Millipedes are a group of

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...

s 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 result of two single segments fused together. Most millipedes have very elongated cylindrical or flattened bodies with more than 20 segments, while

pill millipede Pill millipedes are any members of two living (and one extinct) orders of millipedes, often grouped together into a single superorder, Oniscomorpha. The name Oniscomorpha refers to the millipedes' resemblance to certain woodlice (Oniscidea), also ...

s are shorter and can roll into a tight ball. Although the name "millipede" derives from the

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

for "thousand feet", no species was known to have 1,000 or more until the discovery of ''

Eumillipes persephone ''Eumillipes'' is a genus of millipede in the family Siphonotidae. It contains a single species, ''E. persephone'', known from the Eastern Goldfields of Western Australia. The species was first collected in 2020, discovered in three drill holes, ...

'', which can have over 1,300 legs. There are approximately 12,000 named

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

classified into 16 orders and around 140

families Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Ideal ...

, making Diplopoda the largest class of

myriapod Myriapods () are the members of subphylum Myriapoda, containing arthropods such as millipedes and centipedes. The group contains about 13,000 species, all of them terrestrial. The fossil record of myriapods reaches back into the late Silurian, ...

s, an arthropod group which also includes centipedes and other multi-legged creatures. Most millipedes are slow-moving detritivores, eating decaying leaves and other dead plant matter. Some eat

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...

or drink plant fluids, and a small number are

predatory 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 th ...

. Millipedes are generally harmless to humans, although some can become household or garden pests. Millipedes can be an unwanted nuisance particularly in greenhouses where they can potentially cause severe damage to emergent seedlings. Most millipedes defend themselves with a variety of chemicals secreted from pores along the body, although the tiny

bristle millipede Polyxenida is an order of millipedes readily distinguished by a unique body plan consisting of a soft, non-calcified body ornamented with tufts of bristles – traits that have inspired the common names "bristly millipedes" or "pincushion millipe ...

s are covered with tufts of detachable bristles. Its primary defence mechanism is to curl into a tight coil, thereby protecting its legs and other vital delicate areas on the body behind a hard exoskeleton. Reproduction in most species is carried out by modified male legs called

gonopod 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 ...

s, which transfer packets of sperm to females. First appearing in the Silurian period, millipedes are some of the oldest known land animals. Some members of prehistoric groups, such as ''

Arthropleura ''Arthropleura'' () is a genus of extinct millipede arthropods that lived in what is now North America and Europe around 345 to 290 million years ago, from the Viséan stage of the lower Carboniferous Period to the Sakmarian stage of the lower ...

'', grew to over ; the largest modern species reach maximum lengths of . The longest extant species is the giant African millipede (''

Archispirostreptus gigas ''Archispirostreptus gigas'', known as the giant African millipede or shongololo, is the largest extant species of millipede, growing up to in length, in circumference. It has approximately 256 legs, although the number of legs changes with eac ...

''). Among myriapods, millipedes have traditionally been considered most closely related to the tiny

pauropod Pauropods are small, pale, millipede-like arthropods. Around 830 species in twelve families are found worldwide, living in soil and leaf mold. They look rather like centipedes, or millipedes, and may be a sister group of the latter. However, this ...

s, although some molecular studies challenge this relationship. Millipedes can be distinguished from the somewhat similar but only distantly related centipedes (class Chilopoda), which move rapidly, are

venom Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved ''venom apparatus'', such as fangs or a st ...

ous, carnivorous, and have only a single pair of legs on each body segment. The scientific study of millipedes is known as diplopodology, and a scientist who studies them is called a diplopodologist.

Etymology and names

The term "millipede" is widespread in popular and scientific literature, but among North American scientists, the term "milliped" (without the terminal e) is also used.
Other vernacular names include "thousand-legger" or simply "diplopod". The science of millipede biology and taxonomy is called diplopodology: the study of diplopods.

Classification

Approximately 12,000 millipede

have been described. Estimates of the true number of species on earth range from 15,000 to as high as 80,000. Few species of millipede are at all widespread; they have very poor dispersal abilities, depending as they do on terrestrial locomotion and humid habitats. These factors have favoured genetic isolation and rapid speciation, producing many lineages with restricted ranges. The living members of the Diplopoda are divided into sixteen orders in two subclasses. The basal subclass Penicillata contains a single order, Polyxenida (bristle millipedes). All other millipedes belong to the subclass Chilognatha consisting of two infraclasses: Pentazonia, containing the short-bodied pill millipedes, and Helminthomorpha (worm-like millipedes), containing the great majority of the species.

Outline of classification

The higher-level classification of millipedes is presented below, based on Shear, 2011, and Shear & Edgecombe, 2010 (extinct groups). Recent cladistic and molecular studies have challenged the traditional classification schemes above, and in particular the position of the orders Siphoniulida and Polyzoniida is not yet well established. The placement and positions of extinct groups (†) known only from fossils is tentative and not fully resolved. After each name is listed the author citation: the name of the person who coined the name or defined the group, even if not at the current rank. Class Diplopoda de Blainville in Gervais, 1844 * Subclass Penicillata Latreille, 1831 ** Order

Polyxenida Polyxenida is an order of millipedes readily distinguished by a unique body plan consisting of a soft, non-calcified body ornamented with tufts of bristles – traits that have inspired the common names "bristly millipedes" or "pincushion millipe ...

