Harpaphe haydeniana is a millipede

Millipede

Millipedes are arthropods that have two pairs of legs per segment . Each segment that has two pairs of legs is a result of two single segments fused together as one...

 found in the moist forests along the Pacific coast

Pacific Ocean

The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

 of North America

North America

North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

, from California

California

California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

 to British Columbia

British Columbia

British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...

 and Alaska

Alaska

Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...

.

H. haydeniana reach a length of 4–5 cm (1.6–2 ) when mature

Sexual maturity

Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...

, and may live for 2–3 years. The body is black, 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

Arthropod leg

The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments are of Latin origin, and may be confused with terms for bones: coxa , trochanter , femur, tibia, tarsus, ischium, metatarsus, carpus, dactylus ,...

. The difference between males and females is due to one pair of legs on the seventh segment being modified in the male to form gonopods used for sperm

Sperm

The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...

 transfer.

H. haydeniana is an important part of the forest ecosystem

Ecosystem

An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....

, breaking down leaf litter, and freeing up its nutrients for other organisms. Immature millipedes feed on humus.

H. haydeniana has few predators, due to its aposematic coloration and its ability to secrete

Secretion

Secretion is the process of elaborating, releasing, and oozing chemicals, or a secreted chemical substance from a cell or gland. In contrast to excretion, the substance may have a certain function, rather than being a waste product...

 hydrogen cyanide when threatened. This behaviour gives rise to the common names "cyanide millipede" and "almond-scented millipede" (since cyanide

Cyanide

A cyanide is a chemical compound that contains the cyano group, -C≡N, which consists of a carbon atom triple-bonded to a nitrogen atom. Cyanides most commonly refer to salts of the anion CN−. Most cyanides are highly toxic....

 smells of almond

Almond

The almond , is a species of tree native to the Middle East and South Asia. Almond is also the name of the edible and widely cultivated seed of this tree...

s). Nonetheless, at least one species, the ground beetle

Ground beetle

Ground beetles are a large, cosmopolitan family of beetles, Carabidae, with more than 40,000 species worldwide, approximately 2,000 of which are found in North America and 2,700 in Europe.-Description and ecology:...

 Promecognathus laevissimus, is a specialised predator of H. haydeniana.