Porcupines are a type of rodent found in two main regions of the world, so scientists group them into either Old World or New World porcupines. Old World porcupines live in Europe, Africa, and Asia; some examples are the North African crested porcupine, African brush-tailed porcupine, and Indian crested porcupine. New World porcupines live in North, Central, and South America; some examples are the Canadian porcupine, Mexican hairy dwarf porcupine, and Brazilian porcupine.

All porcupines are nocturnal and quite adaptable, found in a variety of habitats, as long as there is vegetation. There are a few differences between the Old World and New World species:

Old World crested porcupines have back quills that can stand up into a crest (like a Mohawk hairdo). The crest starts from the top of the head and goes down to the shoulders. They display their weaponry for all to see. Each quill is marked with black and white bands. Some quills can be up to 20 inches (51 centimeters) long. These long, pliable quills act as guard hairs and form a "skirt." When threatened, the skirt can be erected, making the porcupine appear two to three times bigger.

Smaller, rigid quills that are 8 inches (20 centimeters) long are densely packed over the Old World porcupine’s rump and back. These can stab any potential threat. At the base of the tail, the porcupine has blunt, hollow quills that rattle when shaken, serving as a warning to potential predators. If the noise doesn't work, the porcupine may try to charge backward into the predator. When threatened, a crested porcupine stamps its feet, growls, and grunts to scare off the predator.

The quills of New World porcupines are much smaller (about 4 inches or 10 centimeters long) but work just as well. The end of each quill has a small barb (like a fish hook) that snags the flesh, keeping the quill stuck in the enemy's skin. Any animal with a quill lodged in its skin will have a hard time removing it if it doesn't have fingers and thumbs! When threatened, New World porcupines erect quills that jut out in various directions, like a pincushion. The porcupines may stand still in a defensive pose, or they may charge the enemy. New World porcupines are also known to lash out at predators by batting at them with their quill-laden tails. During fights, New World porcupines also chatter their teeth to sound fierce.

Porcupines cannot shoot their quills! Quills are just modified hairs made out of keratin, the same substance found in our own hair and fingernails. The quills do not cover the underside of the porcupine. Porcupines have muscles at the base of each quill that allow them to stand up when the animal is excited or alarmed. Like all hairs, quills do shed, and when the porcupine shakes, loose quills can fly off (but without deadly force). Still, the quills can cause problems, and puncture wounds inflicted by porcupines are serious.

Having quills does not mean that the porcupine's life is trouble free. Large cats, especially lions, and human hunters (bushmeat trade) threaten Old World porcupines. New World porcupines’ predators include martens, wolverines, pythons, eagles, and great-horned owls. One porcupine predator, the fisher, is able to flip the North American porcupine onto its back, exposing its unprotected belly. In fact, the fisher has been reintroduced to some areas of North America in hopes of bringing destructive porcupine populations under control.

There are still many myths and misunderstandings about porcupines, just as there were in ancient times. The philosopher Aristotle warned of the dangers of getting too close to a porcupine: the quilled beast could "shoot its deadly needlelike darts" over great distances at hunters and dogs alike. After reading this far, you know that is not true!