Harpaphe haydeniana      Family: Xystodesmidae

Common name: cyanide millipede; almond-scented millipede; yellow-spotted millipede

Food: leaf litter; conifer needles

 Adult size: 1.5 – 2 in (4-5 cm) long

Type: Beneficial

Life cycle: 
            Generations per year: 2 – 5
            Egg: > 3 weeks
            Instar: unknown
            Adult: 2 – 3 years


Description & Life Cycle: Adult cyanide millipedes are quite distinct with their black colouring and bright yellow patches along both sides. The body consists of about 20 segments with males having 30 pairs of legs and females having 31 pairs.

Millipedes are oviparous (egg-laying) and mating begins in spring. Cyanide millipede females will lay anywhere from 30 to 300 eggs in a season, typically underneath a rotten tree or log. The young hatch into an immobile dupoid in three weeks or more. The dupoid then molts into a pale-coloured instar stage. Each subsequent instar molt produces another segment which is slightly darker until it reaches maturity and is fully black with its yellow patches on the side. Adults live for 2 to 3 years.


Special Notes: Harpaphe haydeniana is native to the Pacific Northwest from southeast Alaska to California and west as far as the Sierra Nevada Mountains. The adult millipedes play an important part in maintaining the health of the forest ecosystem by breaking down the leaf litter and releasing nutrients for other organisms through their digestive system. The immature millipedes feed on humus.

This millipede has few predators due to its ability to exude hydrogen cyanide through its exoskeleton. This secretion is relatively harmless to humans, although it may cause some skin irritation so be forewarned. If possible, wash affected area immediately with soap and water. A more extreme reaction will occur if any secretion should get into the eyes. Seek medical aid if this occurs. Small-sized pets…cats and dogs…may exhibit stronger reactions to the hydrogen cyanide if it should get into their eyes. Rinse with water immediately, if possible, and seek veterinary aid.


Remedial Actions: This insect is highly beneficial to the health of the forest ecosystem so no remedial action is needed. In fact, they should be respected and left to do the work they are meant to do. Unfortunately, in just one week, we have seen two Harpaphe haydeniana which had been stepped on and killed in our local forest.


Posted on July 15, 2020