After cats, hedgehogs might be the internet's favorite animal. But how much do you know about these spiky mammals—other than how cute they look when getting a bath?

1. A GROUP OF HEDGEHOGS IS CALLED AN "ARRAY."

Hedgehogs poking around in the dirt.
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But it doesn't come up much, since hedgehogs are solitary creatures who usually come together only to mate.

2. HEDGEHOGS ARE ILLEGAL IN SOME PARTS OF THE UNITED STATES.

Hedgehog in a bucket with purple beads.
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The hedgie has gained some popularity as a pet—but some cities and states still qualify them as wild animals, which are not allowed to be kept domestically. These include Arizona, California, Georgia, Hawaii, Pennsylvania, and New York City and Washington, D.C. In some areas, like Maine, you need permits in order to own one.

3. A HEDGEHOG HAS BETWEEN 5000 AND 7000 QUILLS.

Hedgehog in a garden.
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Muscles along the animal's back can raise and lower the quills to respond to threatening situations.

4. THERE ARE 17 DIFFERENT SPECIES OF HEDGEHOG, NONE OF WHICH ARE NATIVE TO AMERICA.

Two African hedgehogs.
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Australia also has no indigenous hedgehogs; the hedgies in New Zealand were introduced by humans.

5. HEDGEHOGS RELY ON HEARING AND SMELL BECAUSE THEY HAVE VERY POOR EYESIGHT.

Hedgehog looking for strawberries.
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And even their limited sight is best in the dark as an adaption to their nocturnal lifestyle.

6. UNLIKE PORCUPINE QUILLS, HEDGEHOG SPIKES ARE NOT BARBED, AND THEY'RE NOT POISONOUS.

A close-up of hedgehog quills.
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The inside of the quills are mostly hollow, with a series of complex air chambers that make them light but strong.

7. HEDGEHOGS GOT THEIR NAME FROM THEIR PREFERRED HABITAT—GARDEN HEDGES—AND THE PIG-LIKE GRUNTS THEY MAKE.

Hedgehog playing in purple flowers.
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Their taste for destructive insects makes them a historically welcome presence in English gardens.

8. HEDGEHOGS CAN HIBERNATE, BUT NOT ALL DO.

A hedgehog rolled up in a little ball on some leaves.
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Which makes them one of only three mammals in Great Britain that hibernate (the other two being bats and dormice).

9. HEDGEHOGS ARE LARGELY IMMUNE TO SNAKE VENOM.

Baby hedgehogs nursing on their mother.
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This means that, although their typical diet consists of insects and berries, they can take down a viper in a fight and eat it, too.

10. THE SEA URCHIN IS ACTUALLY NAMED AFTER THE HEDGEHOG.

A baby hedgehog lying in a human hand.
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Before the more adorable name came into use, the spiky mammals were called "urchins" throughout the Middle Ages, and thus inspired the name of the similarly spiky sea creatures. Baby hedgehogs are still called urchins.

11. MEDIEVAL BESTIARIES AND ILLUMINATED TEXTS SHOW HEDGEHOGS GATHERING FOOD WITH THEIR QUILLS.

Hedgehog with two cherries stuck on his quills.
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This is inaccurate. But affinity for the image has persisted.

12. IN THE PRECURSOR TO GROUNDHOG DAY, HEDGEHOGS WERE THE SUPPOSEDLY PORTENTOUS CRITTERS.

Hedgehog curled up on some pine branches.
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But when German settlers got to America and found no hedgehogs, they turned to the similar-enough groundhog for their winter-weather predictions.

13. IN NEW ZEALAND, A SATIRICAL POLITICAL PARTY TRIED TO GET A HEDGEHOG ELECTED TO PARLIAMENT.

Little hedgehog walking in fall leaves.
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The McGillicuddy Serious Party was unsuccessful with their tiny candidate.

14. THERE USED TO BE SUCH A THING AS THE INTERNATIONAL HEDGEHOG OLYMPIC GAMES (IHOG).

Hedgehog swimming in a pool.
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Events included sprints, hurdles, and floor exercises.

15. ONE OF THE LESSER-KNOWN BROTHERS GRIMM FAIRY TALES IS CALLED HANS-MY-HEDGEHOG, ABOUT A BOY WHO IS BORN HALF HEDGEHOG.

Two hedgehogs cuddled in the grass.
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Not your style? Try another Grimm tale, The Hare and The Hedgehog.

16. WHEN EXPOSED TO PUNGENT SMELLS OR TASTES, HEDGEHOGS EXHIBIT A BEHAVIOR CALLED "SELF-ANOINTING," IN WHICH THEY RUB FROTHY SALIVA ON THEIR QUILLS.

Hedgehog sleeping with a leg out.
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The purpose of this behavior is unknown.

A version of this list first ran in 2016.