the spider sucks them up, just like drinking a milkshake through a straw. So with the black widow, it's actually kind of waiting for that inside of the insect just to turn into a slushie? Yes. Yeah. Yeah.

So once the black widow is finished eating its prey, you'll be left with the exoskeleton of that insect. And it'll look almost identical to the way it looked when it was alive, but it'll just be a shell and all of the insides will have been sucked out by the spiders. That's both gross and cool. Yeah, yeah.

Other spiders, like wolf spiders, for instance, that have bigger jaws, they'll munch on the insect while they're eating it and chew it. And so you won't necessarily be able to tell what they've eaten afterwards because it'll be...

There'll be lots of bits of the exoskeleton left behind because the spiders can't digest those. But with black widows and some other spiders that have puny little jaws and can't really chew their food, yeah, you're left with just this empty shell of an insect. Do all spiders eat insects? Yes. All spiders eat insects, but insects aren't the only thing that spiders eat.

So the majority of spiders eat mainly insects, but they also eat other arthropods, including other spiders. And some spiders can actually eat vertebrates, so animals with backbones like us. So some spiders called fishing spiders prey on small fish and tadpoles. They actually live on the edges of lakes and ponds and can dive under the water to capture fish.

And then some other spiders, like black widows, for instance, can prey on small lizards and small snakes or even small rodents. And spiders like the really big tarantulas that live in South America can also eat larger vertebrates like birds and frogs. Whoa.

I didn't realize that some spiders could eat fish. Yeah. And birds and frogs and rodents. Yeah. Spiders are predators. They're carnivores that eat other animals. But some of them do also eat plant-based food. So some spiders feed on nectar produced by flowers.

Orb web spiders, like the ones you see in your garden, pollen sometimes gets stuck on their sticky silk. And these spiders take down their webs every night or every couple of nights. And they actually eat up the silk and recycle it.

And if there's pollen on the silk, they also eat that pollen. And that's nutritious as well. You know, all of this is very interesting. But what if you're afraid of spiders? A lot of people are. And it's true that some spiders are venomous. Venom is a chemical, or really a combination of chemicals, that an animal like some spiders and some snakes can use to attack their prey or to defend themselves.

Poison is actually kind of different from venom, and spiders aren't generally poisonous. By that I mean that the spider itself isn't harmful. If you licked a spider, which, by the way, I do not recommend, it wouldn't hurt you to lick it. And in some cultures, spiders are a delicacy. Some cultures eat, for example, tarantulas. But if a venomous spider bit you with that combination of chemicals, it could make you very sick or in some cases actually kill you.

So you do need to be cautious around spiders and have an adult help you figure out which kinds of spiders are dangerous and which ones are not. But Katherine Scott says you really shouldn't be afraid of spiders. Spider bites are extremely rare.

spiders eat insects. They don't eat people. So some arthropods like mosquitoes and ticks and bedbugs feed on blood. Spiders don't do that. They don't eat us, so they have no reason to bite us. There are some spiders that are capable of causing harm to humans if they bite us, and those include spiders like the black widow.

There's really no reason to be afraid of spiders. Spiders don't want to bite you. And if you leave them alone, they're going to leave you alone and they don't pose a threat.

So basically, you should be cautious of spiders the same way you are of any wild animal, but you don't need to be afraid of them and they're not coming for you. They're not trying to bite people. Absolutely. Yeah. Spiders are not interested in biting you. And, you know, if you grab them with your bare hands or crushing them, they're going to bite defensively because they're scared. They have no other option. Biting is kind of a last resort. But spider venom is for spiders.

It's for eating insects and other arthropods. It's not for hurting people. Last question here from Izzy. I come from Durham, North Carolina, and I'm six and a half years old. My question is, why are daddy longlegs called daddy longlegs when they have to have a female to produce their babies? This is a great question that I don't have a really good answer for. The name doesn't make a lot of sense.

People use daddy longlegs to describe three different kinds of animals. The first one is another arachnid called Apiliones. The common name is Harvestman, which also doesn't make much sense because they are not all male, so I prefer to call them harvesters. And then even some flies called craneflies are called daddy longlegs by some people. But I assume, because this is about spiders, that the question is about why some spiders are called daddy longlegs. So...

The spiders that people call daddy long legs are also known as cellar spiders, which is the name I like to use for them. So Izzy is right. They're both male and female cellar spiders, but,

But for some reason, we don't call the females mama long legs. So this name really doesn't make much sense. Nobody seems to know where the daddy part of the name comes from. So I really don't have a good answer for the question. But the long legs part does make sense because these spiders have extremely long, skinny legs. What's the benefit to them of having such long, skinny legs? Having

long skinny legs can be advantageous for cellar spiders because it allows them to stay really far away from their prey when they're trying to capture it. So cellar spiders can actually eat spiders that are much bigger than them. Cellar spiders are a web-building spider.

They spend most of their life on their own messy cobweb, but they also can leave their web and wander around and sometimes will even enter the webs of other spiders and capture that spider. And so their method of prey capture involves wrapping the prey item with a whole bunch of silk, but because they have such long legs and they use their legs to

and they use their legs to pull silk out of their spinnerets and sort of throw it at the insect, they can stay really far away from the insect because their legs are so long, and that helps them avoid getting injured by an insect or other spider that's trying to fight back.

Catherine says spiders are really cool. And if you don't like them, maybe you just need to spend a little more time with them. Spiders are beautiful. I think if you spend some time watching spiders, you'll find that a lot of them are really beautiful. My favorite thing about spiders is that they have really cool behavior. So if you watch them, you'll find that they're really cool.

You can learn a lot about them. Their prey capture behavior is really interesting. If you find a spider web in or around your house and you can find a small ant or a fly or something and put it on the spider web, you might be able to see how the spider captures its food. And that can be really, really cool.

I also think it's cool that spiders have really sophisticated communication systems. So they are able to talk to each other using vibrations, sounds, chemicals, smells. And so they have a lot to say, and they're having conversations that we can't hear, but they have rich lives, and that's really cool, I think. That was arachnologist Catherine Scott.

When we talked with her, she was studying black widow spiders at the University of Toronto. Now she studies two other arachnids, mites and ticks, at Acadia University.

Thanks so much to Katherine for educating us on spiders today. If you wind up doing some spider studying of your own, let us know how it goes. We'd love to know what you learned to appreciate about the spiders in your home or yard. And don't forget, we have new coloring pages for many of our episodes available on our website for your adult to print out so you can color as you listen or afterwards, including some cool spiders you can color. You'll find them all at butwhykids.org.

If there's something you want to know more about, send us a question. We love hearing from you about all topics big and small. It's easy to send a question. You just have an adult record you asking it. You can do that on a smartphone using a built-in memo function. Be sure to include your name, your town, and how old you are. Then send the file to questions at butwhykids.org.

But Why is produced by Melody Beaudet and me, Jane Lindholm, at Vermont Public Radio. Our theme music is by Luke Reynolds. We'll be back in two weeks. Until then, stay curious. From PR.