There are more than 37,000 species of spiders in the world. In general, spiders pose very little risk to humans. Only about 25 species are believed to have venom that can harm people. Their venom is used mostly to paralyze prey. Each spider eats an average of 2,000 insects per year. They use their ability to jump to hunt down prey, and then pounce on it. Some spiders can jump as much as 50 times their body length. If a human had similar ability, he could jump 90 meters.
Not only can spiders jump far, but they can also walk upside down on smooth surfaces. Their feet are covered with tiny hairs that enable them to hold 170 times their body weight before coming unstuck. That is equivalent to a children’s super-hero carrying 170 people from danger while clinging to the side of a building with his fingers and toes.
Spiders can also spin as many as seven different kinds of silk. Some of the silk is so strong that it rivals the strength of steel. Spiders use the silk for many different purposes, such as catching insects in webs and then wrapping them up so that they cannot escape. They also use silk to travel from place to place and to form egg sacs.
Spiders come in a wide variety of sizes. The largest known spider is the Goliath bird eater tarantula. This South American spider can be as big as a dinner plate. The smallest known spider is the mygalomorph spider from Borneo. Its body is the size of a pinhead.
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