A female millipede lays eggs inside a nest underground where they undergo an incomplete metamorphosis. Once the eggs hatch, the baby millipedes remain in the nest until they molt at least once. The millipedes gain new body segments each time they molt until reaching adulthood in 2 to 5 years.
Although the name millipede means thousand legs, they don't really have a thousand legs. Millipedes have two pairs of legs per body segment and single pairs on the first three segments of their body located on their thorax. Although it's rare, some millipedes have four legs on each body segment. Even though each millipede has a different number of body segments, their legs typically number less than 100 in total. Their legs are short and designed to push their bodies through soil and vegetable litter. Their legs also always remain in line with their body.
Millipedes curl into tight balls, spiral into the ground, or emit poisonous or foul-smelling substances through their skin when they're threatened. The substances that some millipedes release often burn or sting, and in some cases, they temporarily discolor the skin. Some brightly colored millipedes release cyanide compounds from their skin, and large tropical millipedes shoot a noxious compound across several feet to blind their attackers.