Web-slinging and wall-crawling come naturally to these bug hunters
Darrell Ubick bends over a square of canvas, picking carefully through oak leaves, dried moss, and bark pieces. An itsy-bitsy spider tries to sneak away, but Mr. Ubick spots its tiny, ghostly-green body. This particular spider is found only in oak trees along the California coast.
"As a kid," says Mr. Ubick, "I always liked spiders and insects." By sucking on one end of a tube draped around his neck, he plucks the miniature spider off the canvas. "There is a mesh inside the tube," he explains, "so I never get a spider down my throat. He gently blows the spider into a glass vial.
The first thing to know about spiders is that they are not insects. Insects have six legs, spiders have eight. Unlike most insects, spiders don't have wings or antennae. Like scorpions, mites, and ticks, spiders are "arachnids" (uh-RAK-nids). This group of creatures gets its name from Arachne (uh-RAK-nee), a beautiful Greek maiden. According to legend, Arachne made the mistake of beating the goddess Minerva in a weaving competition. In revenge, Minerva turned Arachne into a web-weaving spider.
Scientists have named 40,000 kinds of spiders. (There are only about 4,000 kinds of mammals.) At the California Academy of Sciences in San Francisco, where Darrell Ubick works, 9 million insects and spiders are preserved in trays and glass vials.
"Scientists would love to identify all the different types of spiders," Ubick says. He has discovered about 30 new spider species himself. "But it will take a long time. We probably only know about half of all species, and even California has many spiders we don't know much about."
Spiders are nature's bug hunters. "Carnivore" makes us think of wolves and tigers, but spiders are probably the most common carnivores on land.
Just as lions and eagles hunt in different ways, so do different types of spiders. Crab spiders lie in wait, ambushing their prey with a lightning-fast strike. Jumping spiders stalk their prey like a cat. They can jump 20 times their body length to pounce on an insect. Sometimes a jumping spider will anchor itself by a strand of silk, and launch itself into space after a flying insect just like a bungee-jumper. The spitting spider stuns its prey by shooting it with a nasty glob of venom and silk.
Although most spiders hunt insects, a few spiders, such as tarantulas, are big enough to eat frogs, lizards, and even small birds. A few diving spiders capture tiny fish.
Spiders kill their victims with venom (poison). Then the spider pumps special juices inside, turning its prey to liquid. "They suck up their prey like a milkshake," Darrell says. "Have you ever taken an orange, rolled it around, mashed it up, then stuck a straw in to get the juice? That's how a spider eats."
Many spiders spin webs to snare their meals. Different spider species make many kinds of webs round "orb" webs, funnel-shaped webs, sheet webs, and even underwater webs. The teeny-tiny green spider that Ubick collected spins a small, flat web on an oak leaf.
All spiders spin silk, though not all spiders make webs. Spiders that don't make webs use their silk to line their nests and cover their egg sacs.
Spiders spin silk from special "spinnerets" on their tail end. A spider has many different "faucets" on each spinneret, to spin different kinds of silk. Have you ever wondered how a spider keeps from being stuck in its own web? A spider can spin both sticky and nonsticky silk. When it walks on its own web, it walks on the nonsticky strands. Even if a spider becomes stuck, it can eat its own silk. After a spider climbs up a line of silk, it may pull it up and snack on it!
Spider silk can also carry special "perfume." "Female spiders release chemicals with their silk," Ubick says. "If a male spider touches the silk, he knows it's a female of his species. So he follows the silken strand." Courtship is tricky among bug hunters, however. Female spiders are often bigger and stronger than males. In many spider species, males have special hooks on their legs to push the female spider's fangs back, just in case she is thinking of dinner instead of love.
Spiders don't have wings, but their silk helps many spiders become frequent fliers. "They release a line of silk," Ubick says, "and it can be picked up by the wind like a kite. Lots of smaller spiders can take advantage of air currents and be transported hundreds or thousands of miles." (Don't worry about flying tarantulas, though. They're too heavy.)
The tiny green spider that Ubick studies has relatives in Europe and Asia. Could its distant ancestors have flown to California from far away?
Modern chemists and engineers haven't invented anything to equal spider silk. Pound for pound, spider silk is stronger than steel, more elastic than nylon, and harder to break than rubber.
Spider silk also lasts a long time. Only harsh acids can break it down. That's why you find so many abandoned webs in dark, forgotten places.
Spiders aren't the only creatures that use spider silk. Many birds use it in making nests. People in New Guinea once encouraged large spiders to spin webs in hoops made of bamboo. When the spider was done, the spider web was used as a fishing net!
Most spiders have eight eyes as well as eight legs. Even with all those eyes, most spiders don't see very well. Instead, they use their legs the way we use our tongue, ears, and fingertips. Spiders have special hairs on their legs that let them "taste" their food. Other hairs let them "hear" tiny movements in the air or feel small movements on their webs.
How do spiders crawl up walls? They have two or three claws and dozens of little hairs on each foot. The hairs are wet, but not sticky. "Just like a little scrap of paper will stick to a wet fingertip," Ubick says, "the spider can stick to a wall with these moist hairs."
But even to a spider scientist like Ubick, spiders are still a mystery. How are spider species related to each other? How many kinds are there? How do they "see" the world? How might we adapt spider silk for human uses?
Spiders may give some people the creeps, but nature has given them a special talent. Charlotte, an orb-weaving spider in E.B. White's "Charlotte's Web" (1952), said it best: "I don't know how the first spider in the early days of the world happened to think up this fancy idea of spinning a web, but she did, and it was clever of her, too. And since then, all of us spiders have had to work the same trick. It's not a bad pitch, on the whole."
In the 'Spider-Man' movie, the Peter Parker character uses some real spider tricks:
Like a real-life spitting spider, Spider-Man shoots a glob of icky goo on his adversaries.
In the scene where Spider-Man starts to crawl up the side of a building, a close-up shows spiky hairs shooting out of his fingers. Real spiders have these hairs, which help them climb walls.
Spider-Man uses his spider webbing as a safety line, a trapeze, and a way to wrap up the bad guys (his "prey"). Real spiders use silk this way, too!
Spider-Man supposedly gets his talents from a "mutant" spider that combines the genes of three spider species. No single spider has all of "Spidey's" talents web-spinning, jumping, and spitting.
In the movie, we never see what happens to all the webbing Spider-Man uses. A real spider would eat most of it.
And finally: In the movie, Spider-Man's webs shoot out of his wrists. If he were a real spider the webbing would shoot out of a spinneret on his behind.