by Donna Hill B.Sc. B.Ed. 1997

This black-bodied creature is often mistaken for a caterpillar because of its yellow spots along the edge of its long body and its slow crawling movements. Look closely and you will see the many pairs of jointed legs that a caterpillar does not have.

Millipedes are Myriapods, which means they have a short head, long segmented body and many pairs of legs. They also belong to the class Diplopoda, which can be recognized by having two pairs of legs on each body segment. When they walk, their legs appear to do the wave (like at a football game) because each segment has two pairs of legs that are lifted at the same time. There are more than 7500 kinds of millipedes identified in the world.

Millipedes are very ancient creatures, among the first land animals back in the Carboniferous Period. There are fossils of a giant millipede called Arthropleura, which grew to 1 meter long! There is a good web site on fossil millipedes: Millipede info

The Yellow-spotted Millipede lives in moist forest floors along the Pacific Coast of North America from California to Alaska.

A millipede moves though the leafy layer holding its slightly curled antennae in front of it to feel and smell the way. Its many legs are needed step over and around the leafy particles and its body is flattened so it can fit into cracks and crevices on the forest floor. It is a decomposer, which means it chews up leaves and other dead plant material and recycles it into soil. They are usually found in small numbers under rotting leaves and sometimes can be seen migrating across the path on dark damp days and nights.

Mating occurs mostly in the spring and several hundred poppy-seed sized eggs are laid clustered loosely in soil or leaf litter. Young millipedes are small and white, with only a few legs. They eat humus (highly decomposed plant litter). They will need to molt 7 times to grow to adulthood. When it's time to molt, they build a hollow chamber from soil, crawl inside and seal it completely. They remain inside for several weeks, shedding the old exoskeleton and adding new segments and legs. When their new exoskeleton is hardened, they chew a hole in the chamber and emerge. It takes them about two years to mature. Adults are a beautiful shiny black with yellow or orange spots on each side of their back. They have 20 segments and 31 leg pairs. To tell males from females, look at the seventh segment. Females have two pair of legs on that segment, while males appear to have only a single pair. The leg pair is actually there, but is modified into a gonopod for sperm transfer. You'll need a magnifying glass to see it. Yellow-spotted millipedes live to about 2 to 3 years of age.

Mating occurs mostly in the spring and several hundred poppy-seed sized eggs are laid clustered loosely in soil or leaf litter. Young millipedes are paler in color than adults (light grey body with pale yellow spots) and have fewer body segments (and less legs). Each time they shed their skin, they add a segment and become a slightly darker shade of grey and have slightly brighter yellow spots. Once are they are about 4 to 5 cm long, 0.75 cm wide with their black and yellow colors, they are mature and are able to reproduce. At this point they have about 20 segments and females have 31 pairs of legs (14 double pairs and 3 single pairs) while males have only 30. The 8th pair of legs from the back on adult males appear to be missing. The leg pair is actually there, but modified into a gonopod for sperm transfer. You'll need magnification to see it. Yellow-spotted millipedes live to about 2 to 3 years of age.

They are not eaten by many creatures because they can protect themselves in two ways. The first is to curl its body into a tight ball, ressembling a snail with the hard exo-skeleton protecting its back. The other way is to release a smell from small pores in each segment which can kill or scare off other small creatures. To humans, this smell is pleasant and smells like almond extract. But to small creatures such as beetles and shrews, the smell contains the chemical cyanide, which is toxic to them in very small dosages.

Like most animals that bite, sting, taste bad or smell bad, yellow-spotted millipedes have a warning coloration. The bright yellow spots on a black background serve to warn potential predators that they can protect themselves, much like a yellow and black paper wasp warns that it can sting. If a small animal survives a meeting with this millipede, it will avoid it next time it meets one. Interestingly, all other millipedes (of the same species and different species) seem to be immune to this toxin.

Despite the cyanide, some beetles still manage to eat Harpaphe. How they protect themselves from the cyanide isn't known. They may hold their breath (close their spiracles) while killing the millipede, or they may have special enzymes to detoxify cyanide.

After a few minutes of handling, this millipede no longer shows fear and will not curl up or give off its almond smell. It is a friendly fellow to humans, and often we cannot feel its footfalls as it walks slowly across our hands. They make a great animal for classroom studies and have few special requirements when living in a forest floor terrarium for a short time.

Next time you are walking in the forest, take time to look for one of these fascinating many-legged creatures. Roll over a log (make sure to put it back) or dig through some leaves and pick up a millipede to look a little closer. Give it a smell. You'll be surprised at the pleasant odor!

For more information on the millipede, please contact Nancy Baumeister , a PhD candidate, who is studying these interesting invertebrates at Oregon State University.