A group of porcupines is called a prickle.

The North American porcupine has about 30,000 quills. These quills are actually stiff hairs made of keratin. This is the same material found in human fingernails. The quills are loosely attached to the porcupine's skin so they pull off easily when a predator touches them.Each quill has tiny backward-facing barbs at the tip. Dr. Jeffrey Karp and other researchers found these barbs act like fishhooks. They make the quills four times harder to pull out of skin than a smooth needle. This helps the porcupine stay safe from larger animals like mountain lions.Porcupines sometimes accidentally poke themselves with their own quills. To prevent sickness, their quills are coated in special fatty acids. These acids act as a natural medicine to stop infections. This allows the porcupine to survive its own sharp defense system.Porcupines are the second-largest rodents in North America. Only the beaver is larger. While they spend most of their time alone, they may share dens in cold places like Canada to share body heat. This group is then called a prickle.