Ask a Naturalist: How do Millipedes Grow?

This article was written by Emily Bowers, Minneapolis Park and Recreation Board Naturalist at North Mississippi Regional Park

April showers bring May flowers, which for some folks means more time spent in the garden, preparing for the summer growing season. Quality plants start with healthy soil, and decomposers play a vital role in creating an ecosystem that provides plants with easy access to air, water and nutrients. Living at the Kroening Interpretive Center as an education ambassador is one such decomposer, a Giant American Millipede (narceus americanus) named Victory. When visitors take a closer look at Victory and her many legs, which move in an undulating, wave-like motion as she walks, the most frequently asked questions are about all those legs.

Millipedes look like they should be in a category alongside insects or worms, but in fact they’re arthropods. This means they are invertebrates that have an exoskeleton, segmented body and jointed appendages, which makes millipedes more closely related to crayfish, lobsters and shrimps. The distinguishing characteristic of millipede bodies is that nearly all of the rounded segments have two leg pairs. Most millipede hatchlings begin life with six body segments and only three leg-pairs. Although “millipede” means thousand feet, adult millipedes have anywhere from 30 to 350 pairs of legs depending on the species, and most millipedes have fewer than 100 “feet.”

Like all arthropods, millipedes can only grow through a process called molting, by which they shed their hard exoskeleton and replace it with a new, larger one. When it’s ready to molt, a millipede will dig down into the soil in order to protect itself in this vulnerable state as well as the sensitive new exoskeleton as it hardens. Millipedes grow by continually molting; revealing newly formed additional segments and legs each time they do so. This process of growth is called anamorphic development. On average, millipedes will reach their full size in two to five years, but the speed of growth and the number of segments added with each molt varies from species to species.

Millipedes are mostly harmless; they don’t bite and their only defense is to curl up, possibly secreting foul-smelling or even poisonous substances that might irritate skin. As slow moving burrowers that live in dark, damp places, more often than not millipedes are seldom seen. Since they are nocturnal, millipedes hide under leaf litter, rotting logs and rocks during the day and then come to the surface to feed at night.

Despite their elusive habits, millipedes play a large role in breaking down nature’s waste and in turn improve soil conditions. Millipedes are one of nature’s little recyclers. They belong to a group of macro-decomposers, called detritivores, alongside other small invertebrates, insects and earthworms. These creatures feed on dead plants and animals, and are responsible for much of the physical breakdown of materials in the decomposition process, making organic matter into more digestible forms for microorganisms such as bacteria and fungi. The millipedes’ midnight snacking recycles nutrients back into the soil at a much faster rate than plants and animals decomposing naturally.

You can promote the natural process of decomposition and nutrient cycling in your garden by creating an environment in which decomposers will thrive. Every ecosystem is made up of three groups of organisms: producers, consumers and decomposers, and since gardens are engineered ecosystems it’s important we give consideration to each group. Support decomposers and make natural processes work for you by choosing non-invasive and sustainable gardening methods. Adding organic matter such as compost and peat moss to garden soils will provide food sources for decomposers while also maintaining good drainage, increasing moisture retention and airflow. Protect topsoil and provide places for macro-decomposers to hide with cover crops or a thin layer of mulch and leave old growth over winter. Finally, avoid the use of chemicals unless there’s no alternative as this can harm the beneficial soil creatures you are trying to cultivate.

Minneapolis Park and Recreation Board program buildings remain closed to the public until further notice due to the impacts of COVID-19. The MPRB’s priority is the health and safety of our park visitors and our employees. The MPRB urges park users to follow park use guidelines:

  • Do not visit parks or trails if you feel sick.
  • Take social distancing seriously. Stay at least six feet apart from other park users not part of your household.
  • Wash your hands immediately before and after visiting a park.
  • Walk to local parks. Do not drive across the city or metro to visit popular park attractions.
  • Do not hang out at the park all day. Visit to walk, bike or roll, then return home.
  • No group activities with people from outside your household.

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