When the cold season comes and food becomes scarce, hedgehogs curl up into a ball and hibernate until spring, slowing down their heart rate and breathing to consume as little energy as possible. Hedgehogs are generally nocturnal and feed exclusively on insects. To protect themselves they have a layer of about 6,000 quills, which however are not poisonous nor do they come off easily like those of the porcupine — which is a completely unrelated species.