Thanks to Linode, a top-rated cloud computing company with over a million clients, for supporting this episode of SciShow.

Head to linode.com/scishow to learn more and to get a $100 60-day credit on a new Linode account. [♪ INTRO] Whether you consider spiders friend or foe, you’re probably relieved they typically come in pretty small packages. Sure, some species look huge next to your average spider, as in, large enough to catch and eat small rodents.

But that’s nothing compared to Earth’s enormous blue whales or meter-long salamanders. On a planet home to some super-sized species, what’s keeping spiders so tiny? And is it possible to breed giant versions, you know, if ever we wanted to?

There are many limiting factors that keep some critters small, like access to available resources. As a general rule, how much food, suitable habitat, and other resources are available play a major role in the number of individuals that can survive in a given place. So populations of giant spiders sharing the same environment might not have enough resources to go around.

And even if larger spiders weren’t directly competing with each other, they would definitely need to eat more, which could mean starvation if food becomes temporarily scarce for any reason. Plus, the denser a population is, the smaller an animal tends to be, which makes sense for spiders. You might have noticed they are pretty much… everywhere.

So their abundance could also be influencing their size. So our eight-legged pals have all these checks and balances influencing their slight stature. But say we dream big and we could account for all these external factors.

Would it still be physically possible to breed giant spiders? Well, probably not, simply because of how spiders breathe. Spiders have a very slow metabolism, so how they turn their food into energy is pretty sluggish, even in comparison to other animals of similar size and activity level, like insects.

And it works just fine for them since many spiders are mostly sitting around waiting until food wanders into striking range as opposed to actively hunting. This slow metabolism appears to be tied to how much oxygen their respiratory system can take in. Spiders keep their respiratory system in their abdomen, which typically includes a number of tracheal tubes and book lungs.

This type of lung has stacked air pockets, making them look like, well, a book! And just like regular books, their whole respiratory system comes in many shapes and sizes, but spiders can’t actively draw air in and out of these lungs like we do; instead, oxygen diffuses into the blood as air flows through the book lungs’ pockets, and sometimes from their tracheal tubes too. Larger critters need to be able to send enough oxygen to their larger number of cells.

And since air passively flows through their system, spiders would need a lot of oxygen cycling around to get very big. Plus, Earth’s air is only about 21 percent oxygen. Unless our atmosphere changes dramatically, how they breathe is a major limiting factor.

In the end, with so many variables at play, we just don’t know how large a spider could get. Thanks to our patron, Andrew Kawam, for asking this awesome question! And I think it’s safe to say you won’t be running into any car-sized spiders anytime soon.

But you can rest at ease when working on huge computing projects thanks to today’s sponsor, Linode. Linode is a cloud computing company that provides you with products like Linux servers with free firewall and networking tools to get your ideas live on the internet as quickly and simply as possible. People turn to the cloud to simplify processes and make them more affordable.

But some cloud computing companies have the opposite effect, with surprising bills and giant overwhelming bundles. Linode is the alternative for small businesses and independent developers who only want the services they need and for the same price every time. For more on Linode, click the link in the description or head to linode.com/scishow.

That link gives you a $100 60-day credit on a new Linode account. Thank you for watching this episode of SciShow, and thanks to Linode for sponsoring it. [♪ OUTRO]