A hedgehog is any of a wide variety of small quilled mammals of the order Insectivora found through parts of Europe, Asia, Africa, and New Zealand. There are no hedgehogs native to the Americas.
Hedgehogs are easily distinguished by their quills, which are hollow hairs made stiff with keratin. Their quills are not poisonous or barbed and, unlike the quills of a porcupine, cannot easily be removed from the animal.
Hedgehogs are most closely related to gymnures, also to other insectivora such as moles, shrews, tenrecs and solenodons.
A hedgehog's primary defense is to roll into a tight ball, causing all of the quills to protrude outward. They also make loud huffing and popping noises. This is an effective defense against most predators. As a result, hedgehogs have few natural predators, primarily birds (especially owls), and ferrets. Wild hedgehogs are sometimes killed by humans, particularly by road vehicles.
Hedgehogs occasionally perform a ritual called 'anointing'. When they come across a new scent, they will lick and bite the source. They will then form a scented froth in their mouths and paste it on their quills with their tongue. It is rather amazing to see a hedgehog contort and lick the top of its head. This camouflages them with the new scent of the area and provides a possible poison or source of infection to any predator that gets poked by their quills.
Hedgehogs are primarily nocturnal and feed on snails, worms, and insects. In areas that have hedgehogs in the wild, they are often welcome as a natural form of garden pest control. Many people leave food out to attract hedgehogs. When doing so, keep in mind that hedgehogs are lactose intolerant, but will eagerly eat cheese products and drink milk, making them sick. Dog and cat food is a better food than dairy, but it is often too high in fat and too low in protein. It is best to leave out only a small treat, leaving them plenty of appetite for the pests in your garden.
Depending on the species, the gestation period is 40-58 days. The average litter is 3-4 newborns. Larger species of hedgehogs live 4-7 years in the wild (some have been recorded up to 16 years). Smaller species live 2-4 years (4-7 in captivity).
The European Hedgehog, Erinaceus europeaus, is a mammal of the order Insectivora, about 20cm in length.
Unlike the smaller, warmer climate species, the European Hedgehog may hibernate in the winter.
The Domesticated Hedgehog is a distant relative of the European Hedgehog. It is a cross-breed between the White-Bellied or Four-Toed Hedgehog (Atelerix albiventris) and the Algerian Hedgehog (A. algirus). It is smaller than the European Hedgehog, and thus is sometimes called African Pigmy Hedgehog.
Domesticated Hedgehogs may be kept as pets, whereas it is unwise to attempt to keep any other breed of hedgehog as a pet. They prefer a warmer climate (above 72 degrees Fahrenheit) and do not hibernate. Attempts to hibernate are commonly fatal.
It is illegal to own a hedgehog as a pet in many areas. Check with animal control before considering having a hedgehog as a pet.
Hedgehogs are a powerful form of pest control. A single hedgehog can keep an average garden pest free by eating up to 200 grams of insects each night. Therefore, it is common throughout England to see people attempting to lure hedgehogs into their yards with treats and hedgehog-sized holes in their fences.
One problem with using hedgehogs for garden pest control is the use of chemical insecticide. While the hedgehog is immune to most poisons, it is not immune to them when ingesting insects full of the poison. This causes many accidental hedgehog deaths in England as well as in the United States where pet hedgehogs eat contaminated bugs inside the house.
In areas where hedgehogs have been introduced, such as New Zealand and the islands of Scotland, the hedgehog itself has be come a pest. As with many introduced animals, it lacks natural predators. With overpopulation, it kills off more insects than initially intended and expands its diet to include things such as snails, worms, and the eggs of wading birds.
There are many diseases common to hedgehogs, mostly fatal. These include cancer, fatty liver disease, heart disease, and wobbly hedgehog syndrome.
Cancer is very common in hedgehogs. The most common is squamous cell carcinoma. Squamous cell spreads quickly from the bone to the organs in hedgehogs, unlike in humans. Surgery to remove the tumors is rare because it would result in removing too much bone structure.
Fatty liver disease is believed by many to be caused by bad diet. Hedgehogs will eagerly eat foods that are high in fat and sugar. Having a metabolism designed for low-fat, protein-rich insects, this leads to common problems of obesity. Fatty liver disease is one sign. Heart disease is another.
Wobbly hedgehog syndrome is very similar to multiple sclerosis in humans. The hedgehog slowly loses muscle control. Initially, it wobbles when attempting to stand still. Given time, the hedgehog loses all muscle control, including control of the lungs and heart. Vitamin E has been shown to delay the deterioration, but it is very temporary as a higher and higher dose is required.
The common American holiday Groundhog Day was started in ancient Rome as Hedgehog Day and is still celebrated as such through much of the world. There are no native hedgehogs in America, so the early settlers chose the groundhog as a substitute.
The hedgehog was originally referred to as an urchin, which gives rise to other terms, such as calling an offensive child an urchin and the common sea urchin.
The hedgehog was introduced to New Zealand in 1870 and caused immense damage to native species including insects, snails and ground-nesting birds, particularly shore birds.