All caught up in a spider's web

No spider has all of Spider-Man's skills, but look closely and you'll find some amazing arachnids.

Spider-Man swings between tall buildings, traps villains in his web, climbs up vertical walls, and even hangs upside down from the ceiling – just as a real spider does. So why do so many people love Spider-Man, but not like spiders?

Scientifically, spiders belong to the animal group arachnids. They have eight legs and are found throughout the world – about 37,000 species of them.

Real spiders are specialists. You won't find one spider that has all of Spider-Man's characteristics, but look closely and you will find some pretty amazing arachnids.

Movie spiders

In the movie, Spider-Man's abilities are a combination of the skills of three different spiders – jumping, strength, and precognition (an ability to do something almost before thinking).

These genes were mixed to produce a superspider. This spider lands on Peter Parker's hand and bites him, turning him into Spider-Man.

Steven Kutcher, arachnologist (spider specialist) and entomologist (insect specialist), has consulted on more than 80 movies, including "Spider-Man" 1 and 3. He says many of the story points are not real: "Things are done in movies to entertain."

For "Spider-Man," Mr. Kutcher supervised hand-painting in blue and red the cobweb spider that bit Peter Parker so it would match his costume. The other spiders in that scene also received the same special treatment. The spider didn't really jump from branch to branch but down. The spider pulling up the grasshopper was helped.

But, as Mr. Kutcher points out, "fiction always has an element of truth."

Some of his favorite spiders are the bolas spider, which mimics the scent of a female moth to trap a male and then swings a sticky ball of silk at it, and the ogre-faced spider. That one even sounds like a Spider-Man villain – it throws a woolly web over its prey.

Mr. Kutcher recently heard about the double-trapdoor spider. "This spider has made two trapdoors," he says. "If a wasp (the spider's enemy) gets in the top door, the spider runs down into a side door. The wasp comes in, looks around, doesn't find the spider and leaves."

Spider-Man uses his silk to make webs, which he can swing from or use to wrap up villains. Spiders use varying types of silk for different purposes. The silk is produced from spinnerets, tiny organs at the back on the spider. It comes out as liquid and hardens to make a solid silk thread.

"As it comes out, the liquid molecularly lines up to become a solid," says Patrick Schlemmer, staff entomologist at the San Francisco Zoo. "Most spiders make five or more different types of silk."

Orb weaver spiders spin webs of sticky silk on a nonsticky silk frame.

Tarantulas use silk tripwires to alert them when prey is near and another kind of silk to line their burrows.

The argiope spider's silk is ultraviolet. This zigzag-shaped web looks like a flower to insects. The golden orb weaver can choose which color to make her web – golden for sunlit places or white for the shade. The silk she uses is so strong it can trap small birds.

Many spiders have to remake their webs every day. "Over time it becomes less sticky," Mr. Kutcher says, But rebuilding the entire thing takes a great deal of energy, so a spider will repair a web to save energy and then rebuild when it has to. Spiders recycle – they eat the old silk and then reproduce it to make a new web.

In the past, people used spider silk for centering cross hairs in measuring instruments by surveyors and in telescopic gun sights for soldiers.

Today, Polynesian fishermen use the silk of the golden orb weaver to make their fishing lines. And some people in New Guinea (an island in the East Indies) use webs as hats to protect themselves from the rain.

Dragline silk – tough, nonsticky silk used to create the frame of a web – is, pound for pound, stronger than steel. Some spider silk is so elastic it can stretch as much as 40 percent – almost half its size again – without breaking.

In fact, spider silk is so strong, elastic, and tough that scientists are trying to find ways to duplicate it. Imagine: bulletproof vests and bicycle helmets made of artificial spider silk.

Super senses

Spiders may have as many as eight eyes, but they don't always see very well. For example, "tarantulas see almost nothing; they mostly see things as shadows," says Marty Buxton, curator of natural history at Lindsay Wildlife Museum in Walnut Creek, Calif. "They feel their way along."

Tarantulas do not have a precognitive sense, but they are very sensitive to vibrations, Ms. Buxton explains. "They sit in their hole waiting for their silk tripwire to send a vibration. [Then] they react really quickly."

Some tarantulas move faster than others. The Indian ornamental tarantula is one of the fastest. Bigger than a hand span, this tree dweller makes a silken hide and lies in wait for its prey.

At the San Francisco Zoo, Mr. Schlemmer opens a tank and gently lifts a piece of wood that an Indian ornamental sits on. The tarantula zips around, pausing just a moment for a close-up photo.

The Costa Rican zebra tarantula doesn't move around much at all, Mr. Schlemmer says, "It can go for months without eating anything." He feeds it one cricket a week, the same diet as his black widow spiders.

When Mr. Schlemmer places a Mexican red-knee tarantula in my hands, it's surprisingly light and barely moves.

I can lift its legs and touch the tips of its claws, which are as soft as leather. Because of their gentle nature and striking coloration, these tarantulas make popular pets.

Those sold as pets are bred in the US now, because, Mr. Schlemmer says, "In the 1980s, it was overcollected in Mexico, so now it is protected."

The jumping spider can jump as much as Spider-Man does. Less than an inch long, they can leap up to 40 times their own length. That's comparable to you jumping 160 feet, the width of a football field!

When jumping spiders leap, they stay attached to a dragline of silk. If they fall, it acts as their safety line – much like a mountain climber's safety rope.

Jumping spiders have amazing eyesight, Mr. Schlemmer says, "They are one of the few spiders that you can see following you around with their eyes."

Jumping spiders have four pairs of eyes, which are arranged in a way that gives them 360-degree vision. They can even home in on things, much like a zoom lens.

Spiders really are amazing. Next time you see a spider in your neighborhood, treat it with respect. "In reality, spiders are pretty super," Mr. Kutcher says. "They do such amazing things, it's mind-blowing." Just like Spider-Man.

Learn more about arachnids

• About 3,500 species of spiders live in the US and Canada.

• The Goliath bird-eating spider is the largest. It is a type of tarantula found in the forests of South America. Although it can be as big as a dinner plate, its bite is like a wasp sting, pretty harmless to humans. Some people even eat them!

• One of the smallest spiders is the Samoan moss spider. It's about the size of a pinhead.

• Spiders are an essential part of the food chain. They're a tasty meal for birds, lizards, wasps, and other creatures. Birds use spider silk for nests and people benefit from spiders' insect control, since they eat flies and mosquitoes as well as locusts and cockroaches.

• The Kauai wolf and spruce-fir moss spiders are both endangered species, possibly due to development – building roads, housing, and farms over their natural habitats. Air pollution may be an additional factor.

• The loss of habitat is accelerating so fast that many more spiders may soon become endangered, experts say. When a spider species dies out, it means another menu item lost to its predators and more insect problems for all of us.

To find out more about spiders, see these websites:

• San Francisco Zoo:

•World Almanac for Kids:

• Steven Kutcher:

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