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How Spider-Sense Works

This episode of Because Science is brought to you by Destiny 2: Forsaken. I have a confession to make, I've been trying to scienceSpiderman for years now and every time I havebeen asked to look into the so called Spidey-sense, I've dismissed it out of hand without ever really looking into it. And now that I have, I have to apologize. I was so wrong. Spiders have tarsal claws down some of the most amazingsenses of any organisms on this planet. If Peter Parker had spider senses, they would definitely make him amazing. Ooooohhhhh.



Spiderman's Spidey-sensehas been a part of Peter Parker's webatoirsince the hero first swung into the pages of Marvel Comics all the way back in 1963. Since then, comics, movies and video games have depicted spider-senseas a feeling or premonition that something is about to happen or that something,somewhere is going wrong. It's an almost magical sixth sense without a solid biological backing. Like I said, you don'thave to look any further than real spider sensesto make Spidey-sense make sense, sense. So let's ignore theweird precognitive stuff in the name of science and give this powerthat biological backing.



Spiders and many otherterrestrial arthropods like crickets, have threemain sensory systems that could add up totheoretically give a spiderperson a spectacular sense of their surroundings. Two of those systems use tiny hairs to detect touch and motion, tactile hairs and trichobothria. The third uses a fascinating little organ called slit sensilla. Let's start with the tactile hairs, as they are the closest thing to a sense that we are familiar with. Oh you're a big boy. The most common sensorystructures in the animal kingdom aren't eyes or ears, they are hairs. Most of the human body iscovered in hair of some type and all of those hairs add up along with other receptors in your skin to give us an exquisite sense of touch. We can feel if even asingle hair is disturbed.



Ooh, excelsior. We mostly hairless apes have about 60 hairs per square centimeterof surface area of skin. Which makes our sensitivityto physical disturbance, our mechanoreception, pretty good. Spiders though, are on another level. They have around 40,000hairs in the same amount of surface area and theyhave up to three nerves per hair for sensation,whereas we only have one. Wow. Hey if you were that big, how are you even breathing right now, cause I'm pretty sure ifyou scaled up your volume based on your... These thousands of spider tactile hairs, like human tactile hairs, will trigger a sensation in the animal if they are deflected a certain amount. Like pushing or pulling a simple lever. The threshold of force thoughthat will trigger a response from a spider is unbelievably small. A spider's tactile hairswill respond to a force less than half a micronewton.



This is only five times more force than a hydrogen atom'snucleus puts on it's electron. It's hard to even conceptualizehow gentle that is. So if Peter Parker's hairs somehow mutated along with the rest of his body to become as numerous as a spider's hairs and acquired this kindof extreme sensitivity, it would be the first part ofan impressive spider-sense. Sorry. From our perspective itwould be like he's able to feel touches before they even happen. Sorry. Spider-like tactile hairswould make Spiderman intensely attentive to touch, which would be a good place tostart for a real spider-sense especially considering that in the movies, we've seen Peter Parkergrow spider-like hairs. But spiders other sensesare even more impressive.



They can feel things thataren't even touching them. The second spider sensingsystem is trichobothria or hairs that feel forfluid flow, like moving air. These hairs look likethe spiders tactile hairs and they're even locatedin the same place, but these are evolved to feel for even the slightest breeze and I do mean slightest. For example, trichobothriaare so sensitive, they can pick up the minuteatmospheric disturbances that a flies wings produce from up to a few body lengths away from a spider. This would be such as you beingable to feel your friend wave at you from across the space . Oh he is friendly, that's nice. This air-hair isn't just reallyresponsive spider stubble, it is, as one review byFreidrich G. Barth put it, one of the most finelytuned biological sensors in all of nature.



Modeling trichobothria as simple levers, scientists have estimated that the amount of energyit would take to elicit a response from thesehairs is on the order of 10 zeptojoules. I've never even said thatprefix out loud before. This is in theory so little energy that a spider'strichobothria would respond to a laser pointer. It would respond to the pressure of light. Less friendly, ahh!  What he saw was something like this. The pollen particles weremoving around randomly when he assumed they should be still. Cut to 78 years later and thesmart boy, Albert Einstein, publishing a paper thatdescribed this motion. Einstein argued that thepollen particles were being batted around randomly byphysical atoms and molecules in the water, moving around randomly.



At that time, in 1905,the physical existence of atoms and moleculeshad not yet been proven. Einstein's findings wereeventually confirmed and accepted and thiswas one of Einstein's first great contributions to science. Today the random motionof atoms and molecules in a fluid is called Brownian Motion, in honor of Robert Brown. And I told you thatstory to tell you this, spider trichobothria are, in theory, sensitive enough to feel Brownian Motion. To feel, against theirhairs, the individual impacts of atoms and molecules. This represents a spider-sensethat is an almost perfectly evolved material interactionat the very edge of physics. Real trichobothria couldplausibly play a huge part of a real spider-sense.

