Overview
The Yellow-spotted Millipede (Harpaphe haydeniana), also widely recognized as the cyanide millipede or almond-scented millipede, is a keystone macro-decomposer native to the temperate rainforests of the Pacific Northwest. Instantly recognizable by its glossy jet-black exoskeleton accentuated with vibrant lemon-yellow lateral spots, this gentle arthropod plays an indispensable role in nutrient cycling, processing tons of fallen conifer needle litter annually. When threatened, it defends itself with a potent chemical weapon: secreting lethal hydrogen cyanide.
Biology and Physical Characteristics
Harpaphe haydeniana typically reaches lengths of four to five centimeters. Its segmented body features twenty distinct body rings and approximately 30 to 31 pairs of legs. The dorsal plate of each segment (paranota) extends laterally into square flanges bearing vivid yellow or orange patches that serve as an unambiguous warning of toxicity (aposematism). Under ultraviolet illumination, its exoskeleton fluoresces with a luminous greenish glow. When handled or harassed, specialized ozopores along its flanks discharge benzaldehyde and liquid mandelonitrile, which breaks down into gaseous hydrogen cyanide emitting a strong almond aroma.
Behavior and Ecology
Operating as an obligate detritivore, the Yellow-spotted Millipede feeds primarily on dead and decaying conifer needles (such as Douglas fir, Western hemlock, and Sitka spruce), digesting lignin and cellulose with the aid of symbiotic gut microorganisms. Its digestive activities accelerate soil formation and mycorrhizal fungal development. Because hydrogen cyanide is lethal to most small vertebrates and insects, Harpaphe haydeniana experiences very low predation pressure, though specialized carabid beetles (such as Promecognathus laevissimus) have evolved immunity and prey upon it exclusively.
Conservation and Human Impact
Assessed as biologically secure and Least Concern throughout its extensive Pacific coastal range, Harpaphe haydeniana remains highly abundant in both old-growth and mature second-growth temperate rainforests. Intensive commercial clear-cutting that strips canopy shade and desiccates forest floor microclimates temporarily reduces localized densities. Nevertheless, its adaptability to mixed riparian corridors and protected reserves (such as Olympic National Park and Redwood National and State Parks) ensures robust, healthy wild populations.
Interesting Factoid
A single adult Yellow-spotted Millipede carries enough mandelonitrile in its glandular reservoirs to generate approximately 0.6 milligrams of pure hydrogen cyanide—sufficient to kill a small songbird or rodent that attempts to eat it.
Last updated: October 2026