No Way Home: An arachnologist critiques Spider-Man's powers
Spidey may be a superhero worthy of the Avengers, but are his abilities really within the bounds of what spiders can do?
Spider-Man, Spider-Man – famously he can do whatever a spider can. But how true is that, exactly? How accurate are Spider-Man’s powers compared his real-life counterparts?
“For a start,” says arachnologist Rod Crawford, curator at the Burke Museum in Seattle, “in certain Spider-Man movies he squirts silk out from his hands. Real spiders only produce silk from their spinnerets, which are appendages at the tail end of the abdomen. So if a human carried a spider’s silk production ability, you would normally expect it to come out of the human’s butt.”
With the release of new Spider-Man film No Way Home, Crawford goes through the web slingers’ powers to sort out the Spider-Fact from the Spider-Fiction.
Spider-Man’s super strength is based on the idea that a spider can lift many times its own weight. Therefore, if a human possessed the abilities of a spider, they too could lift many times their own weight.
But Crawford is sceptical of that idea. He cites the square-cube law, a mathematical principle which states that when an object undergoes a proportional increase in size, its new volume is proportional to the cube of the multiplier and its new surface area is proportional to the square of the multiplier. What this essentially means is that as an object grows larger, so too does the strain and demands on that object.
“Strength does not scale directly with size,” says Crawford. “The smaller you are the easier it is to lift large objects because the large object itself simply does not weigh very much. The larger you are the harder it is to lift large objects because the weight of the large object increases a great deal faster than your own strength. Spiders have about as much strength as insects of the same size range, and a spider in a web is able to lift a prey item that weighs a few times more than the spider. But in an absolute sense that item is still extremely light.”
Spider-Man’s reflexes are super-fast, as befitting certain types of spiders. “Some spiders are extremely quick,” says Crawford. “There is a ground spider found only in North America which, in terms of body lengths per seconds, can run in relative terms twice as fast as a cheetah. However, if it was scaled up to human size it couldn't run at all, because of square-cube law.”
And how about movement such as jumping? “Some are good at jumping, some aren’t,” says Crawford. “House spiders are not particularly good jumpers. Jumping spiders are extremely good jumpers.
"Also, spider jumping is done in a quite different manner from the jumping of a being like us that has internal bones in our legs that are surrounded by muscle. Spider legs do not have extensor muscles at all. So when they extend the leg in order to jump, that is not done by a muscle, it's done by hydraulic pressure of blood.
"A spider that's jumping increases the blood pressure in jumping legs to such an extent that if the spider had a doctor that doctor would go through the roof about it.”
There is no single explanation for Spider-Man’s ability to stick to and climb walls. The explanation for the original comic book Spider-Man, for instance, was that he could bond himself to surfaces through an electrostatic force. While in the Sam Raimi Spider-Man movies, Peter Parker is seen growing tiny, razor-sharp hairs from his fingertips, which allowed him to grip surfaces.
In reality, those methods are not a million miles away from how some spiders climb walls. “Any spider can climb a rough brick wall because they have claws,” explains Crawford. “But jumping spiders and some other groups have special microscopic hairs on the tips of their legs that are able to cling to smooth surfaces.”
The hairs of a spider contain hundreds of thousands of even smaller hairs called setules, which can exploit van der Waals forces – the attraction of intermolecular forces between molecules – to create a temporary molecular bond with a surface. Scientists have concluded that this bond is so strong that a spider could conceivably carry 173 times its body weight while attached to a surface.
Spider-Man’s webbing is ridiculously strong. Just take 2017’s Spider-Man: Homecoming, where it’s proven tough enough to prevent a ferry from splitting in two; or 2004’s Spider-Man 2, where it’s stretched to breaking point slowing down a runaway train. And real-life spider silk, explains Crawford, is not too dissimilar.
“A typical spider thread is only a few microns thick,” he says, “and yet for its size it is considerably stronger than something like a typical steel cable. It is probably the strongest natural fibre known.” This is why scientists are attempting to artificially reproduce spider silk for use in bike helmets and single-use plastics.
The sight of Spider-Man using his webbing to swing through a city isn’t as far-fetched as you may think either.
“Spiders do descend from high points to low points on threads,” says Crawford. “They don't do any kind of Tarzan-like vine swing, because they don't have any way of launching themselves, but if a spider is descending on a thread and then there's any kind of a wind blowing, the spider can be moved by the wind in a horizontal direction to land on something that's not vertically below a starting point.”
One of Spidey’s most famous powers is his spider-sense, which gives him the ability to sense danger before it happens – represented by a tingling feeling at the back of his skull.
“Danger is a subjective thing,” says Crawford, who is sceptical of the idea of spiders being alerted to danger before it happens. “That sounds like premonition. And I don't believe there's any research that demonstrates premonition in spiders.”
Real spider senses, Crawford explains, are attuned to their local environment, but do have their limits.
“Spiders have hairs that are extremely sensitive to air vibrations,” he says, “including very specific frequencies of what we would call sounds. They also have what we call a chemotaxis sense, which you might describe as smell by touching. Only a few spiders can detect airborne odours at all.
"And as for their sight, that varies on the kind of spider. Jumping spiders have some of the best vision in the animal kingdom. It’s almost as good as a human's. However, your typical house spider’s eyes cannot form recognisable images at all.”
About our expert, Rod CrawfordRod is Curator of Arachnids at The Burke Museum, University of Washington. He runs a website dedicated to debunking spider myths.
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Stephen Kelly is a freelance culture and science journalist. He oversees BBC Science Focus's Popcorn Science feature, where every month we get an expert to weigh in on the plausibility of a newly released TV show or film. Beyond BBC Science Focus, he has written for such publications as The Guardian, The Telegraph, The I, BBC Culture, Wired, Total Film, Radio Times and Entertainment Weekly. He is a big fan of Studio Ghibli movies, the apparent football team Tottenham Hotspur and writing short biographies in the third person.