Why don’t spiders bleed to death if they lose a leg?

Check out ‘Bob the Former Disabled Tarantula’ on Facebook. This pet (now renamed Bobbi after she was discovered to be female) lost seven legs during an escape attempt, only to regrow them at her next moult, a few months later.

She didn’t bleed to death because when spiders lose legs, they usually come off at ‘break points’ – joints which contain muscles that constrict to minimise blood loss. If a leg becomes amputated before the break point, the spider still sheds its leg but only after additional blood loss. This can be fatal.

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• Why are spiders scary?
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• Why don’t spiders get caught in their own web?