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A hedgehog is any of the spiny mammals of the subfamily Erinaceinae, in the order Eulipotyphla. There are seventeen species of hedgehog in five genera, found through 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 (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 have changed little over the last 15 million years. Like many of the first mammals, they have adapted to a nocturnal way of life.〔(【引用サイトリンク】title=WildlifeTrust.org.uk )〕 Hedgehogs' spiny protection resembles that of the unrelated rodent porcupines and monotreme echidnas. The name ''hedgehog'' came into use around the mid 15th century (they were earlier known as ''igls''). "Hedge" refers to its usual habitat, the hedgerow, while "hog" refers to its piglike snout,〔Oxford English Dictionary, Online edition. Retrieved 13 July 2007.〕 and the snuffling noise it makes whilst foraging. Other names include ''urchin'', ''hedgepig'' and ''furze-pig''. The collective noun for a group of hedgehogs is ''array'' or ''prickle''. ==Physical 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. A defense that all species of hedgehogs possess is the ability to roll into a tight ball, causing all of the spines to point outwards.〔 Since the effectiveness of this strategy depends on the number of spines, some desert hedgehogs that evolved to carry less weight are more likely to flee or even attack, ramming an intruder with the spines; rolling into a spiny ball is for those species a last resort. The various species are prey to different 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. Hedgehogs are primarily nocturnal, though some species can also be active during the day. Hedgehogs sleep for a large portion of the day under bush, grass, or rock, or most often in dens dug in the ground, with varying habits among the species. All wild hedgehogs can hibernate, though not all do, depending on temperature, species, and abundance of food. The hedgehog's back contains two large muscles that control the position of the quills. The average hedgehog has about 5,000 to 6,500 quills that are strong on the outer surface but filled with air pockets on the inside. When the creature is rolled into a ball, the quills on the back protect the tucked head, feet, and belly, which are not quilled. This is the hedgehog's last but most successful form of defense. Hedgehogs are fairly vocal and communicate through a combination of grunts, snuffles and/or squeals, depending on species. Hedgehogs 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. The purpose of this habit is unknown, but some experts believe anointing camouflages the hedgehog with the new scent of the area and provides a possible poison or source of infection to predators poked by their spines. Anointing is sometimes also called anting because of a similar behavior in birds. Like opossums, mice, and moles, hedgehogs have some natural immunity against snake venom through the protein erinacin in the animal's muscular system, although it is only available in small amounts and a viper bite may still be fatal. In addition, hedgehogs are one of four known mammalian groups with mutations that protect against another snake venom, α-neurotoxin. Pigs, honey badgers, mongooses, and hedgehogs all have mutations in the nicotinic acetylcholine receptor that prevent the snake venom α-neurotoxin from binding, though those mutations developed separately and independently. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「hedgehog」の詳細全文を読む スポンサード リンク
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