Hedgehogs are any of the species belonging to the taxonomic subfamily Erinaceinae. They are small land mammals that can easily be recognized by the thousands of prickly spines that cover their back. They eat mostly insects but will also consume bird eggs, lizards, and even venomous snakes. Their habitat is varied, as some species live in deserts while others thrive in rainforests. Their name comes partly from the grunting noises they make that sound similar to a pig's snort. They give live birth to up to two litters a year, and will hibernate during the coldest parts of the year (some desert species will estivate). Some odd behaviors are their mating rituals in which they circle one another for hours and a process called "self-anointing" where the hedgehogs nibble on a foreign substance and lick it over their spines. Although loved in area such as the United Kingdom, their introduction into non-native areas has caused some controversy between hedgehog conservationists and those that do not want the creatures to push out their native species.
Hedgehogs range in size from six to fifteen inches and in weight from one to three pounds with males usually being slightly larger than females.    They possess the general mammal systems such as a respiratory system with lungs and a circulation system with a four-chambered heart.  They have a long backbone, short legs, and thirty-six to forty-four teeth.   Most have five toes and small nails on their front paws while having only four toes with long claws that grow continuously on their back paws.  Most have poor eyesight, however, other senses compensate for this weak sense. Although on most species the ears are small, hedgehogs’ hearing is acute. Their long snouts aid in smelling, another keen sense in the creature, and also in detecting nearby threats. 
Hedgehogs’ fur ranges in color from white to brown to even black.  Their spines are simply a modified type of fur made of tough keratin.  Hedgehogs can have up to 7,000 of these sharp spines.  The spines are hollow, which provides lightness while preserving the strength. They are not barbed like the quills of the porcupine and are not poisonous. These sharp spikes cannot be ejected from the skin over even pried loose easily unless the hedgehog is young or very sick.  While the hedgehog wanders around, these spines provide protection for its back. However, to protect its soft-furred underbelly it curls up into a tight ball. In order to provide complete protection, the hedgehog uses long circular muscles that are found along the sides of its body from its rump to its neck. By contracting these muscles, the skin pulls around the creature and the spines form a complete spiny coat around the rolled up hedgehog. 
Hedgehogs do not mate for life.  The mating season for European hedgehogs begins in spring or sometimes as early as September, while African hedgehogs breed year round.   When a male and female hedgehog meet in the wild, they will circle one another for up to an hour, during which time the female assumes a flattened posture so that her spines will not harm the male. After mating the male usually leaves, and the female must raise the young by herself.  The gestation period is thirty-four to thirty-seven days, and the female gives birth to between one and seven pups. However, about twenty percent of baby hedgehogs will never leave the nest. The pups are born blind and bald, but their preliminary spines soon begin to emerge through the skin.   These small spines will eventually be shed and adult spines will grow during a process called “quilling.” Their eyes open in ten days, and by one month they are accompanying their mother on foraging trips.  They are independent at seven weeks.  Although up to two litters can be produced each year, the second litter may not survive if they do not have enough to time grow and put on body weight before winter hibernation. 
Most European and some northern African hedgehogs enter hibernation when the weather becomes cold or if there is an extreme lack of food.  To prepare for hibernation during cold spells, the hedgehog gains much weight in the autumn months to store up fat. They usually enter hibernation around November, but may still be wandering around up until Christmas, especially if they have been unable to acquire enough body weight to sustain themselves through their hibernation.   Once they are safe inside their burrows, nests, or some other structure like a shed or wood pile, they begin the process of hibernation.   The hedgehog essentially enters a state of suspended animation. They cease to move, their breathing slows, and their internal blood and organ chemistry may alter slightly to avoid consuming too much of their stored fats.  Their heart rate also slows from 190 to twenty beats a minute.  To awake, the hedgehog metabolizes enough fat to bring its circulation and temperature up to normal standards. This can take anywhere from one half to a full hour, but the hedgehog may speed up the process by shivering. The hedgehog may awake during their hibernation due to a warmer period that returns their temperature and heart rate to normal or because they need to forage for more food. Also, a waterlogged nest can disturb a hibernating hedgehog.  Some desert species undergo a similar process called estivation in which they become dormant during the hottest parts of the year. 
