The main difference between Centipedes and this Millipede is not just the number of legs, but the number of legs per body segment. Centipedes have just one pair of legs, whereas Millipedes have two pairs per segment. This higher density makes it look like they have many more legs, which is not always the case. Millipedes are Arthropods, but not Insects (ie they don't have six legs). They can often be found under loose bark and dead wood.