This episode is sponsored by Endel, an app that creates personalized soundscapes  to help you focus, relax, and sleep.

The first 100 people to click our description  link will get a one week free trial. [♪ INTRO] Spiders are generally solitary critters. Of around 50,000 species of spider, something like 99.96% prefer to  live by themselves most of the time.

But about 20 species have evolved to be social. Some of their colonies grow to cover entire trees and host tens of thousands of individuals. And these unusual populations are a  rich natural experiment in social living that scientists have been investigating for years.

There’s a saying attributed to Isaac  Asimov that goes something like “the most exciting phrase in science  isn’t ‘Eureka’, but ‘Oh, that’s weird’.” And these spiders are so weird. Exploring how they live may  not only help us understand these social species better, but it  could also have practical applications, including teaching us how to make better robots. So, real quick, let’s define what  it means for a spider to be social.

Because while many spiders  spend their lives on their own, every species spends a little bit  of time being quote-unquote social. We wouldn’t have baby spiders if they didn’t. And there are some species that spend  a good amount of time living in groups, but they still kind of do their own thing.

But truly social spiders don’t just live in the  same place, they actually seem to work together. Multiple families may live together  for generations, often building massive communal nests, hunting,  and raising young together. Even though the species that do this  are extremely rare in the grand scheme of things, they appear on every  continent other than Antarctica, and they may have evolved independently  at least 15 different times.

So, we can’t just chalk up their  existence to a rare mutation that randomly happened once and turned out to be successful. Certain evolutionary pressures have pushed spiders to evolve social behavior multiple times. And scientists have a few ideas why that might be.

One of the major advantages  of social living is that, with larger webs, spiders can  catch and eat larger prey. That way, they’re not competing for the same  prey as other spiders that are hunting solo. Also, because they’re all sharing the same  nest, any given individual likely spends less energy on building and repairing  the nest compared to a solitary spider.

Another idea is that living together with  many other spiders could be especially helpful in areas with a lot of predators or  a lot of rain, which can damage spiderwebs. These are just hypotheses for now,  but they help highlight why this rare evolutionary step may  have happened various times. Whatever their reason for sticking  together, social spiders can reveal some interesting things about  life as a social species.

For instance, scientists  have long been interested in how individual personalities  shape collective behavior. Because, yes, spiders and other animals  can have different personalities. It might be hard to notice if you’re  just looking at one spider at a time, but scientists can measure certain behaviors  that reflect different personality traits.

Like how quickly one spider  attacks prey compared to another, or how long different spiders try to  stay hidden when predators are around. These behaviors can reveal whether a spider  is bold and aggressive or shy and cautious. In a colony, a cautious spider may stay home and make silk while a more aggressive  spider goes out to hunt prey.

And when these different  personalities come together, that can affect the group’s overall behavior. In one study, scientists found that a  colony with a mix of bold and shy spiders showed twice as much defensive  web-making during an attack by predatory ants than colonies where  spiders were just bold or just shy. And research has found that having  a mix of different personalities may translate to more reproductive success.

It’s not just evolutionary biologists who  are interested in collective behavior. The findings could be helpful  for robotics engineers too. For a while now, engineers have been  working on building small robots that can work together in a group.

The idea is to create a kind of mechanical  bee hive or swarm that could do things like work in warehouses, look for survivors  in collapsed buildings, or even explore space. One of the main challenges is in figuring  out how to program and control the robots without one central controller  and without having to give every single robot some super complex AI. These approaches are just  impractical on a large scale.

Which is why engineers are interested  in groups of social animals, like bee hives or spider colonies. One of the incredible things about  them is that they coordinate themselves without any sort of central command, and each individual’s biological  “programming” is very simple. So, studying the simple rules  nature uses to coordinate swarms and colonies could inspire engineers.

And finally, while studying the spiders  may help us understand the benefits of becoming social, it might also  help us understand the downsides. Because it turns out that living in a big ball  of spiders may not be that stable an arrangement. One of the major problems is  that social spider colonies seem to have a lot of inbreeding  and a loss of genetic diversity.

And that gives the colony less  power to survive threats as a whole. Because a disease or a predator that  exploits a weakness in one of them can more easily take down the whole colony. Harmful recessive genetic conditions  may also become more common over time.

In fact, one study found that  in one South American species, one in five colonies dies out  after just one generation. As a result, for spiders, social living  may be sort of an evolutionary dead-end. As some scientists have pointed out,  once a spider species becomes social, it doesn’t seem to diversify, it’s just  stuck on its own branch until it dies out.

Still, even if they’re not the most  evolutionarily successful group ever, social spiders are a  fascinating natural experiment. The fact that they defy our  expectations of how a spider works in so many different ways means  that biologists, psychologists, and even engineers have been  able to learn a ton from them. Sometimes it’s the weird  ones that teach us the most.

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The first 100 people to download Endel using that  link will get a free week of audio experiences! Thank you to Endel app for supporting this  SciShow video and thank you for watching. [♪ OUTRO]