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  • [♪ INTRO]

  • Here at SciShow, we love snakes.

  • We've got episodes on venomous snakes, and poisonous snakes,

  • and we've even had some on SciShow as Talk Show guests.

  • But you might still think all snakes are basically the same.

  • You know, like, they're all just, like, this slender, muscular danger noodle.

  • So in this episode, we want to pay special tribute

  • to the incredible diversity of these legless creatures.

  • We're going to talk about 6 snakes with some extraordinary features.

  • Hognose snakes get their affectionate name from their enlarged rostral scale,

  • which is the plate at the front of a snake's nose.

  • That gives them their upturned noses which make them look,

  • you know, kind of cutely pig-ish.

  • And kinda like a pig's snout, their little snoots are great for rooting around in the soil.

  • The upturned nose acts as a shovel to move soil or sand out of the way as they make a safe burrow.

  • The snakes will bend their heads downwards and then wiggle them from side to side.

  • At the same time, their bodies move in wave-like motions to help them sink below the dirt.

  • Those piggish noses also help them find food.

  • They eat everything from lizards to small mammals, but a nose for digging

  • helps them most if they're looking for frogs and toads that spend part of the year underground.

  • Their fangs, which, like other rear-fanged snakes,

  • are located further back in their jaws than front-fanged snakes, are long and smooth,

  • so some scientists thought that they might be used for popping toads

  • that inflate themselves as a defense mechanism.

  • But a scientist back in 1976 measured how long the fangs would need to be,

  • 1.38 cm on average, in case you were wondering,

  • which is much longer than the fangs actually are.

  • They're only about 0.3 - 0.5 cm.

  • The hognoses's unique hiding and hunting behavior is pretty cool,

  • but they have another trick up their scaly sleeves.

  • When they feel threatened, they'll roll over on their backs and play dead, also called death feigning.

  • And hognoses really get into this dramatic act.

  • They will writhe around and stick out their tongues until whatever scared them is gone.

  • Way back in 1974 scientists noticed the snakes' heart rate would also drop while death feigning

  • from around 50 to 80 beats per minute to between 3 and 15 beats.

  • That is some dedication as a method actor!

  • Stiletto snakes might sound fashionable but that name

  • isn't because they have good taste in high-heels.

  • They are a burrowing group of snakes found mostly in sub-Saharan Africa.

  • There, they inhabit everything from deserts to rainforests.

  • And they're best known for their long, knife-like fangs that allow them to

  • stab prey without opening their mouths.

  • Most snakes strike when their potential meal is right in front of thembut not stiletto snakes.

  • They'll slide up past an unsuspecting skink, lizard, gecko or mouse

  • and then whip their head backwards to lodge one of those long fangs in the prey.

  • It's such a unique movement done at close range

  • that some scientists prefer calling itfang stabbingrather than striking.

  • And it might sound like a weird way to hunt, but it's actually really useful

  • as it lets the snakes capture prey in tight spaces like tunnels or burrows.

  • It also allows them to release the prey really quickly,

  • because they don't have their whole mouth wrapped around it.

  • And that's important because some of the stiletto snakes' prey,

  • like scaly lizards, tend to fight back.

  • So they want to get in, deliver some venom,

  • and then back off until the toxins have done their job.

  • In fact, the snake's entire mouth is specifically adapted for this weird attack.

  • Stiletto snakes have a short jaw bone, fewer teeth,

  • and a snout that's tightly attached to the rest of the skull

  • so the jaw stays clamped closed when it's wiggling through tight spaces.

  • But this awesome ability and anatomy has its downsides.

  • Stilettos lack the teeth needed to do the usual pterygoid walk to swallow their prey.

  • That's where a snake will open its mouth and use specific teeth to hook

  • and then pull prey into its mouth step by step.

  • Which makes sense if you don't have, like, hands to shovel food in your mouth, like, awww, I do.

  • And even if they had those teeth, their jaws don't open wide enough to swallow food that way.

