Jack Choo of Opoho School asks :-

I have been observing slaters in my garden. Why do slaters and centipedes have so many legs?

Otto Hyink, an entomologist at Otago Museum, responded.

Both these bugs have many legs because of their general body shape. These body shapes have evolved over a very long period of time (many millions of years). Just like our bodies have evolved for us to be able to walk on two legs the body shapes of slaters and centipedes give them certain advantages, which help them thrive in their environments.

Slaters are crustaceans (related to crabs, shrimp, lobsters etc) that have adapted to living on the land. They have retained a general body structure common to all crustaceans. Slaters have three body parts, a head, thorax and abdomen. The thorax is made up of seven segments, each of which has a pair of legs (14 legs in total). The segments are covered with overlapping plates, which offer some protection from predators and help retain moisture. Having numerous overlapping plates gives them more flexibility than being covered by a single plate. It is possible that this is why they have evolved to have so many body segments and, therefore, so many legs.

Centipedes have long thin bodies made up of many segments with each segment having a pair of legs. Centipedes only live in fairly damp places such as the leaf litter in your garden. This is because their long flat bodies do not retain moisture very well. This body shape obviously gives them some real advantages in their environment because they thrive despite all the competition from other bugs such as insects and spiders. It is possible that their long, thin bodies help them get into tight spaces to hunt their prey, which is more difficult for bugs with shorter, fatter body.