Yellow-spotted Millipede

The yellow-spotted millipede is a large, boldly patterned polydesmid millipede native to the humid forests of the Pacific coast of North America, from British Columbia to California. Its glossy black body and evenly spaced row of yellow to orange-yellow spots along each side make it one of the easiest millipedes to identify on sight.

As a detritivore, this species is a major contributor to leaf litter decomposition in the redwood and Douglas-fir forests it inhabits, and its conspicuous coloration is thought to serve as a warning signal to potential predators about its chemical defenses. It is frequently encountered crossing trails and forest floors, especially in the wetter months of the year.

• Glossy black or dark brown body with a single row of bright yellow-orange spots along each side
• Flattened, keeled body typical of the order Polydesmida, with about 20 segments
• Adults reach roughly 4-5 cm in length
• Short, clubbed antennae and no visible eyes
• Coils into a tight spiral when disturbed rather than rolling into a ball
• Distinguished from other Pacific Northwest millipedes by its high-contrast black-and-yellow pattern

Restricted largely to the Pacific coast of North America, from southern British Columbia through Washington, Oregon, and into northern California, favoring damp coniferous and mixed forests with abundant leaf litter, downed wood, and consistently high humidity. It is especially common in redwood and Douglas-fir forest floors and can be abundant after autumn and winter rains.

This millipede feeds on decomposing leaves, needles, and rotting wood, breaking down tough plant fibers and cycling nutrients back into forest soil. It is most active on the surface during cool, wet weather and retreats into deeper litter or soil during dry conditions. When threatened, it produces a defensive secretion from glands along its body, accompanied by a noticeable almond-like scent, and its bright coloring is believed to warn predators of this chemical defense. It moves slowly and relies almost entirely on these passive defenses rather than fleeing.

Eggs are laid in moist soil or leaf litter, and juveniles hatch with fewer segments and legs than adults, gaining both with each molt over a period of several years. Development to full maturity is slow compared to many insects, and individuals can live for several years, overwintering in sheltered litter or soil during colder months and becoming most visible during the wetter, cooler seasons.