The dark coloration with contrasting yellow-tipped keels warn of its ability to exude toxic hydrogen cyanide as a defense.

The cyanide secretions are not dangerous to humans, but can cause irritation and pain if it contacts sensitive areas such as the mouth, eyes, or nose.

[1] Despite the various common names given the species, the coloration pattern, cyanide defense, and associated almond scent occur in other flat-backed millipedes around the world.

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

[4] 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.