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Erethizontidae
Coendou
Sphiggurus
Erethizon
Echinoprocta
Family Hystricidae
Atherurus
Hystrix
Thecurus
Trichys
The porcupine's chief defense is its quills, sharp spines distributed across the rodent's back, sides, legs, tail, and head. They may be as dense as 150 per square inch, giving one animal as many as 30,000 quills. Porcupines do not throw their quills; unfortunate attackers approach closely enough to be swatted by the tail or brush against the animal. Like the related ordinary hairs, porcupine quills grow back when they come out.
A porcupine can defend itself by hiding its bare face from an attacker and keeping its bare belly to the ground. It may swat its tail at an assailant. Fishers sometimes successfully attack porcupines by biting their faces. Quills are not poisoned, but animals may die from a porcupine encounter if the quills prevent eating.
Quills are sharp-pointed, fitted with microscopic barbs, and expand on contact with warm flesh. Muscle contractions in a quill victim work the quill deeper, as much as an inch per day unless quills are removed promptly.
Porcupines occupy a wide range of habitats in tropical and temperate parts of Asia, Italy, Africa and the Americas. Porcupines live in forests, deserts, and grassland. Some live in trees, others stay on the ground.
Porcupines in search of sodium sometimes encroach on areas inhabited by people and eat tool handles, clothes, and other items that have been coated in salty sweat.
A porcupine is any of 23 species of rodent belonging to the families Erethizontidae and Hystricidae. All defend themselves with sharp spines (which are actually modified hairs) rather like those of the hedgehogs, which are part of the order Insectivora and more closely related to shrews and moles than they are to the rodents, and the echidnas, which as monotremes are very distantly related indeed.
Porcupines vary in size considerably: Rothschild's Porcupine of South America weighs less than a kilogram; the African Porcupine can grow to well over 20 kilograms.
The two families of porcupines are quite different and although both belong to the Hystricognathi branch of the vast order Rodentia, they are not closely related.
The 11 Old World porcupines are almost exclusively terrestrial, tend to be fairly large, and have quills that are grouped in clusters. They separated from the other hystricognaths about 30 million years ago, much earlier than the New World porcupines.
The 12 New World porcupines are mostly smaller (although the North American Porcupine reaches about 85 cm in length and 18 kilograms), have their quills attached singly rather than grouped in clusters, and are excellent climbers, spending much of their time in trees. The New World porcupines developed their spines independently, and are more closely related to several other families of rodent than they are to the Old World porcupines.