The approximate fourteen species of hedgehogs live in diverse climates from deserts to rainforests to gardens. They are native to the continents of Asia, Europe, and Africa. They are mostly nocturnal and will forage for food at night. While mostly insectivorous, they also feed on snails, slugs, worms, and some also eat berries, bird eggs, lizards, frogs, melons, carrion (dead animals), and mushrooms.  Some even feed on small rodents.  Hedgehogs can even consume poisonous snakes. However, they are not completely immune to the toxins, and therefore cannot sustain a direct bite from a snake.  However, for those species who can find them, hedgehogs prefer slugs and worms.  While foraging for food, they will produce grunting noises like those of a pig. This behavior is part of the reason for their name.  Hedgehogs typically nest in dry areas and make nests from moss and leaves. When away from their safe nests, they employ several defense mechanisms. When approached by a predator such as foxes, stoats, pine martens, and primarily badgers, all hedgehogs can roll up into a tight ball.  Some young hedgehogs will jump into the air, poking their spines into the face of their adversary to remind them that they make a very uncomfortable snack. 
Their prickly spines can become even more irritating when hedgehogs perform an odd process called "self-anointing." Hedgehogs chew a substance and then distribute frothy saliva over their spines. They may chew and anoint substance such as leather or dog feces, but they may also chew toxic substances. Why exactly hedgehogs anoint is still a mystery. Some theorize that when they encounter a new substance in their environment, they anoint themselves with it to camouflage their scent. Others think it is a more offensive tactic that wards off predators because of the toxic spines or a bad scent. A study in 1977 showed that anointed spines are more irritating than clean spines. Volunteers pricked themselves with anointed and clean spines, and their reports showed that the spines with the toxic toad skin saliva on them were more painful than clean spines. 
Hedgehog population numbers fall in the United Kingdom, a place where it is met with love and adoration. In 1532 when Henry VIII ruled, the king placed a bounty on vermin. Over half a million bounties were collected on hedgehogs in the seventeenth and eighteenth centuries since they were seen as pests at the time. While they are no longer hunted, hedgehog numbers still decline in the UK.  The People's Trust for Endangered Species estimates that 36 million hedgehogs lived in the UK in the 1950s, 2 million could be found in the 1990s, and that now only 1 million hedgehogs survive in the UK. Habitat loss and extreme weather change are likely potential factors in this decline.  Although hedgehogs can survive well in backyard gardens, hazards are still present. Lawnmowers or strimmers can seriously injure hedgehogs who are nesting or foraging in the grass. Hedgehogs can fall into holes with no way out or even become trapped in netting. Some also nest in old bonfire pits and can be killed if the fire is lit again. Pesticides are also a suspected hog killer. This may be because the insecticides kill off hedgehog prey, or because hedgehogs are consuming poisoned insects. Just like humans, hedgehogs have to get from one place to another, and this means crossing man-made roads. Hedgehog roadkill has become a common sight on roads in the UK. Even something as simple as a McFlurry® cup can be a danger to a hedgehog. Once they push their heads into the lid to lick up the sugary liquid inside they cannot pull their heads out. Because of this, McDonalds released a hedgehog-friendly cup in 2006. Other steps such as making hedgehog cruelty illegal are being taken to protect these creatures. 
While in the UK hedgehogs are no longer considered pests, other countries and areas are beginning to remember why they were once considered vermin. Hedgehogs were introduced to the Hebrides Islands off of Scotland to cull the garden slug population there. Because they had no natural predators on the island, their numbers grew quickly. Because of their diet of not only insects but also bird eggs, they have damaged rare ground-nesting wading birds' populations by consuming their eggs. This destruction of bird eggs is so dramatic that a study found that when the birds nested in areas without hedgehogs, they were two times as likely to nest successfully. Conflict exists between those that want to protect hedgehogs, such as the UK, and those in areas like the Hebrides Islands that have been invaded by them. New Zealand experiences similar problems due to the introduction of hedgehogs in the 1800s. Here they damage bird, lizard, and weta populations. During the breeding season, females tend to consume even more of these species than other times of the year. Conservationists of native New Zealand species have grown concerned about the hedgehog's growing numbers.
Basic facts about hedgehogs:
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- Vaughan, Adam. Hedgehog population in dramatic decline The Guardian. Web. Published 29 January 2013.