10 Fascinating Facts About Millipedes

Millipedes Do Not Have 1,000 Legs

The term millipede comes from two Latin words - mil, meaning thousand and ped meaning feet. Some people refer to these critters as "thousand leggers." But both names are misnomers because scientists have yet to find a millipede species with 1,000 legs. Most actually have less than 100 legs. The millipede that holds the record for most legs has a mere 750, far short of the thousand leg mark.

Millipedes Have 2 Pairs of Legs Per Body Segment

This trait, and not the total number of legs, is what separates the millipedes from the centipedes. Turn a millipede over, and you'll notice that almost all its body segments have two pairs of legs each. The first segment always lacks legs entirely, and segments two through four vary, depending on the species. By contrast, centipedes have just one pair of legs per segment.

Millipedes Only Have 3 Pairs of Legs When They Hatch

Millipedes undergo a process called anamorphic development. Each time a millipede molts, it adds more body segments and legs. A hatchling begins life with just 6 body segments and 3 pairs of legs, but by maturity may have dozens of segments and hundreds of legs. Because millipedes are vulnerable to predators when they molt, they usually do so in an underground chamber, where they are hidden and protected.

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Millipedes, Class Diplopoda

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Millipedes Coil Their Bodies Into a Spiral When Threatened

A millipede's back is covered by hardened plates called tergites, but its underside is soft and vulnerable. Millipedes aren't fast, so they cannot outrun their predators. Instead, when a millipede feels it is in danger, it will coil its body into a tight spiral, protecting its belly.

Some Millipedes Practice "Chemical Warfare"

Millipedes are fairly docile critters. They don't bite. They can't sting. And they don't have pincers to fight back. But millipedes do carry secret chemical weapons. Some millipedes, for example, have stink glands (called ozopores) from which they emit a foul-smelling and awful tasting compound to repel predators. The chemicals produced by certain millipedes can burn or blister the skin if you handle them. Always wash your hands after holding a millipede, just to be safe.

Male Millipedes Court Females With Songs and Back Rubs

Unfortunately for the male, a female millipede will often take his attempts to mate with her as a threat. She'll curl up tightly, preventing him from delivering any sperm. The male millipede might walk on her back, convincing her to relax with the gentle massage provided by hundreds of his feet. In some species, the male can stridulate, producing a sound that calms his mate. Other male millipedes use sex pheromones to arouse a partner's interest in him.

Male Millipedes Have Special "Sex" Legs Called Gonopods

If a female is receptive to his advances, the male uses specially modified legs to transfer his spermatophore, or sperm packet, to her. She receives the sperm in her vulvae, just behind her second pair of legs. In most millipede species, the gonopods replace the legs on the 7th segment. You can usually tell if a millipede is male or female by examining this segment. A male will have short stumps in place of his legs, or no legs at all.

Millipedes Lay Their Eggs In Nests

Mother millipedes burrow into the soil and dig nests where they lay their eggs. In many cases, the mother millipede uses her own feces—her castings are just recycled plant matter after all—to construct a protective capsule for her offspring. In some instances, the millipede may push the soil with her hind end to mold the nest. She'll deposit 100 eggs or more (depending on her species) in the nest, and the hatchlings will emerge in roughly a month.

Millipedes Live Long Lives

Most arthropods have short life spans, but millipedes aren't your average arthropods. They're surprisingly long-lived. Millipedes follow the motto "slow and steady wins the race." They aren't flashy or fast, and they live rather boring lives as decomposers. Their passive defense strategy of camouflage serves them well, as they outlast many of their invertebrate cousins.

Millipedes Were the First Animals to Live on Land

Fossil evidence suggests that millipedes were the earliest animals to breathe air and make the move from water to land. Pneumodesmus newmani, a fossil found in siltstone in Scotland, dates back 428 million years, and is the oldest fossil specimen with spiracles for breathing air.

Sources

• NWF Field Guide to Insects and Spiders, Arthur V. Evans
• Fossil find oldest land animal. BBC News, January 25, 2004.
• Millipedes Made Easy, The Field Museum, Chicago, IL.
• Millipedes: Diplopoda, Earthlife Web, Gordon Ramel.