A dark gray millipede crawling through a key ring placed in its path. American Giant Millipede. Narceus americanus.

Wild Facts About The American Giant Millipede

ByChristine Wild Animals

Modular Millipedes

  • The first and most obvious thing one will notice about an Giant American Millipede is its impressive size.
  • American Giant Millipedes are arthropods that can grow up to four inches (10 cm) long in total body length.
    • At first glance, they resemble worms, thanks to their long, flexible, cylindrical bodies.
      • In fact, one of their common names is “worm millipede”.
  • American Giant Millipede bodies consist of many, many connected segments, each of which is covered in tough, dorsal tergites.
    • American Giant Millipedes are dark gray, with thin, reddish stripes between their body segments and slightly pink legs.
      • They have one pair of thin, short antennae.
    • The underside of each segment is soft and flexible.
    • This segmented body structure gives the millipedes a lot of flexibility and a sinuous appearance.
  • This species adds additional body segments over time.
    • When they first hatch from eggs, American Giant Millipedes have only a few segments.
    • Periodically, they shed their tough, inflexible body coverings periodically (called “molting”) to allow their bodies to get bigger.
    • They add additional body segments with every molt until they reach full maturity.
Close-up of long, many-segmented gray and rust millipede covered in dewdrops. American Giant Millipede. Narceus americanus.
Close up of an American Giant Millipede Narceus americanus Photograph taken and design created by the author Copyright © 2025 Now I Wonder All rights reserved

How Many Legs Does One Millipede Need?

  • The second thing one might notice about an American Giant Millipede is that this wild animal—that looks much like a worm at first glance—has a truly tremendous number of legs.
  • American Giant Millipedes are diplopods, which means that almost every body segment bears two pairs of segmented legs.
    • In fact, the term “millipede” literally means “thousand feet”.
    • Although no millipede truly has a thousand feet, fully-grown Giant American Millipedes can have around 100 legs.
A long, dark, cylindrical millipede crawling next to a key for scale. American Giant Millipede. Narceus americanus.
American Giant Millipede Narceus americanus Photograph taken and design created by the author Copyright © 2025 Now I Wonder All rights reserved

Calm And Peaceful Little Detritivores

  • American Giant Millipedes are detritivores; they eat mostly decaying wood and leaf litter.
    • They live in forests and damp, humid environments throughout the eastern United States.
    • Mostly active at night, these millipedes can be spotted during the day, especially after heavy rains or during humid mornings.
  • Because they’re detritivores, these millipedes spend most of their time buried in leaf litter.
    • Their bodies are adapted to plowing head-first through leaf litter and soil.
      • The collum (the animal’s “head”) curves downward and is protected by a tough, abrasion-resistant covering impregnated with calcium salts.
      • Coordinated effort by their many, many legs push the millipedes through obstacles.
  • These wild animals help recycle nutrients into the soil, which then supports entire forest ecosystems.
A long, dark millipede crawling on pavement with the toe of a show for scale. American Giant Millipede. Narceus americanus.
American Giant Millipede Narceus americanus Photograph taken and design created by the author Copyright © 2025 Now I Wonder All rights reserved

Fortresses Filled With Cyanide

  • Because of their large size, American Giant Millipedes make tempting targets for many different predators.
  • But these invertebrates are far from defenseless.
  • American Giant Millipedes defend themselves against predators in two ways:
    • They curl up into defensive spirals (a behavior called “conglobation” and/or “volvation”) that protect their vulnerable undersides by exposing their tough, outer body covering.
    • They exude foul, caustic chemicals related to the poison cyanide through special body pores.
  • Each strategy may defend against different predators.
    • Smaller predators like spiders may be unable to penetrate the coiled millipedes’ tough exoskeletons and may eventually abandon their attacks in favor of easier prey.
    • Larger predators—who could simply crush or swallow curled millipedes whole—may avoid attacking or fully killing the millipedes in response to the millipedes’ caustic, foul-smelling defensive chemicals (Duchesne and Careau 2022, https://doi.org/10.1007/s00265-022-03217-2).

When Even Cyanide Isn’t Enough

  • Alas, no wild animal is ever entirely safe from being killed and eaten.
    • Despite their best efforts, American Giant Millipedes still get attacked and eaten by a number of predators.
  • Large vertebrate predators of American Giant Millipedes include:
  • Smaller invertebrate predators include:
    • Spiders
    • Glowworms (Phengodes plumosa)
    • Assassin bugs, especially Millipede Assassins (Hemiptera: Reduviidae: subfamily Ectrichodiinae)
Close-up of a long, gray and brown millipede coiled up on a tree trunk. American Giant Millipede. Narceus americanus.
American Giant Millipede Narceus americanus Photograph taken and design created by the author Copyright © 2025 Now I Wonder All rights reserved

Scientific Classification

Kingdom

Animalia (animals)

Phylum

Arthropoda (arthropods)

Class

Diplopoda (diplopods)

Order

Spirobolida (round-backed millipedes)

Family

Spirobolidae

Genus

Narceus

Species

N. americanus

Scientific Name

Narceus americanus

American Giant Millipede Photo Gallery

Browse All Animals

A – Z By Common Name A – Z By Scientific Name

Browse By Type Of Animal

Amphibians Birds Insects Mammals Other Animals Reptiles Spiders

Browse By Animal Group

Alligators Beetles Butterflies And Moths Caterpillars Dragonflies And Damselflies Frogs And Toads Grasshoppers And Related Insects Landbirds Lizards Mammals Other Animals Raptors And Owls Salamanders Snakes Songbirds Spiders True Bugs Turtles Wasps And Related Insects Water Birds

Browse By Color

Black Black And White Blue Brown Gray Green Orange Red White Yellow

More animals are added regularly, so please visit again!

author avatar
Christine
Christine is the creator and author of NowIWonder.com, a website dedicated to the animals and plants that share our world, and the science that helps us understand them. Inspired by lifelong exploration and learning, Christine loves to share her knowledge with others who want to connect with wild faces and wild spaces.
See Full Bio