There are 17 species of hedgehog in five genera found throughout parts of Europe, Asia, and Africa, and in New Zealand by introduction.

Hedgehogs share distant ancestry with shrews (family Soricidae), with gymnures possibly being the intermediate link, and they have changed little over the last 15 million years.

The name hedgehog came into use around the year 1450, derived from the Middle English heyghoge, from heyg, hegge 'hedge', because it frequents hedgerows, and hoge, hogge 'hog', from its piglike snout.

Hedgehogs roll into a tight spiny ball when threatened, tucking in the furry face, feet, and belly.

Hedgehogs sleep for a large portion of the day under bushes, grasses, rocks, or most commonly in dens dug underground.

Some experts believe this might serve to camouflage the hedgehog with the local scent, and might also lead to infection of predators poked by the spines.

Like opossums, mice, and moles, hedgehogs have some natural immunity against some snake venom through the protein erinacin in their muscles, though in such small amounts that a viper bite may still be fatal.

Developing independently, pigs, honey badgers, mongooses, and hedgehogs all have mutations in the nicotinic acetylcholine receptor that prevent the binding of the snake venom α-neurotoxin.

[10] The sense of smell has been little studied in the hedgehog, as the olfactory part of the mammal brain is obscured inside the neopallium.

They feed on insects, snails, frogs and toads, snakes, bird eggs, carrion, mushrooms, grass roots, berries, and melons.

In captivity, lack of predators and controlled diet contribute to a lifespan of eight to ten years depending on size.

As of 2019[update], it is illegal to own a hedgehog as a pet in the US states of Hawaii, Georgia, Pennsylvania, and California,[20] as well as in New York City, Washington, D.C. and some Canadian municipalities.

Attempts to eliminate hedgehogs from bird colonies on the Scottish islands of North Uist and Benbecula in the Outer Hebrides were met with international protest.

Hedgehogs will eagerly eat foods high in fat and sugar, despite a metabolism adapted for low-fat, protein-rich insects.

Hedgehogs are also highly susceptible to pneumonia, with difficulty breathing and nasal discharge,[26] caused by the bacterium Bordetella bronchiseptica.

[28] Hedgehogs can suffer from balloon syndrome, a rare condition in which gas is trapped under the skin from injury or infection, causing the animal to inflate.

[29] In 2017, the BBC reported a case of a male hedgehog "almost twice its natural size, literally blown up like a beach ball with incredibly taut skin".

[30][31] At Stapeley's Wildlife Hospital, vet Bev Panto, said, "I have seen three or four of these cases and they are very strange every time and quite shocking ...

They were eaten in Ancient Egypt and some recipes of the Late Middle Ages call for hedgehog meat.