  • So stilettos have to do a weird head wiggling action where they shift their jaw backwards,

  • flex their head down toward their belly and squeeze their trunk forward,

  • then shift their jaw and head forwards over their prey.

  • It sounds pretty awkward if you ask me.

  • And according to scientists this is pretty much as extreme as this adaptation can get.

  • Basically it can't really improve upon its unique strike without sacrificing the ability to eat.

  • The Pseudocerastes snakes of the Middle East range from southern Israel,

  • through Iraq, southwestern Iran and Afghanistan and Pakistan.

  • They get their scientific name from the false horns on the top of their heads,

  • but it's what's on the other end of the snake that's more interesting.

  • You see, vipers are ambush predators.

  • They select a good hiding place and then wait for prey to come by.

  • Even with the perfect location, though, it can take a bit of time for the right meal to

  • get close enough, so these vipers wag their tails around as a lure to draw their prey in.

  • And one of these snakes, the Iranian spider-tailed viper,

  • has arguably the most elaborate tail lure of all.

  • Most of its grayish brown body blends in almost perfectly

  • with the gypsum rocks common to its habitat.

  • But its tail looks just like a spider, and with some careful jiggling back and forth,

  • it would probably have you fooled too.

  • But don't worry, it's birds that this spider is after.

  • The good news is that I, personally, am not ever attracted to a spider on the ground,

  • so I'm probably not gonna get lured in by this.

  • But birds do have to be worried.

  • These snakes seem to mainly hunt larks, shrikes and warblers,

  • but have also been known to catch the odd gecko, too;

  • basically anything that goes for that tempting tail.

  • But, there are some issues with a lure that is so convincing.

  • Researchers have found snakes with damaged tails,

  • presumably because some birds actually bit thespider”.

  • It's unclear whether this makes the snakes any worse at luring in prey.

  • But I bet it doesn't feel too great to have part of your tail bitten off!

  • Hunting underwater comes with an entirely different set of challenges

  • than the snakes that we've talked about so far.

  • Like for example, finding your prey when the water is slow moving or not very clear,

  • or striking with enough power to counteract the resistance of the water.

  • But the tentacled snake seems to make light work of it.

  • This species can be found in slow moving rivers and murky ponds in southeast Asia,

  • where it feasts almost exclusively on fish.

  • The snake will sit motionless in the water in a kind of J shape and wait for fish to approach.

  • It will then move sections of its body to herd the fish up towards its jaws.

  • When the fish is positioned in a little crook between the snake's head and body,

  • the snake will whip its head sideways to strike,

  • turning its head to meet the fish front on at the last moment.

  • This is different than most other snakes, which coil up their bodies and strike forwards.

  • The tentacled snake will even preempt the fish's escape.

  • It strikes where the fish will be, not where it currently is.

  • Though scientists aren't yet clear whether it's back and forth evolution

  • between predator and prey or individual experience that led to such smart targeting.

  • The snakes possess some awesome features that facilitate this unique attack.

  • Probably the most distinguishing one is those little tentacles

  • that jut out from the sides of the snake's nose.

  • They are highly sensitive to changes in water around them.

  • They're stuffed full of nerves that send signals to the snake's brain

  • when anything within a two centimeter radius of them moves.

  • That's exactly how close a fish is when the snake would want to strike.

  • The snake's shallow, flattened skull is thought to help it hunt underwater

  • because it minimizes drag as the snake strikes,

  • allowing it to attack with the same, or even more force, as land snakes.

  • That's pretty remarkable considering it's pushing against water instead of air.

  • It also helps that the snake can engulf the water ahead of it

  • when it strikes instead of pushing it out of the way.

  • Now, you may tremble at the idea of any snake slithering towards you,

  • but what if the snake was, like, flying through the air?

  • So-called flying snakes of the genus Chrysopelea are sometimes called

  • the only limbless vertebrate flyers.

  • But flying is a misnomer. They're actually gliding.

  • I'm not any less scared of them.

  • These tropical southeast Asian snakes will launch themselves off a high perch,

  • slither through the air to land some 8 to 16 meters away.

