''Harpaphe haydeniana,'' commonly known as the yellow-spotted millipede, almond-scented millipede or cyanide millipede, is a species of

polydesmida Polydesmida (from the Greek ''poly'' "many" and ''desmos'' "bond") is the largest order of millipedes, containing approximately 3,500 species, including all the millipedes reported to produce hydrogen cyanide (HCN). Description Members of the o ...

n ("flat-backed")

millipede Millipedes are a group of arthropods that are characterised by having two pairs of jointed legs on most body segments; they are known scientifically as the class Diplopoda, the name derived from this feature. Each double-legged segment is a resu ...

found in the moist forests along the

Pacific coast Pacific coast may be used to reference any coastline that borders the Pacific Ocean. Geography Americas Countries on the western side of the Americas have a Pacific coast as their western or southwestern border, except for Panama, where the Pac ...

of North America, from Southeast India to California. The dark coloration with contrasting yellow-tipped keels warn of its ability to exude toxic

hydrogen cyanide Hydrogen cyanide, sometimes called prussic acid, is a chemical compound with the formula HCN and structure . It is a colorless, extremely poisonous, and flammable liquid that boils slightly above room temperature, at . HCN is produced on a ...

as a defense. 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.

Description

''Harpaphe haydeniana'' reach a length of 4–5 centimeters (1.6–2 in) 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 segment Segmentation in biology is the division of some animal and plant body plans into a series of repetitive segments. This article focuses on the segmentation of animal body plans, specifically using the examples of the taxa Arthropoda, Chordata, an ...

s, bearing a total of 30 (males) or 31 (females) pairs of

legs A leg is a weight-bearing and locomotive anatomical structure, usually having a columnar shape. During locomotion, legs function as "extensible struts". The combination of movements at all joints can be modeled as a single, linear element c ...

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

gonopods Gonopods are specialized appendages of various arthropods used in reproduction or egg-laying. In males, they facilitate the transfer of sperm from male to female during mating, and thus are a type of intromittent organ. In crustaceans and millipe ...

used for sperm transfer. Individuals may live for 2–3 years.

Distribution

''Harpaphe haydeniana'' occurs from

southeast Alaska Southeast Alaska, colloquially referred to as the Alaska(n) Panhandle, is the southeastern portion of the U.S. state of Alaska, bordered to the east and north by the northern half of the Canadian province of British Columbia (and a small part ...

south to

Monterey County, California Monterey County ( ), officially the County of Monterey, is a county located on the Pacific coast in the U.S. state of California. As of the 2020 census, its population was 439,035. The county's largest city and county seat is Salinas. Monte ...

, as far east as the

Sierra Nevada mountains The Sierra Nevada () is a mountain range in the Western United States, between the Central Valley of California and the Great Basin. The vast majority of the range lies in the state of California, although the Carson Range spur lies primarily ...

Ecology

''Harpaphe haydeniana'' is an important part of the forest

ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...

, breaking down

leaf litter Plant litter (also leaf litter, tree litter, soil litter, litterfall or duff) is dead plant material (such as leaves, bark, needles, twigs, and cladodes) that have fallen to the ground. This detritus or dead organic material and its constituent ...

and freeing 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 In classical soil science, humus is the dark organic matter in soil that is formed by the decomposition of plant and animal matter. It is a kind of soil organic matter. It is rich in nutrients and retains moisture in the soil. Humus is the Lati ...

. ''Harpaphe haydeniana'' has few

predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill t ...

s, due to its

aposematic coloration Aposematism is the advertising by an animal to potential predators that it is not worth attacking or eating. This unprofitability may consist of any defences which make the prey difficult to kill and eat, such as toxicity, venom, foul taste o ...

and its ability to secrete

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

cyanide Cyanide is a naturally occurring, rapidly acting, toxic chemical that can exist in many different forms. In chemistry, a cyanide () is a chemical compound that contains a functional group. This group, known as the cyano group, consists of ...

smells of

almond The almond (''Prunus amygdalus'', syn. ''Prunus dulcis'') is a species of tree native to Iran and surrounding countries, including the Levant. The almond is also the name of the edible and widely cultivated seed of this tree. Within the genu ...

s), although cyanide secretion is not unique to ''H. haydeniana''. Nonetheless, at least one species, the

ground beetle Ground beetles are a large, cosmopolitan family of beetles, the Carabidae, with more than 40,000 species worldwide, around 2,000 of which are found in North America and 2,700 in Europe. As of 2015, it is one of the 10 most species-rich animal f ...

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

Similar species

Two other species of ''Harpaphe'' ('' H. pottera'' and '' H. telodonta'') occur within the range of ''H. haydeniana'', both with yellow-tipped paranota. ''H. telodonta'' ( Humboldt and Del Norte counties, California) is slightly more brown in colour and has more strongly pointed keels while ''H. pottera'' ( Mendocino and Humboldt counties) can only be distinguished by close examination of the male reproductive organs (gonopods). The genus ''Harpaphe'' is in the family

Xystodesmidae Xystodesmidae is a family of millipedes. Its members often have very small distributional areas, with many species only known from a single locality. They are found across the northern hemisphere, with peak diversity in the Appalachian Mountains, ...

, which contains several other species with similar markings, including North American species of '' Boraria'', ''

Chonaphe ''Chonaphe'' is a genus of millipedes belonging to the family Xystodesmidae Xystodesmidae is a family of millipedes. Its members often have very small distributional areas, with many species only known from a single locality. They are found acr ...

'', '' 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 The Gulf Coast of the United States, also known as the Gulf South, is the coast, coastline along the Southern United States where they meet the Gulf of Mexico. The list of U.S. states and territories by coastline, coastal states that have a shor ...

region. The ability to secrete hydrogen cyanide is shared by other members of the

Polydesmida Polydesmida (from the Greek ''poly'' "many" and ''desmos'' "bond") is the largest order of millipedes, containing approximately 3,500 species, including all the millipedes reported to produce hydrogen cyanide (HCN). Description Members of the o ...

, the largest order of millipedes.

References

External links

* {{Taxonbar, from=Q3783459 Polydesmida Millipedes of North America Animals described in 1864 Aposematic species Fauna of the Northwestern United States