Other than a skunk, what animal in the woods would you least want your dog (if you own one) to meet in a close encounter? First hint: it’s a rodent. Second hint: it’s a big, prickly rodent.

Yes, it’s a North American porcupine (Erethizon dorsatum), sometimes called a quill pig. Porcupines move slowly, and like skunks, are not likely to run away from you. If you spot a porcupine, you could probably watch it for quite a while as it peacefully goes about its business. Most of us know better than to get too close, but dogs often aren’t so wise.

The porcupine’s quills keep this animal safe from almost all predators and also make it dangerous for a dog to try to play with or attack. A porcupine is covered with about 30,000 quills, which are 3-4 inches long and very sharp. Only its face and underside lack quills. Porcupines are nearsighted but hear and smell well.

If a porcupine feels threatened, its quills will stand up – much as our own body hair might “stand on end” when we have a fright – and it will turn its back to the threat and thrash its quill-covered tail. The porcupine’s quills are only loosely attached to its skin, so if they touch an animal, they stick in readily and detach easily from the porcupine. Contrary to what some people think, a porcupine can’t throw or shoot its quills at another animal.

Surprisingly, a porcupine’s skin contains an antibiotic, which may help to prevent infection when quills come out, or when a porcupine gets stuck with its own or another’s quills. The quills are actually modified hairs. They are white and black, with black tips.

The quills go into flesh easily in one direction but are hard to pull out in the reverse direction. That’s because the tips are covered with microscopic flat plates that overlap like roof shingles. The quill tips slide smoothly in, but the bottom edges of their shingle-like plates push against flesh and grip when the quill is pulled out.

The quills also tend to work their way deeper into an animal’s flesh, at a rate of about an inch a day, causing pain and further injury, especially if one hits a vital organ. If a dog gets quills stuck into its face or mouth, a veterinarian will probably need to sedate the dog in order to remove them.

Our prickly porcupines lead solitary lives, but autumn and winter are a bit of an exception. The porcupine mating season is September – December, so male and females seek each other out then. (They flatten their quills during courtship and mating.) Porcupines don’t hibernate, but several may hole up together in a winter den in a hollow tree or rock pile.

On a winter day, you might be surprised to spot a porcupine resting in a leafless tree. What’s it doing up there? Porcupines climb well, and they find safety up a tree, as well as twigs and buds to eat. They’re usually most active at night, like so many other animals.

Look for porcupines, or signs of them, near stands of hemlock trees – a favorite winter food. They eat the green needles, as well as twigs and bark. You might find piles of small, stripped branches on the ground under a hemlock. During summer they eat a wide variety of vegetation, including green plants, twigs, acorns, seeds, and roots.

Porcupines also have an appetite for salt, sometimes venturing onto roads where they can become road kill. In some cases a porcupine might get salt by gnawing on a sweaty object such as a wooden canoe paddle, ax handle, or leather goods.

After developing for 7 months, baby porcupines are born in the spring, April to June. A female gives birth to just one. A newborn porcupine weighs a full pound, has its eyes open, and is covered with short, soft quills that quickly harden. The young porcupine nurses for about 3 months.

In New England today, only one predator can reliably take a porcupine – the fisher (Martes pennant – see Nature Notes 193). This member of the weasel family is active and quick enough to dart in, repeatedly attacking a porcupine’s face and eventually flipping the porcupine over to get at its unprotected underside. In the 1950s, after fishers had been absent for many decades, Vermont’s porcupine population was growing unchecked and damaging timber resources by eating bark. Fishers were re-introduced in Vermont to control the porcupine population. This ecological strategy worked, and a balance was restored by the 1970s. Native Americans hunted porcupines for meat and also used the quills to decorate clothing, moccasins, leather bags, baskets, and other items. The art of quillwork pre-dated beadwork. One way they gathered quills was to throw a blanket over a porcupine and then collect the quills that were stuck in the blanket.

What about old-fashioned “quill pens”? They’re made from bird feathers, not porcupine quills.

Where did porcupines come from? Those in North America have been here long enough to be considered native. They moved up from South American after the land bridge (in Panama) formed between North and South America 3 million years ago. Our porcupines may seem unusual to us, but their relatives include 28 other species of porcupine around the world.

People sometimes refer to porcupines as hedgehogs, but hedgehogs are a different group of animals. For example, the European hedgehog (Erinaceus europaeus) lives in Britain and northern Europe. It eats mainly insects and has spines that don’t detach. It’s also small – only 2-1/2 pounds and 10 inches long – especially compared to our porcupines, which are sizeable, at an average of 20 pounds and 1-1/2 - 2 feet long plus a 6 -12 inch tail.

In the human world of politics, the porcupine is sometimes used as a mascot for the Libertarian party, much as the elephant and the donkey are used as mascots for the Republican and Democratic parties, respectively.

If you spot a real porcupine this winter, consider it a treat!