They are only alike superficially. Hedgehogs are insectivores and porcupines are rodents. Hedgehogs eat worms and insects on the ground and porcupines (in North America) eat tree bark and buds in the high branches and will chew up and destroy tools and things you touch with sweaty hands since they crave salt, and love to gnaw. They will chew the wires and hoses under the hood in your car, so beware. Hedgehogs are not found in America, and are just harmless. Porcupines will also swat animals (like your pet dog) in the face with their tails, if they get close to them, and the quills burrow themselves in. A vet will have to painfully pull those barbed quills out or they will keep working further ways inwards, the dog may get a bad infection from them and die. Porcupines won't attack you but give them their space, to stay safe. They can also grow a good bit bigger than hedgehogs. Even bigger ones live in Africa.