Why do centipedes and millipedes have so many legs?

Centipedes and millipedes are arthropods belonging to a group known as Myriapoda, meaning ‘many legs’. Their bodies are long and thin and they exhibit metamerisation, which means that their bodies are divided into many segments. This is why they have so many legs, as each body segment has a set of legs attached to it. Each segment can move independently alongside the next, so when a centipede or millipede walks the legs move in an undulating wave. This is a very primitive body shape – these animals have a fossil record that dates back at least 428 million years. Despite their name, centipedes don’t have 100 legs because they always have an odd number of body segments, and each segment has a set of two legs.

Main image: Chris Wightman/flickr