A hedgehog is a spiny mammal of the subfamily Erinaceinae, in the eulipotyphlan family Erinaceidae. There are 17 species of hedgehog in five genera found throughout parts of Europe, Asia, and Africa, and in New Zealand by introduction. There are no hedgehogs native to Australia and no living species native to the Americas. However, the extinct genus Amphechinus was once present in North America. 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. Like many mammals, they have adapted to a nocturnal way of life. Their spiny protection resembles that of porcupines, which are rodents, and echidnas, a type of monotreme. Hedgehogs are commonly brought to wildlife clinics in Europe. They are sensitive and easily stressed by humans, which can sometimes be fatal. Therefore, when hedgehogs are captured for treatment, clinics recommend keeping them in a dark, ventilated box with minimal noise and avoiding frequent handling or other interactions.
Etymology 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. Other names that are used are urchin and hedgepig.
Description Hedgehogs are easily recognized by their spines, which are hollow hairs made stiff with keratin. Their spines are not poisonous or barbed and, unlike the quills of a porcupine, do not easily detach from their bodies. However, the immature animal's spines normally fall out as they are replaced with adult spines. This is called "quilling". Spines can also shed when the animal is diseased or under extreme stress. Hedgehogs are usually brown, with pale tips to the spines, though leucistic 'blonde' hedgehogs are found on the Channel Island of Alderney.
Hedgehogs roll into a tight spiny ball when threatened, tucking in the furry face, feet, and belly. The hedgehog's back contains two large muscles that direct the quills. Some light-weight desert hedgehog species with fewer spines are more likely to flee or attack, ramming an intruder with the spines, rolling up only as a last resort. Hedgehogs are primarily nocturnal, with some species also active during the day. Hedgehogs sleep for a large portion of the day under bushes, grasses, rocks, or most commonly in dens dug underground. All wild hedgehogs can hibernate, though the duration depends on temperature, species, and abundance of food. Hedgehogs are fairly vocal, with a variety of grunts, snuffles and/or squeals. They occasionally perform a ritual called anointing. When the animal encounters a new scent, it will lick and bite the source, then form a scented froth in its mouth and paste it on its spines with its tongue. 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. Anointing is sometimes also called anting after a similar behavior in birds. 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. In addition, hedgehogs are one of four known mammalian groups with natural protection against another snake venom, α-neurotoxin. 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. The sense of smell has been little studied in the hedgehog, as the olfactory part of the mammal brain is obscured inside the neopallium. Tests have suggested that hedgehogs share the same olfactory electrical activity as cats.
Diet Although traditionally classified in the abandoned order Insectivora, hedgehogs are omnivorous. They feed on insects, snails, frogs and toads, snakes, bird eggs, carrion, mushrooms, grass roots, berries, and melons. Afghan hedgehogs devour berries in early spring after hibernation. Hedgehogs have been observed eating cat food left outdoors for pets.
Hibernation When a hedgehog hibernates, its normal 30–35 °C (86–95 °F) body temperature decreases to 2–5 °C (36–41 °F).
Reproduction and lifespan Hedgehog gestation lasts 35–58 days, depending on species. The average litter is three to four newborns for larger species and five to six for smaller ones. As with many animals, it is not unusual for an adult male hedgehog to kill newborn males. Hedgehogs have a relatively long lifespan for their size. In captivity, lack of predators and controlled diet contribute to a lifespan of eight to ten years depending on size. In the wild, larger species live four to seven years (some recorded up to 16 years), and smaller species live two to four years (four to seven in captivity). This compares to a mouse at two years and a large rat at three to five years. Newborn hoglets are blind, with their quills covered by a protective membrane which dries and shrinks over several hours, and falls off after cleaning, allowing the quills to emerge.
Predators The various species have many predators: while forest hedgehogs are prey primarily to birds (especially owls) and ferrets, smaller species like the long-eared hedgehog are prey to foxes, wolves, and mongooses. Hedgehog bones have been found in the pellets of the Eurasian eagle owl. In Britain, a predator in intensively farmed areas is the European badger with populations lower in areas with many badgers. Some hedgehog rescue societies will not release hedgehogs into known badger territories. Badgers also compete with hedgehogs for food.
Domestication
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