Millipedes are arthropods, not insects—they’re also invertebrates. They have an cylindrical exoskeleton and eat decomposing plant matter. Centipedes, on the other hand, are carnivores. Millipedes aren’t harmful to humans; they can’t bite and they’re not venomous. However, some species excrete a chemical as a defense mechanism that can irritate skin.
Millipedes are most active at night. They break down dead plants and leaves as they move through the material. They mostly eat particles of decaying wood and other plant material. Sometimes, millipedes that can’t find enough moisture in the soil begin feeding on living plants to access water.
Millipedes molt many times, growing longer each time they shed that old part of their exoskeleton. These arthropods then eat the skin they’ve molted so they don’t waste any nutrients.
A female millipede can lay up to 100 eggs at a time, hiding them in the ground or in a burrow. In a few weeks, the eggs hatch into young millipedes with few segments. The lifespan of a millipede depends on its environment and ranges from a few months to five or more years.
Though millipedes are not harmful to humans and can sometimes be beneficial to gardens, they become a nuisance pest when large numbers start living around or entering the home. These pests need shelter to lay eggs and survive the winter. The first sign of an infestation is usually seeing the millipedes, as they don’t affect human food or fabric like other pests.