Harpaphe haydeniana

Appearance

''H. haydeniana'' reach a length of 4–5 centimeters 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 or 31 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

Naming

Two other species of ''Harpahe'' occur within the range of ''H. haydeniana'', both with yellow-tipped paranota. ''H. telodonta'' is slightly more brown in colour and has more strongly pointed keels while ''H. pottera'' can only be distinguished by close examination of the male reproductive organs .

The genus ''Harpaphe'' is in the family Xystodesmidae, which contains several other species with similar markings, including North American species of ''Boraria'', ''Chonaphe'', ''Paimokia'', ''Hybaphe'' and ''Montaphe''. Exact species determination requires examination of the male gonopods, but the sharply pointed posterior corners of the paranota can help distinguish ''Harpaphe'' from ''Hybaphe'' and ''Chonaphe''.

Outside of North America, superficially similar species include ''Anoplodesmus saussurii'' which has been mistakenly called ''H. haydeniana'', and ''Asiomorpha coarctata'' , the latter species being native to Southeast Asia but widely introduced around the world, including the American Gulf Coast region. The ability to secrete hydrogen cyanide is shared by other members of the Polydesmida, the largest order of millipedes.

Distribution

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

Habitat

''H. haydeniana'' is an important part of the forest ecosystem, breaking down leaf litter, and freeing up 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.

''H. 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" , 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''.