• Small Spiders, Big Mysteries
    Orb spider venom is not dangerous to people.

    Photograph by Matjaz Kuntner

    Silky Smooth
    Spider silk is the toughest material we know from nature, Dr. Ingi Agnarsson says. It is stronger than steel of the same width, and it can stretch much farther.

    The combination of strength and stretchiness makes it a very attractive material for humans because there are many possible ways we could use it. Hospitals and doctors could use it to stitch up patients and make artificial body parts that need to bend a lot. It also could be used to make protective clothing for police officers, air bags for cars, fishing nets, and parachutes.

    But it is difficult to get enough spider silk to use for anything, Dr. Agnarsson said. The silk material we make clothes from comes from moth larvae, which make a lot more silk than spiders do. People have tried to make spider silk in labs, but it is not as strong as the silk spiders make themselves.

    "There is something that the spider does that we don't understand that is responsible for the strength," he said.

    The silk of Madagascar spiders is stronger even than other spider silk. "We think this has something to do with crossing the rivers," Dr. Agnarsson said. The webs are exposed to wind and birds and have to hold up for a long time, he added, so they need to be extra strong and very stretchy.

    By Evelyn Kent

    Friday, January 21, 2011

    There are spider webs in the highland rain forest of Madagascar that are so huge, they make you wonder if the creatures that built them are big enough to have a starring role in a horror movie.

    How huge? Big enough to wrap around a VW Beetle, that's how huge. But instead of being the size of the giant spiders in the Harry Potter books, they're more like the spiders in Harry's cupboard under the stairs—a little on the big side, but nothing out of the ordinary.

    "They are no bigger than some of the spiders you can find in gardens in America or Europe," said Dr. Ingi Agnarsson, a biologist. He and his research partner, Dr. Matjaz Kuntner, believe the webs are made by several closely related spider species. All these species are smaller than the thumb of an adult human being.

    These are orb spiders, which make large, round webs that look a lot like the ones people decorate with at Halloween. First, the spider will spin a silk thread between two objects, like tree branches. This is called a bridge line. The spider makes the bridge line stronger by traveling back and forth along the line, adding more silk to it. Then it adds a line that will help anchor the web to the ground or another object. It continues adding anchor lines until the web looks like a bicycle wheel with spokes.

    These spiders, all of which are in the genus Caerostris, have not yet been fully studied by scientists and exist only on the island of Madagascar. Dr. Kuntner and Dr. Agnarsson plan to travel there in February to study them extensively.

    The biologists do know two more things—besides size—that make these spiders extraordinary: They build their webs over running water, such as streams and rivers, and the silk they use to make their webs is stronger than that of other spiders.

    The two facts are probably related, Dr. Kuntner said. Web-building spiders tend to use a lot of energy to make their webs, and orb spiders have to make bigger webs than most. The silk would have to be strong to hold up for long enough for the spider to catch food.

    An orb spider’s entire web is large, but the bridge line is especially enormous. Those can reach up to 14 meters (45 feet), stretching across flowing rivers and streams. The spiders have no obvious way to get their bridge lines across the rivers and streams.

    "We have no idea how they make these webs," said Dr. Kuntner.

    How might they get those silk threads across the river? Biologists have many theories.

    Do they send out a thread to float across the river and entangle in a tree on the other side? Probably not, said Dr. Agnarsson. The distance is too far, and it is likely that the thread would break and fall into the river.

    Do they crawl across another spider's bridge line? Probably not, because some spider would have had to make the first bridge line across the river.

    Do they put on a teeny pair of goggles, grab a leaf, point it in the right direction and wait for the right wind? Probably not, no matter how much fun that may sound.

    The scientists are going to Madagascar to study these spiders to find out. They will have a team of people to watch the spider webs day and night to see if the spiders show up to build or repair webs. They may even damage some of the webs to see if a spider comes out to fix them.

    One of the big questions the scientists want to answer is if the spiders' prey is as extraordinary in size as their webs are. It seems reasonable to wonder if a big web is meant to catch a big dinner. If it is, what do they do with it once it is caught?

    The biologists will also collect some spiders to study back home in their labs. Dr. Agnarsson works at the University of Puerto Rico. Dr. Kuntner works at the Slovenian Academy of Sciences and Arts.

  • Term Part of Speech Definition Encyclopedic Entry
    anchor Verb

    to hold firmly in place.

    anchor line Noun

    thread strung from a spider's web to the ground or another object.

    artificial Adjective

    created by people and industry.

    biologist Noun

    scientist who studies living organisms.

    bridge line Noun

    thread strung between two objects in a spider's web.

    enormous Adjective

    very large.

    entangle Noun

    to tangle or twist together.

    extensive Adjective

    very large.

    extraordinary Adjective

    unusual or uncommon.

    Halloween Noun

    night of October 31, celebrated by children dressing in costume and going to neighbors for candy.

    Harry Potter Noun

    series of books (named after the main character) by J.K. Rowling.

    island Noun

    body of land surrounded by water.

    Encyclopedic Entry: island
    larva Noun

    a new or immature insect or other type of invertebrate.

    moth Noun

    flying insect.

    orb spider Noun

    spider that makes a wheel-shaped web.

    parachute Noun

    device which allows a person to glide down safely from a great elevation.

    rain forest Noun

    area of tall evergreen trees and a high amount of rainfall.

    reasonable Adjective

    logical.

    silk Noun

    soft, strong fiber spun by some moth larvae, spiders, and other animals.

    spider Noun

    eight-legged animal (arachnid) that usually spins webs to catch food.

    spider web Noun

    structure made from thin, sticky material spun by spiders and originating from their bodies.

    spoke Noun

    straight rod coming from the center of a wheel (hub) and supporting its rim.

    steel Noun

    metal made of the elements iron and carbon.

    stream Noun

    body of flowing water.

    Encyclopedic Entry: stream
    theory Noun

    explanation that has not been proven as fact.

    VW Beetle Noun

    small car introduced by Volkswagon (VW) in 1938.

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