The hedgehog has changed very little in the last 15 million years. It had already established itself before the arrival of woolly mammoths and rhinos. Its unspecialised skeleton is very similar to that of the early mammals of 50 million years ago, but still serves the hedgehog perfectly well. The main different between the hedgehog and other mammals is the shortness of its neck, even though it consists of the usual seven vertebrae, as in human beings.
The hedgehog is Britain's only mammal with a spiny coat. It is a common sight in the countryside and gardens near dawn and dusk. Sadly, it is also seen as a corpse on the road. An adult hedgehog has up to 5000 yellow-tipped spines. However, the fur on its underside is soft. It may grow up to 30 centimetres long and has an average weight of 400 grams (it can weigh up to 2 kilograms, especially in autumn). This length includes a tail which is about 4 or 5 centimetres long.
The hedgehog's spines are its main distinguishing feature. At one end they taper to a sharp point, at the other end the spine bends into a 'neck' and forms a rounded bulb which is buried in the skin. When a hedgehog senses danger, it erects the previously flat spines so they point in all directions. The spines in this position provide very effective protection against its predators, so good that it has very few natural enemies. The bulb end of the spine is a valuable defence because if the hedgehog falls heavily or suffers a blow, the springy spines absorb much of the shock and the rounded end does not cause injury as it is pushed against the body. The spines themselves are hollow tubes covered in ridges, so providing the strength with the minimum of weight. Rather than a seasonal moult, the spines are grown, shed and replaced continuously. A spine may last more than 18 months before it falls out and is replaced by a new one.
Hedgehogs don't often make noises and the ones that they do cannot normally be detected by the human ear. Babies in the nest, for example, make a high-pitch twittering. Non-vocal sounds include quiet snufflings made while a hedgehog is hunting for food and the 'huffing' noise often heard during fights. Hedgehogs produce this sound by sharply breathing out through their nostrils. Courtship is accompanied by loud and aggressive snorting. The most alarming sound is the occasional loud scream made by a hedgehog in distress.
A baby hedgehog has white spines which are gradually replaced with brown and cream banded ones. Occasionally the new spines are white too, giving a blonde hedgehog with black eyes. They are quite common in the Channel Islands, but are found rarely elsewhere. True albino hedgehogs, with pink noses and eyes are quite rare. Although other mammal species produces the occasional all-black individual, black hedgehogs are completely unknown. Bald hedgehogs occasionally occur, but they are unlikely to survive as they are very vulnerable without their spiny protection.