Yellow-spotted Millipede

Harpaphe haydeniana reach a length of 4–5 centimeters (1.6–2 in) when mature. The upper surface of the body is black to olive green, and is distinctively marked along the sides with patches of a yellowish colour. H. haydeniana has approximately twenty body segments, bearing a total of 30 (males) or 31 (females) pairs of legs. The difference between males and females is due to one pair of legs on the seventh segment in males being modified to form gonopods used for sperm transfer. Individuals may live for 2–3 years.

Harpaphe haydeniana occurs from southeast Alaska south to Monterey County, California, as far east as the Sierra Nevada mountains.

Harpaphe haydeniana is an important part of the forest ecosystem, breaking down leaf litter and freeing its nutrients for other organisms. It is commonly associated with redwood forests where many individuals may be found within a small area. Immature millipedes feed on humus. Harpaphe haydeniana has few predators, due to its aposematic coloration and its ability to secrete hydrogen cyanide when threatened. This behaviour gives rise to the common names "cyanide millipede" and "almond-scented millipede" (since cyanide smells of almonds), although cyanide secretion is not unique to H. haydeniana. Nonetheless, at least one species, the ground beetle Promecognathus laevissimus, is a specialised predator of H. haydeniana.