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Why do spiders spin silk?

Spitting spiderSpitting spiderSpiders, scorpions and mites are not insects but arachnids. Insects have three pairs of legs and three body sections, while arachnids have four pairs of legs and two body sections. They also have two grasping “limbs” called pedipalps. Spiders have many pairs of eyes. All spiders can produce silk, but only some kinds use it for spinning sticky webs to trap flying insects.

Close-up of the head of a jumping spiderClose-up of the head of a jumping spider

A spider pulling silk from its spinneretsA spider pulling silk from its spinnerets

Spider silk

A spider makes silk from a liquid produced by glands inside its abdomen. As the silk is drawn out of the spider’s body through the spinnerets, it becomes a solid thread. The spider pulls the silk out using the claws on its back legs. Besides making webs, spiders use their silk to wrap up their prey when captured, to cocoon their eggs, as a safety line, and even as a parachute to float in the wind.

Spider silk is as strong as steel thread of the same thickness, but much lighter and bendier.

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