How does a hedgehog roll up?

Pretty much every time that we pick up the hedgehog animal ambassador, she rolls into a ball.

Her pointy spines stand erect, and you can't see any other part of her.

(See a video of Honey the hedgehog here.)

The reason that hedgehogs do this is the same reason that turtles will pull their appendages into their shells --- protection.

When they are frightened, or annoyed, hedgehogs will roll into a ball so that an predator will feel the full brunt of its sharp spines and will then leave the hedgehog alone.

You wouldn't want to eat something that pokey would you?

opens IMAGE file But how does a hedgehog do it? If you and I tried to roll into a ball, you could still see our arms and legs. However, when Honey the hedgehog rolls up, you can't see anything but spines!

When threatened, a hedgehog contracts two muscles that pull in opposite directions. Think about pulling a drawstring bag, when you pull the strings in different directions, the opening of the bag closes up. When the hedgehog contracts its muscles, they pull on the ball-like base of its spine, and that spine is pulled from a relaxed position to standing straight up.

The muscles pull different spines in different directions, so they crisscross and form a nearly impenetrable barrier.

Then its belly and back muscles help it tuck its head, legs and tail inside extra skin.

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This hedgehog has a condition that caused it to lose its spines, but it gives a glimpse into how it uses muscles and extra skin to roll into a protective ball.
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Fun facts about hedgehog spines

• Hedgehogs can climb but struggle to get back down. Sometimes they will simply roll into a ball and drop, allowing the spines to cushion the fall. Wild hedgehogs have been seen dropping from up to 20 feet this way.
• Hedgehogs can add extra protection to their spines by licking poisonous plants that they're immune to and then making a frothy saliva in their mouths. They then lick their spines, spreading the plant's poison, to become even more irritating to predators.
• After birth, hedgehog spines are short and soft. They will harden, and then they will lose their spines as they age and grow a new set of spines for their adults bodies.