Hedgehog

The hedgehog is a small, spiny mammal belonging to the subfamily Erinaceinae, within the family Erinaceidae. Seventeen species exist across five genera, native to parts of Europe, Asia, and Africa, and introduced to New Zealand. No hedgehogs are native to Australia or the Americas today, though the extinct genus *Amphechinus* once lived in North America. Their distant relatives include shrews, with gymnures possibly as an intermediate link, and they have remained largely unchanged for 15 million years. Like many mammals, they are nocturnal. Their spines resemble those of porcupines (rodents) and echidnas (monotremes), but are not barbed, poisonous, or easily detached. Young hedgehogs shed their baby spines in a process called quilling, and adults may also lose spines due to illness or extreme stress. When threatened, they roll into a tight ball, tucking in their face, feet, and belly, using two large back muscles to direct the quills. Lightweight desert species with fewer spines may flee or ram an intruder instead. Hedgehogs are mostly nocturnal, sleeping under bushes, grass, rocks, or in underground dens. All wild hedgehogs can hibernate, with duration depending on temperature, species, and food supply. They are vocal animals, making grunts, snuffles, and squeals. They also perform anointing: upon encountering a new scent, they lick and bite it, produce a scented froth, and spread it on their spines. This may camouflage them or infect predators. Hedgehogs have some immunity to snake venom via the protein erinacin, though a viper bite can still be fatal. They are one of four mammal groups (along with pigs, honey badgers, and mongooses) with a mutation in the nicotinic acetylcholine receptor that blocks α-neurotoxin. Their sense of smell is poorly studied, but tests show similar olfactory electrical activity to cats.

Hedgehogs are omnivorous, eating insects, snails, frogs, toads, snakes, bird eggs, carrion, mushrooms, grass roots, berries, melons, and even cat food. Afghan hedgehogs eat berries in early spring after hibernation. During hibernation, their body temperature drops from 30–35°C (86–95°F) to 2–5°C (36–41°F). Gestation lasts 35–58 days, with litters of three to four for larger species and five to six for smaller ones. Adult males sometimes kill newborn males. Lifespan is relatively long for their size: in captivity, eight to ten years; in the wild, larger species live four to seven years (some up to 16), and smaller species two to four years (four to seven in captivity). Newborn hoglets are blind, with quills covered by a protective membrane that dries, shrinks, and falls off after cleaning. Predators include birds (especially owls), ferrets, foxes, wolves, and mongooses. In Britain, the European badger is a key predator in intensively farmed areas, and hedgehog rescue societies avoid releasing hedgehogs into badger territories. Badgers also compete for food. Hedgehogs are sensitive and easily stressed by humans, which can be fatal. Wildlife clinics recommend keeping captured hedgehogs in a dark, ventilated box with minimal noise and handling.

The name "hedgehog" dates to around 1450, from Middle English *heyghoge*—*heyg* (hedge) for its hedgerow habitat, and *hoge* (hog) for its piglike snout. Other names include urchin and hedgepig. Their spines are hollow hairs stiffened with keratin, usually brown with pale tips. Leucistic "blonde" hedgehogs occur on the Channel Island of Alderney. The most common pet species are hybrids of the white-bellied (or four-toed) hedgehog (*Atelerix albiventris*) and the North African hedgehog (*A. algirus*).