  • That's pretty impressive given the snakes are only around half a meter to just over a meter in length.

  • In the mid 2000s, scientists filmed the paradise tree snake species

  • as they launched themselves from a platform, and then reconstructed those jumps

  • in three dimensions, to figure out exactly how the snakes were moving.

  • Let's start with takeoff, which is kind of a hard thing to do without legs to push with!

  • So, the snakes make a J shape with the front part of their bodies

  • while hanging from their tails, and launch themselves that way.

  • They then enter a falling phase for a short while before leveling out and gliding,

  • all the while undulating their bodies in a complex side to side pattern.

  • They can even turn in midair! Talk about falling with style!

  • And this movement is pretty different from what snakes do on the ground

  • so scientists think that this special wiggling might help them

  • generate lift or stabilize them while gliding somehow.

  • Some of their ability to glide also comes from the way

  • the snakes flatten their bodies horizontally once they're in the air.

  • The flattening functionally turns their bodies into a wing,

  • which separates the air in front of it into two streams: one above the body and one below.

  • The difference in pressure between the air that goes under the snake

  • and over the snake can generate lift, just like an airplane wing!

  • But scientists aren't 100% sure why these snakesfly”.

  • It's not more energy-efficient than wiggling along the ground,

  • but it is quick so it might help them escape predators better.

  • Either way, if you see one of these snakes slithering towards the end of a branch,

  • I would move out of the way.

  • The olive sea snake spends its time swimming around the coral reefs of Northern Australia,

  • Papua New Guinea, and New Caledonia using its paddle-like tail to propel itself through the water.

  • Its long, skinny body lets it squeeze into crevices in search of crabs, prawns, fish eggs and fish.

  • But it's not the only hunter in these waters, so it often ducks into those same crevices to hide.

  • In fact, aside from surfacing for air, courting a mate and, of course, nabbing some food,

  • they usually spend their time trying to fit as much of their 1.2 meter long body in coral as they can.

  • There's only one problem with that.

  • If the snakes' tail peeks out, it risks getting chomped on.

  • So the olive sea snake has evolved a really neat way of keeping an eye on its tail. Literally.

  • The skin on its tail can sense light,

  • which means the snake can adjust if itseesits tail sticking out.

  • Scientists first studied this ability in the late 1980s

  • when they kept ten snakes in a darkened lab tank.

  • They noticed that the snakes pulled their tails in

  • when researchers shined a fiber optic light on them.

  • This phototactic response only worked when the light shone on the tip of the tail

  • not the part closer to the rest of the body.

  • Then, in a study published in 2019,

  • researchers looked to see if other sea snakes also had this ability.

  • They found that two other species of sea snake showed a similar response to light,

  • and since they were close relatives of the olive sea snake,

  • the researchers concluded that this ability probably evolved in their common ancestor.

  • That may mean that 10% of all sea snakes sense light with their tails!

  • By using RNA sequencing, the scientists figured out that their tail skin

  • expresses genes which code for a light sensitive protein called melanopsin

  • and also other proteins involved in how light receptors sense light levels,

  • which might explain how they actuallyseewith it.

  • So you see, snakes aren't just muscle-y danger noodles.

  • Whether it's being a really talented actor, gliding between trees

  • or having a tail that looks like a spider, snakes are super diverse.

  • And hopefully, understanding these animals and their weird,

  • unique adaptations will help us all appreciate them a little more.

  • Thanks for watching this episode of SciShow!

  • We put out educational science videos like this every day,

  • so be sure to click that subscribe button to get them all into your feed.

  • And if you liked learning about these awesome snakes,

  • you'll probably love our episode on 7 uniquely fierce sharks!

  • I mean, I'm not, like, telling you what to do or anything,

  • but if it were me, I'd watch that one next.

  • [♪ OUTRO]

[♪ INTRO]

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B1 中級

從霍尼克斯到蜘蛛尾巴。6條高貴的蛇 (From Hognoses to Spider Tails: 6 Sublime Snakes)

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    林宜悉 發佈於 2021 年 01 月 14 日
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