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Whether it’s building bridges across rivers or solving puzzles, spiders are way cooler than you might think. Many have smart or elaborate features that allow them to do some pretty extraordinary things!

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When you hear the word spider, you might immediately think venomous, terrifying, or just... nope. Or you could be like me, and think they're amazing!

Very few spiders are actually harmful to people, while lots of spiders, pretty much all of them, in fact, are helpful to us in some way. When you look at spiders more closely, you realize they have some amazing abilities that may lead to really useful things like tougher fabrics or stickier glues. So in honour of these eight-legged creatures, here are eight spiders that push the limits of biology.

Net casting spiders in the family Deinopidae are sometimes called ogre-faced spiders because of their two huge forward-facing eyes. In one species, these eyes can reach 1.4 millimetres in diameter. And while might not sound big, that's the largest eye relative to body size found in spiders, about a tenth the length of their entire body.

It would be like you having eyes bigger than cantaloupes. These eyes give the spiders a wide but shallow view of the world, kind of like looking through a fish-eye lens. They also contain lots of light receptor cells, allowing them to pick up around 2000 times more light than the eyes of day-dwelling spiders or humans.

But seeing that much light during the day is problematic, so they actually destroy parts of their retinas every day and rebuild them again just before nightfall. These special eyes are what allow net-casting spiders to, well, cast nets. Though they technically build webs, they don't use them like other web-builders do.

Instead of making a big mesh net for a bug to run into, they spin a small web between their legs. Then, in the dark of night, they drop down on their prey from above and envelop them with their sticky net. Scientists think the spiders' net casting hunting technique, along with those massive eyes, evolved during the Cretaceous period as a way to get prey that could now run.

And now, they're inspiring sensor designs. Since the spiders' eyes are so good at picking out targets and detecting motion in low light, engineers are hoping understanding how they work can help develop sensors that do better in complex, dark environments. Pelican spiders are pretty easy to identify even if you're not an arachnologist.

That's because attached to their weird ballooning heads are two menacing claws which, at rest, look kind of like the bill of a certain water bird. Now, all spiders have these mouth-related appendages, called chelicerae. They're the parts tipped with fangs.

But pelican spiders have evolved the longest chelicerae of any spider, and they use them to ruthlessly hunt their 8-legged cousins. First, a pelican spider has to find and creep up on its target. So, it uses its legs to feel for web trails, the long strands of silk that spiders leave to find their way back to their web, or draglines, the stronger, outer edges of the web.

This stalking process can take several hours. Then, when a tasty spider is within arms reach, the pelican spider juts out its chelicerae at a 90 degree angle, impaling its victim and delivering a fatal dose of venom. And that's not the most gruesome part.

The pelican spider will usually just leave their prey hanging there, struggling around, for half a minute or so until the venom has done its job. Despite their unique look, not a lot was known about these spiders until recently. In January 2018, a biologist from the Smithsonian Museum described 26 species of this spider, including 18 new ones.

And that's helping scientists figure out how pelican spiders' unusual traits evolved and diversified over time. Darwin's Bark Spiders spin webs that hold not one, but two official Guinness World Records. They've got the largest webs because their webs can be up to 2.8 metres across.

And they're the longest webs, too, because their bridge lines, the tough strands which form the basis of the webs, can be up to 25 metres long. Such uniquely big webs are thanks to a special silk that's the perfect combination of strength and stretchiness. All spiders make the structural part of their web from what's called dragline silk, which has a protein core covered with a thin sugary protein layer and a fatty outer coating.

But the dragline silk from a Darwin's Bark Spider is two times more elastic than other spider silks and 10 times stronger than Kevlar. And that allows them to spin webs where other spiders can't: across rivers. Their oversized cobwebs span waterways and grant them access to a bunch of flying insects that other spiders can't reach.

And because of the strength of their webs, they can even catch small vertebrates. Their super strong and stretchy silk may even save human lives one day. Scientists are currently trying to figure out exactly how the spiders make it in the hopes of creating a synthetic version, which could lead to better bullet proof vests or other high-performance materials.

The Mygalomorphae infraorder of spiders, which includes tarantulas and trapdoor spiders, may have found the secret to a long life: stay indoors and never change. Other spiders rarely make it more than a few years. But tarantulas can make it into their 20s, and Number 16, an unceremoniously named trapdoor spider, made it to the ripe old age of 43 before she died in October of 2016.

Scientists think they live so long because they spend their lives in stillness and solitude in underground burrows. Trapdoor spiders even seal themselves in with a well-camouflaged door made of a cork-like material. And that means, a lot of the time, they just kind of hang out in their home while they wait for a meal to come along.

Staying in keeps them safe from most predators and other threats, like dehydration. Their restful hunting style also means they need to have a low resting metabolic rate. Their basic cellular workings need to be pretty energy-efficient so they don't burn through all of their fuel reserves before they can stock up again.

And there's a theory that a low resting metabolic rate means a longer life because using up energy creates damaging molecules called free radicals, so less energy use overall means less damage to cells over time. Biologists don't think that that's the whole story to their longevity, though. They're still figuring out how metabolic rate, free radicals, body size and aging all fit together.

And that information could help them unlock the secrets to longevity in people, too. This next spider takes prey capture to a whole new level of weird. The spider family Scytodidae spit to immobilize their meals.