Being able to feel your enemiesmove through the atmosphere at a distance would be a huge advantage but the last arachnoid sensewould take all of this biology from spider to super. The final component of aspider's sensory system are the slit sensilla, which are mechanoreceptory organs in the spider's exoskeletonthat are unlike anything that we humans feel with. These organs sound fancy butthey actually are rather simple In the spiders legs, near the joints, there are rows of parallel channels where the exoskeletonhas been thinned out. If the spider's leg moves or bends in response to some vibration or force in the substrate or groundthat the spider is standing on or touching, these slit sensilla will deform like accordions. By now, it should not surprise you that the amount of vibrationit takes to alert a spider is astonishingly small. Scientists have found thatthese sensilla can alert spiders to forces near them that are as small as point zero one micronewtons.

This is less than half apercent the body weight of a single cockroach. That means, that if I wereto just take a single step I would...oh, I guess I'm...ahhhhh! Basically if a nearby force or vibration moves a spider's legs atall, it's going to feel it. If I was moving around next to it, a spider about that sizewould be able to feel if I caused it's legs to bendjust a billionth of a meter but that's so small it's hard to visualize so let's increase the spider size. Bigger. Bigger. Bigger. Bigger. Keep going! If that spider got big enough that it was over 100 kilometers across, that it could reach upwith one of it's legs and touch space, it would still be able tofeel if any one of it's legs deformed, literally that much. Just a single millimeter or a millimeter Parker. Argh.

If whatever mutations Peter Parker got from that radioactive spider indeed enabled him to do whatevera spider could do, then I think that using anarray of arachnid sense systems web-head could absolutelyapproximate a sixth sense, at least as sensitive ashuman eyesight or hearing. Slit sensilla scaled up to human size might be able to pick upan approaching bad guy or at least a rampaging rhino. Trichobothria on Spidermanmight be able to pick up the minute atmospheric disturbances from an incoming projectile or even the pressure from the light of a gunman's laser site,which is ridiculous. Real spider senses operate at the limits of the physically possible and if that doesn'tsound like super powers, I don't know what does. So, how does spider-sense really work?

Well I don't think youhave to look any further than the arachnids themselves. Spiders have some ofthe most delicate senses in all of biology and if Peter Parker had them, I think he could approximatesomething like we see in the comic books and the movies. Of course, he would have to find a way to make those tiny hairswork underneath his suit and sure, slit sensillaare only in exoskeltons and not endoskeletons like we have, but being the science wiz that he is, I bet that Parker couldfind a work around, because if he was truly a spider man, he would feel so good, Mr. Stark. Because science.

Everyone gets one right, yeah! Oh, oh why is it hot? Oh it's like al dente spaghetti. (techno music) So let's say that you werea more realistic version of Spiderman and let's sayyou were, I don't know, in New York and a giantspaceship appeared over New York, which would feasibly cause agiant atmospheric disturbance, perhaps if your hairswere like spider hairs they'd stand up on end like trichobothria. Oh wait, does that happen? Confirmed.

Thank you again to Destiny 2: Forsaken for sponsoring thisepisode of Because Science. Destiny 2: Forsaken introducesnew mechanics, weapons, gear and powers for allthe new Destiny players to rise up against the Cabal and take back what is theirs. Forsaken pumps up the chaos and mayhem to a whole new levelincluding nine, yes nine, new super abilities to choose from. Bring the pain down witha new devastating hammer or throw flame daggers toeviscerate your enemies or teleport around them andrelease a monstrous blast and so much more.

Another addition Forsakenis bringing to Destiny 2 is the bow and arrow for preciseannihilation of your foes. Boost your character with new exotic gear to get that edge in the arena. All of this with new areas to explore, new raids and a brand new Gambit game mode makes this a must-have for allhardcore Destiny 2 guardians. Pick up Destiny 2: Forsaken, right now. Thank you so much for watching, Celia. Thank you so much to Phil Torres for his help on this episode. He discovers new speciesof spiders in the Amazon and I'm totally jealous.

If you want more of me, check out nerdist.com or Alpha at projectalpha.com where if you go now you can sign up for a free trial, get this show two daysearlier than anyone else. If you are on Facebook, like this video. If you are on YouTube, like and subscribe and hit that notification bell because we get up to a lotof fun stuff on this channel not just these episodes butalso vlogs and live streams and if you want more social content, follow me and Because Science, here. Thanks! Whaaaaa! 

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