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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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