How do you distinguish a millipede from a centipede – both multi-segmented arthropods that have a lot of legs? Although there are many less obvious differences, centipede bodies are relatively flexible and they have one pair of legs per body segment. Most of a millipede’s segments have two legs, and their tubular body is quite rigid.
Depending on the species, millipedes have between 80 and 750 legs, with most having fewer than 100, but they didn’t start out their lives with this way. When they hatch, millipedes only have three pairs of legs; every time they molt, they add more body segments and legs. When threatened, millipedes quickly coil their body into a spiral, protecting their legs and fragile underbody with their armor-like body plates (tergites).
If you come across a millipede, know that you’re looking at one of the earliest animals to breathe air and make the move from water to land. Pneumodesmus newmani, a fossil found in Scotland, dates back 428 million years and is the oldest fossil specimen with spiracles for breathing air.
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We don’t often see millipedes because of their preference for secluded, moist sites where they feed on decaying vegetation and other organic matter. Compost piles, heavily mulched shrub or flower beds, rotting logs, or the soil under logs and stones are likely spots to find these arthropods. Millipedes overwinter as adults, and have been seen migrating in the fall, presumably in search of overwintering sites that will provide them with some protection.