''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, with more than 5,000 species, including all the millipedes reported to produce hydrogen cyanide (HCN). This order is also the most diverse of ...

n ("flat-backed")

millipede Millipedes (originating from the Latin , "thousand", and , "foot") 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 derive ...

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 North America Countries on the western side of North America have a Pacific coast as their western or south-western border. One of th ...

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

, from Southeast Alaska to

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

. The dark coloration with contrasting yellow-tipped keels warn of its ability to exude toxic

hydrogen cyanide Hydrogen cyanide (formerly known as prussic acid) is a chemical compound with the chemical formula, formula HCN and structural formula . It is a highly toxic and flammable liquid that boiling, boils slightly above room temperature, at . HCN is ...

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 nos

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 sexual maturity, 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 segments, bearing a total of 30 (males) or 31 (females) pairs of legs. The difference between males and females is due to one pair of legs on the seventh segment in males being modified to form gonopods used for sperm transfer. Individuals may live for 2–3 years.

Distribution

''Harpaphe haydeniana'' occurs from southeast Alaska south to

Monterey County, California Monterey County ( ), officially the County of Monterey, is a county (United States), county located on the Pacific Ocean, Pacific coast in the U.S. state of California. As of the 2020 United States census, its population was 439,035. The count ...

, as far east as the Sierra Nevada mountains.

Ecology

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

ecosystem An ecosystem (or ecological system) is a system formed by Organism, organisms in interaction with their Biophysical environment, environment. The Biotic material, biotic and abiotic components are linked together through nutrient cycles and en ...

, 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 has fallen to the ground. This detritus or dead organic material and its constituen ...

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 in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation ...

s, due to its aposematic coloration and its ability to secrete

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

cyanide In chemistry, cyanide () is an inorganic chemical compound that contains a functional group. This group, known as the cyano group, consists of a carbon atom triple-bonded to a nitrogen atom. Ionic cyanides contain the cyanide anion . This a ...

smells of

almond The almond (''Prunus amygdalus'', Synonym (taxonomy)#Botany, syn. ''Prunus dulcis'') is a species of tree from the genus ''Prunus''. Along with the peach, it is classified in the subgenus ''Amygdalus'', distinguished from the other subgenera ...

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

ground beetle Ground beetles are a large, cosmopolitan distribution, cosmopolitan family (biology), 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 ...

'' Promecognathus laevissimus'', is a specialised predator of ''H. haydeniana''. Good for soil aeration. Non aggressive.

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, which contains several other species with similar markings, including North American species of '' Boraria'', '' Chonaphe'', '' 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 or the South Coast, is the coastline along the Southern United States where they meet the Gulf of Mexico. The coastal states that have a shoreline on the Gulf of Mexico are Tex ...

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, with more than 5,000 species, including all the millipedes reported to produce hydrogen cyanide (HCN). This order is also the most diverse of ...

, 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 Taxa named by Horatio Curtis Wood