Most spiders make silk in glands at the rear of their abdomens. But, when their prey is 2 centimeters or less away, a spitting spider unleashes a spray of liquid silk from the venom glands in its chelicerae. The spit is forced out thanks to a buildup of pressure that comes from having large venom glands and a tiny muscle at the base of those glands that squeezes when it's time to fire.

While spitting, the spider wiggles its chelicerae from side to side at a rate of 1700 times a second to spray a zig-zag pattern. And the silk becomes sticky when it comes in contact with the air, pinning the prey down. This whole spit attack happens in one seven-hundredth of a second.

The spider can even regulate how much spit it sprays depending on the prey's size and how much its likely to struggle. Once its meal is firmly glued down, it will sidle up and inject its prey with venom to fully immobilize it before actually eating its meal. Scientists are still debating about whether that initial spit contains venom that immobilizes the prey or if it's just a kind of glue.

On the one hand, the spit is made in venom glands which have the ability to make both venom and sticky silk. But prey don't look like poisoned when they get shot, so the glands could be making silk and venom at different times. And research to settle this debate isn't just to prove who's right.

Figuring out what's actually in their sticky spray could help engineers develop better adhesives. As you've probably heard before, brain size isn't everything when it comes to intelligence. That's particularly true for the fringed jumping spider, a spider with a brain the size of a sesame seed that plans and fine tunes its strategy with every hunt.

They're found in parts of Australia and Southeast Asia, and they have to use their smarts to catch their prey, other spiders. They use what's called aggressive mimicry, kind of a wolf in sheep's clothing approach. A fringed jumping spider might pluck the edge of a spider's web to create the exact same vibrations as a caught insect, for example.

Or, it might hide itself in a leaf and vibrate its body to mimic other species' courtship displays. And which approach it takes doesn't come down to chance. The spiders can plan ahead and change their strategy if an approach doesn't work the first time around.

Scientists have shown their smarts in the lab too. These spiders can navigate and plan routes through mazes, and they can find their way to a tasty snack after only seeing the path briefly. They've also been known to use trial and error to escape from a platform surrounded by water, rather than just using the same, failing method each time.

Some scientists think they developed such smarts as a part of an evolutionary arms race between them and the spiders they eat. But the piece of the puzzle that's missing is an understanding of just how these clever spiders are able to do the things they can. Researchers are now studying their teeny brains in the hopes of learning more about the neural basis for intelligence.

Ponds and streams contain a lot of potential prey, if a spider if is willing to get their feet, or rather their whole body, wet. And that's why some spider species will venture into the water on occasion, but there's only one that lives almost exclusively underwater: the diving bell spider. They can be found in slow moving streams, ponds and swamps from Europe through central Asia.

And they spend almost all of their lives below the surface, even though they can't actually breathe water. Instead, they spin a special web between underwater plants with three different types of silk fibers, and then drag air from the surface to fill the space underneath it. Diving bells do all sorts of things in their web-bubbles.

They eat, sleep, and mate. And when they're hungry, they can actually swim around for a little bit in search of prey thanks to the fine, water repellent hairs on their bodies. These hairs hold onto a little bit of air, which acts like a scuba tank of sorts.

You see, spiders breathe through small holes called spiracles on the underside of their abdomens that connect to their lungs. As long as these holes are covered with air, they can breathe, even if the rest of their body is submerged. And diving bells can tolerate lower levels of oxygen than their kin, so they can swim out of their bubble homes to grab a quick bite to eat without drowning.

In fact, they'd probably live their entire lives underwater, except the bubbles in their webs slowly shrink. So, once a day or so, they have to surface and bring down a few batches of fresh air. And understanding how they create their little bubble homes could lead to better materials for underwater use.

Scientists are hoping analyzing the structure of the different threads they use can help us make things that stay glued when they get wet. You might have seen this last spider lurking around your home, but you probably didn't know it was also an official world record holder. The giant house spider held the Guinness World Record for fastest spider until 1987 when it was replaced by members of the arachnid order Solifugae, and those aren't true spiders, so I think it should have kept its title.

Giant house spiders can run as fast as half a meter per second, or 1.8 kilometers per hour. Which, OK, means it's only about a tenth as fast you are, but proportional to its size, that's the same as you running 55 meters a second. Giant house spiders run by alternating the movement of their pairs of legs, two pairs stay on the ground and support the body while the other two move forward.

And their super fast speed largely comes from having really long legs. Their leg span can reach as much as 10 centimeters. They likely developed such speed because they don't rely on sticky webs.

Like other funnel-web spiders, giant house spider webs are relatively flat with a funnel at one end that the spider hides in. And they aren't sticky, so they just trip things up a bit, and send vibrations to the spider that alert them to a potential meal. The spiders then rush out to attack, using venom to subdue their prey.

Before you get too worried: that venom, while deadly to bugs, is basically harmless to people. And try to keep in mind: if you see one of these spiders running, it's probably running away from you. In their eyes, you're the scary creature.

Since their legs are so important for running to catch their food, house spiders can actually regrow them if they get chopped off. And studying how they do that could help us figure out how to grow our own organs or limbs in the lab one day. Whether it's building bridges across rivers or solving puzzles, spiders are so much more than just annoying or spooky creatures on the ceiling of your room.

Many have smart or elaborate features that allow them to do some pretty extraordinary things like spend a day underwater or destroy and regrow their retinas. And by studying them, we might just learn a few new tricks, too. Thanks for watching!

If you liked this episode on incredible arachnid abilities, you might like our list of 7 unbelievably hardcore ants. [♪ OUTRO].