Millipedes are bizarre in a dozen different ways, but they don’t bite and curl up when threatened

The word millipede comes from the Latin mille, meaning “thousand,” and pes, meaning “foot.” Despite the name, most millepedes do not have 1,000 feet; however, in August 2020 a biologist in Western Australia discovered a millipede that has 1,306 legs. Until this time, scientists knew of no millipedes with more than 750.

Biologists found the 1,306-legged millipede 200 feet below ground. It is threadlike and lacks eyes and pigmentation. The brown surface-dwelling millipedes that you and I usually encounter are much different.

Millipedes have existed for more than 400 million years. They were one of the first organisms to walk on land. Some prehistoric fossils indicate that 300 million years ago, millipedes were 6 feet long! As oxygen levels in the atmosphere decreased over time, millipedes (and other creatures) became smaller.

Today, there are about 80,000 species of millipedes in 140 families. They are small: one-16th of an inch (2 mm) to 4 inches long. Most have fewer than 100 pairs of legs. They have a hard exoskeleton and a segmented body. Most are black or brown.

You will most often encounter millipedes on forest floors where they eat and break down dead plant and animal matter. Millipedes are neither carnivores nor herbivores. They are classified as dentrivores, which means they eat detritus, also known as decomposing organic matter, such as rotting wood, poop, leaf litter and decaying fruit. Their droppings recycle nutrients back into the soil at a faster rate than would occur through decomposition alone. That makes them an important part of the ecosystem.

Millipedes require moisture to live, so they are found in damp places. Besides forest floors, you might encounter one in your basement or bathtub, mulch or compost. Inside a home, millipedes usually die within a day or two because the moisture level is not high enough to sustain them.

How can you tell a millipede from a centipede? If the critter has one pair of legs per body segment, runs very fast and bites, it is a centipede. If it has two pairs of legs per body segment, moves slowly, and does not try to bite, it is a millipede – they do not have mouth parts for biting or stinging. When threatened, millipedes curl up into a ball exposing their hard outer skeleton, protecting their legs and soft underside.

Some millipedes can secrete a fluid through holes in the side of the body that can repel insect predators and stain human hands. Although millipede secretions are not usually harmful to humans, they can burn ants and insect predators. Some primates, such as Venezuelan capuchin monkeys and lemurs, have learned to irritate millipedes and rub the secretions on their fur to repel mosquitoes during the rainy season.

Millipedes breathe through two pairs of openings in their exoskeleton near the base of their legs. Each opening connects to a system of breathing tubes. Millipedes have a heart that runs the entire length of their body.

Millipedes overwinter in debris and sheltered areas under rocks or boards. In most species, the males have modified legs called gonopods, usually on their seventh segment, that transfer sperm to the female. There are a few species of millipedes that reproduce asexually, but this is not the norm. Because gonopods come in many shapes and sizes, they are the primary method scientists use to determine a millipede species.

In the spring, the female lays eggs in a protected area, most from 20 to 30 eggs. The American millipede – the most common in Massachusetts – lays only one egg in a nest of regurgitated leaves and poop. She coils herself around her egg and nest until the egg hatches in a few weeks. After the egg hatches, the hatchling goes off alone. The mother’s work is done.

Another common Massachusetts millipede is the greenhouse millipede (Oxidus gracilis). These are originally from Japan but have been introduced around the world through the transport of garden soil and mulch. As you might have guessed, they are common in greenhouses. Greenhouse millipedes are about an inch long and are somewhat bumpy. They do not have eyes; they get around using their antennae. They can also retain a bubble of air in their breathing holes, allowing them to stay underwater for a great deal of time. They live four to seven years.

Young millipede hatchlings may be legless, but molt into a form with six segments and three pairs of legs. As they continue to molt, millipedes add segments and pairs of legs. Because each molt can take a few weeks, and millipedes are especially vulnerable to predators while molting, millipedes hide in their burrows during this period. After molting, they are unable to use their legs until their exoskeleton hardens. While they are waiting, they eat their old exoskeleton, which contains valuable nutrients. Millipedes molt every four to 12 months. They reach adulthood in two to five years but may continue to grow and molt even after reaching adulthood.

Millipedes are adapted for burrowing. Their legs are attached in the center of their body rather than along the edges. A millipede picks up a grain of dirt with its mouth and passes the dirt back along its body segments to the end of its body. Using this process, a millipede digs out a burrow in moist soil, where it is protected from drying out. When millipedes are not eating, they are usually in their burrows. Millipedes come out at night when they are less likely to dry out. For this reason, we may not see them that often.

Have you taken photos of our urban wild things? Send your images to Cambridge Day and we may use them as part of a future feature. Include the photographer’s name and the general location where the photo was taken.

Jeanine Farley is an educational writer who has lived in the Boston area for more than 30 years. She enjoys taking photos of our urban wild things.

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