Spider Sense: Fast Facts on Extreme Arachnids

Cameron Walker
for National Geographic News
June 23, 2004

With more than 37,000 described species, spiders—from the tiny armored spider to the Goliath birdeater tarantula—cruise the Earth on eight legs. Get a glimpse of the spiders' world with the juicy bites below:

The ancient Greek poet Ovid spun the tale of a young woman named Arachne, who boasted that she could weave as well as the goddess Athena. After a weaving contest between mortal and goddess, Athena began beating Arachne, who tried to hang herself in fright. Athena turned the arrogant weaver into a spider, and Arachne and her descendants have since then been weavers that hang from threads—or so the story goes.

• "Arachnid" isn't just a highfalutin word for spider. Spiders are arachnids, but not all arachnids are spiders. Arachnids are members of a class of animals that includes spiders, scorpions, mites, and ticks. What they all have in common—and what distinguishes them from insects—are four pairs of legs and no antennae.

The spider world has its own Goliath—the Goliath birdeater tarantula (Theraphosa leblondi). Found in the coastal rain forests of northeastern South America, this spider can be as big as a dinner plate and has been known to snatch birds from their nests. The spider world's David? The smallest spider is a mygalomorph spider from Borneo. Its body is the size of a pinhead.

• A spider might give Superman, the Man of Steel, a run for his money. Some silk made by orb weaver spiders rivals the tensile strength of steel. It's been suggested that the silk would be more effective than Kevlar in bulletproof vests. One problem: corralling a group of territorial spiders to produce the tough stuff. In addition, each spider produces so little silk that it wouldn't be practical to become a spider farmer.

Almost all spiders carry venom, but its purpose is to stun or kill their insect prey, not to attack humans. Of the known spider species, only about 25 are thought to have venom that has an effect on humans. The two bestknown venomous spiders in the U.S.— the black widow and the brown recluse—have not been proven to have caused any deaths in more than two decades.

The brown recluse spider, Loxosceles reclusa, often gets a particularly bad rap. While its natural range is in the south-central United States, people all over the country blame bites on this species.

Australia's most notorious spider, the Sydney funnel-web spider, has not been known to cause any deaths since 1980. In this species, the male spider's venom is more toxic than the female's—a rarity among spiders.

Spiders produce seven kinds of silk, ranging from the sticky stuff to trap and wrap their prey to superstrong threads for support. Spiders also use their silk as parachutes and to shelter themselves and their young. The various types of silk are produced by different specialized silk glands and nozzles called spinnerets. No one spider is able to produce the full range of silk.

• Spiders have evolved numerous ways to catch their prey, which is mostly insects but can also be frogs, fish, lizards, snakes, and birds. Some spiders are masters of disguise, blending into their background so that they look like parts of a flower or a leaf. Others hide under "trapdoors," jumping out of their hiding places to snatch a passing meal. Still others can leap many times their body length, covering great distances to grab their prey.

Bolas spiders "fish" for moths by dangling a sticky strand of silk impregnated with a substance that is similar to the pheromone that moths use to attract mates. Some spiders can walk on the surface of water. Others live underwater.

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