Believe it or not, hedgehogs have been around for at least 15 million years (to put that in perspective, modern humans have only been around for about 200,000 years) and have changed very little in that time! There are 16 different species of hedgehog, spanning 5 genera, which are found natively throughout Europe, Asia and Africa (introduced hedgehogs are also present in New Zealand). The species found in Britain is Erinaceus europeaus and it tends to live among woodlands, hedgerows, scrub and cultivated land. They are also commonly found in human-modified environments like gardens and parks.
In the wild, hedgehogs have a life span of about 5 years, though they can live as long as 8 years in captivity. The Western European hedgehog, E. europeaus, has four toes on each back foot and five on each front foot to help them forage and burrow. Their legs are surprisingly long, hidden underneath their loose skin, and allow them to reach speeds of up to 9 kilometres per hour. Hedgehogs are roughly between 15 and 30 centimetres in length and weigh between 700 and 1000 grams, though some can weigh up to 2 kilograms.
Hedgehogs are most readily identifiable by the 5000 to 7000 individual spines—which are actually stiff, hollow hairs—covering their body, with which they defend themselves. In response to perceived threats, the hedgehog will pull loose folds of skin over its head, and curl into a spine-covered ball using drawstring-like muscles to protect its face and underside. At the base of each spine, below the skin, the spine-end rounds into a ball. This allows the spines to bend and prevents them from impaling the hedgehog upon impact. Each spine typically lasts about a year before being shed and replaced (though not all at once) in a process called quilling.
Fun fact: Hedgehogs sometimes covers their prickles in foamy saliva. This is called self-anointing. The reasons for this peculiar behaviour are largely unknown, though it often occurs after exposure to particular odours or tastes.