Hedgehog spine. Coloured scanning electron micrograph (SEM) of a broken hedgehog spine (yellow). It is surrounded by hairs (brown). The spine is a modified hair made from the protein keratin. Its interior is hollow and crossed with transverse septa, making the spine strong but light. Adult hedgehogs have about 8000 spines, which are used to protect against predators. Magnification: x25 when printed at 10 centimetres wide.