Spider-Man vs. True Spider Superpowers
for National Geographic News
|June 30, 2004|
Photo Gallery: Spider Power
Fast Facts on Spiders
With Spider-Man, the world's most famous web-slinger returning to the movie screens today, spiders everywhere may be readying their webs for a bit more attention. But how do our red-and-blue hero's capabilities compare with the superpowers of real spiders?
Spiders aren't swinging their way through the skyline or facing up to crazed criminals like Doc Ock, the villain in Spider-Man 2. But they've got the wherewithal to survive in a range of environments that gives them their own extraordinary edge.
Many species of jumping spider, found all over the world, can bound as much as 50 times their body length. Right now, U.S. long jumper Mike Powell holds the world's record with a jump of 8.95 meters (29 feet, 4.5 inches). If the six-foot-two (1.9-meter) Powell had a jumping spider's hopping capability, he might be able to leap 300 feet (90 meters).
Jumping spiders use these fantastic leaps to snatch unsuspecting insects. "They hunt down prey, and then they'll pounce on it," said Andrew Martin, from the Institute of Technical Zoology and Bionics at the University of Applied Sciences in Bremen, Germany.
How Spiders Walk on Ceilings
Some spiders have another seeming superpower: an ability to adhere to sheer surfaces, even when upside down. To find out how they do this, Martin and colleagues studied the foot of a jumping spider, Evarcha arcuata, through an atomic force microscope.
The spider's foot is covered with hairs, or setae, that branch into ever smaller hairs, or setules. Through their powerful microscope, the team studied the forces acting on a single seta. They calculated that the grip of the jumping spider is so strong that it could hold 170 times the spider's own body weight before coming unstuck. That would be the same, Martin said, as Spider-Man lugging 170 people from danger while clinging to a building with his fingers and toes.
What's at work in real spiders are van der Waals forces, caused by moving electrons that create hot spots of attraction between nearby molecules. With these miniscule charges acting on the 600,000-plus setules in each furry seta, a spider can hang upside down on a leaf or a wall with ease.
The unusual thing, Martin said, is that the spider's clinging ability resembles that of a gecko more than that of an insecteven though eight-legged spiders are much more closely related to six-legged insects than to lizards. "From a biological point of view, that was pretty astonishing," he said.
The team, which published its findings this spring, hopes the secret of the spider's stickiness can be adapted for human usessticky notes, boots for astronauts, even gloves for soccer goalies.
Weaving a Web
Martin, who confesses he's "not a huge Spider-Man freak," said the movie's web-spinning wonder's powers aren't the same as those of real spiders. "Spider-Man works in a completely different way," he said.
The most familiar of the world's 37,000 spider species may be the orb weavers, spiders that create the wagon-wheel web designs featured in dewy photographs and eerie haunted houses.
Orb weavers, like the golden silk spider Nephila clavipes, spin webs out of spinnerets, organs with precise muscle control found on the spider's abdomen. With the spinnerets' muscles, spiders can open and close the silk ducts and control the thickness of the silk they spin.
Some spiders have as many as seven types of silk, each used for a different purpose. For a wheel-shaped web, the main components are usually dragline silk, a tough thread that makes up the web's scaffolding, and sticky silk, which forms the net to snare a spider's next meal.
This combination is ideal for catching prey, said Todd Blackledge, an entomologist at the University of California, Riverside. "When a fly hits the web, the sticky silk cushions the impact and traps the fly, but the stiff dragline silk absorbs the force and keeps the web intact," he said.
The female N. clavipes produces dragline silk that may be even better at absorbing impact than steel and Kevlar (a brand of protective fiber used to make bullet- and fire-resistant apparel).
Silk isn't used only for webs. Like Spider-Man, spiders can use their silk to travel from place to place using dragline silk. A spider might also employ another silk type, a glue like silk used to connect separate threads, to gain serious distance. "If a spider needs to jump, it might secure its dragline first with this joint cement," Blackledge said.
Other silks are used for forming egg sacsa trick our hero won't likely needand wrapping up prey.
Some spiders get artistic with their webs. Blackledge has studied several species, including the black-and-yellow garden spider and the banded garden spider, which incorporate designs like spirals and crosses into their webs.
These camouflaging designs, called stabilimenta, may be defenses against predators, Blackledge said. In his work, he found that the number and complexity of the designs depended on how hungry the spiders were.
When spiders weave designs, they may be well camouflaged, he said, "but at the same time, insects are spotting the web and veering away." If the spider wants to grab a meal, they might sacrifice some safety for an easier catch.
And to see some fascinating webs, you can still head to the moviesor at least the DVD player. The webs that make up the opening sequence of the first Spider-Man film, Blackledge said, were spot-on. "They had such a great variety of webs," he said. "Somebody had really done their homework."
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