So, I think a lot of people know that ‘milli’ means thousand and ‘centi’ means hundred, which implies that millipedes have a thousand legs and centipedes have one hundred. That’s not exactly true of course but it is true that both have an unprecedented amount of legs and millipedes have more than centipedes.
Both Centipedes and Millipedes belong to the group Myriapoda and they both have so many legs because way back in their evolution a mutation copied the body segment making gene. Basically you have the same body segment over and over again because of a duplication error.
I know you’re thinking, ‘that’s interesting and all but give me some practical information, how can I tell these two apart?’ Fair question, you can’t exactly count all the legs to identify one of these critters. You can count the legs on each body segment however, which is quite easy. Centipedes it turns out have one pair of legs per body segment and millipedes have two pairs of legs per body segment. That means a total of two legs per body segment for centipedes and four legs per body segment for millipedes. There’s also a definite difference in the overall look of the animals. Millipedes have a more stream-lined look to them, almost as if they were little snakes and centipedes have bigger, blockier body segments. Why should you care about this unless you’re a zoologist, naturalist or just a natural history nerd? There is one very practical reason you should care: Centipedes are venomous carnivores and millipedes are peaceful detritivores. Centipede bites are usually just painful but they’re also something you want to avoid. Or if you’re like me, perhaps some day you’ll find yourself on a biology expedition in a cave near the grand canyon hand catching a new species of centipede and you should know the danger you’re in. Or perhaps you’ll be stranded in the jungle and need to find food, it’d be handy to gobble down a giant millipede but I’d avoid those painful centipedes, a bite inside your mouth isn’t good.