Spider Sense: Fast Facts on Extreme Arachnids
for National Geographic News
|June 23, 2004|
With more than 37,000 described species, spidersfrom the tiny
armored spider to the Goliath birdeater tarantulacruise 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 threadsor 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 commonand what distinguishes them from insectsare four pairs of legs and no antennae.
The spider world has its own Goliaththe 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 reclusehave 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'sa 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.
Spiders eat spiders. Females sometimes eat their mates, even while they are mating. Some spiders specialize in hunting down other species of spider and have evolved ways to grab them, even when their victims are in the center of their strongholdstheir webs.
Spiders are hunted as much as they are hunters. Birds, lizards, snakes, scorpions, and other spiders all prey on spiders. Some insects also hunt down spiders, including the mantis and a wasp that specializes in catching and paralyzing spiders. The wasp buries the spider alive, so that its young can feed on fresh food when they hatch.
Most spiders have eight eyes. Some have no eyes and others have as many as 12 eyes. Most can detect only between light and dark, while others have well-developed vision. Experiments have demonstrated that some spiders can recognize and respond to specific shapes on television monitors. However they're equipped to see, all spiders have highly evolved systems to detect prey and danger.
Some cultures have found ways to use a spider's trap to get their own meals. In the South Pacific native people have made fishing nets from a spider's silk. People encourage nephila spiders to build webs between two bamboo stakes, which are then used for angling.
A spider eats about 2,000 insects a year, so spiders are good to have around the home. The reward for the trouble? All too often, a smack with a newspaper. Spiders are usually killed by people because the arachnids seem scary, not because they're dangerous.
If you are bitten by a spider, the California Poison Control Center recommends keeping the wound clean and treating the symptoms that follow. If the bite becomes infected or does not heal, see a physician.
Some cultures chomp down on spiders as a delicacy and have been doing so for hundreds of years. In the South Pacific people have eaten the same spiders they use to weave fishing netswith some diners saying the cooked spiders taste nutty and sticky like peanut butter. In spots in Southeast Asia, street vendors sell fried spiders to passersby.
According to urban legend, the daddy longlegsthose gangly creatures that seem to hang from corners around the houseare poisonous, but have mouths too small to bite humans. The name "daddy longlegs" is used in several countries to refer to a few different speciesincluding harvestmen, which aren't actually spiders and have no venomand spiders in the family Pholcidae, which are not known to have venom that affects humans.
Pesticides won't successfully knock out spiders. The highly mobile eight-legged animals will come back to an area that's been sprayed because, unlike insects, they're not strongly affected by residual pesticides. To prevent spiders from coming inside the house, arachnologists suggest sealing off any cracks or gaps where spiders can slip in. But to control insects that can cause damage to your propertysuch as termiteswhy not let their natural predators, spiders, inside to do the work?
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