Verhoeff, 1934 * Subclass †

Arthropleuridea Arthropleuridea is an extinct subclass of myriapod arthropods that flourished during the Carboniferous period, having first arose during the Silurian, and perishing in the Early Permian. Members are characterized by possessing diplosegement (fuse ...

(placed in Penicillata by some authors) **Order † Arthropleurida Waterlot, 1934 ** Order † Eoarthropleurida Shear & Selden, 1995 ** Order † Microdecemplicida Wilson & Shear, 2000 * Subclass Chilognatha Latreille, 1802 ** Order † Zosterogrammida Wilson, 2005 (Chilognatha ''

incertae sedis ' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertain ...

'') ** Infraclass Pentazonia Brandt, 1833 *** Order † Amynilyspedida Hoffman, 1969 *** Superorder Limacomorpha Pocock, 1894 **** Order

Glomeridesmida Glomeridesmida is an order of millipedes in the infraclass Pentazonia containing 2 families and at least 31 species. Glomeridesmida is the only living order of the superorder Limacomorpha. Glomeridesmidans are small (less than ) and somewhat fl ...

Cook, 1895 *** Superorder Oniscomorpha Pocock, 1887 **** Order Glomerida Brandt, 1833 **** Order Sphaerotheriida Brandt, 1833 ** Infraclass Helminthomorpha Pocock, 1887 *** Superorder † Archipolypoda Scudder, 1882 **** Order † Archidesmida Wilson & Anderson 2004 **** Order † Cowiedesmida Wilson & Anderson 2004 **** Order † Euphoberiida Hoffman, 1969 **** Order † Palaeosomatida Hannibal & Krzeminski, 2005 *** Order † Pleurojulida Schneider & Werneburg, 1998 (possibly sister to Colobognatha) *** Subterclass Colobognatha Brandt, 1834 **** Order Platydesmida Cook, 1895 **** Order Polyzoniida Cook, 1895 **** Order Siphonocryptida Cook, 1895 **** Order Siphonophorida Newport, 1844 *** Subterclass Eugnatha Attems, 1898 **** Superorder Juliformia Attems, 1926 ***** Order

Julida Julida is an order (biology), order of millipedes. Members are mostly small and cylindrical, typically ranging from in length. Eyes may be present or absent, and in mature males of many species, the first pair of legs is modified into hook-like ...

Brandt, 1833 ***** Order Spirobolida Cook, 1895 ***** Order Spirostreptida Brandt, 1833 *****Superfamily † Xyloiuloidea Cook, 1895 (Sometimes aligned with Spirobolida) **** Superorder Nematophora Verhoeff, 1913 ***** Order

Callipodida Callipodida is an order of millipedes containing around 130 species, many characterized by crests or ridges. Description Callipodida are long and narrow millipedes, up to in length with 40-60 body segments. A dorsal groove is present running ...

Pocock, 1894 ***** Order

Chordeumatida Chordeumatida (from the Greek word for "sausage") is a large order of millipedes containing some 1200 species with a nearly worldwide distribution. Also known as "sausage millipedes," they possess around 30 body segments behind the head (includi ...

Pocock 1894 ***** Order Stemmiulida Cook, 1895 ***** Order Siphoniulida Cook, 1895 **** Superorder Merocheta Cook, 1895 ***** Order

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 ...

Pocock, 1887

Evolution

Millipedes are among the first animals to have colonised land during the

Silurian period The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozo ...

. Early forms probably ate mosses and primitive

vascular plant Vascular plants (), also called tracheophytes () or collectively Tracheophyta (), form a large group of land plants ( accepted known species) that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They ...

s. There are two major groups of millipedes whose members are all extinct: the Archipolypoda ("ancient, many-legged ones") which contain the oldest known terrestrial animals, and

, which contain the largest known land invertebrates. The earliest known land creature, ''

Pneumodesmus newmani ''Pneumodesmus newmani'' is a species of myriapod that lived in the Paleozoic. Its exact age is uncertain; it was originally interpreted as living , in the Late Silurian; however, subsequent research dates it to around 414 million years old, i ...

'', was an archipolypodan known from long fragment that lived 414 million years ago in the early Devonian, and has clear evidence of spiracles (breathing holes) attesting to its air-breathing habits. During the Upper Carboniferous (), ''

'' became the largest known land-dwelling invertebrate on record, reaching lengths of at least . Millipedes also exhibit the earliest evidence of chemical defence, as some Devonian fossils have defensive gland openings called

ozopore An ozopore is the opening of a defensive gland present in some arthropods, notably in millipedes of the order Polydesmida Anadenobolus monilicornis 03

The history of scientific millipede classification began with

Carl Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his Nobility#Ennoblement, ennoblement in 1761 as Carl von Linné#Blunt, Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalise ...

, who in his 10th edition of ''Systema Naturae'', 1758, named seven species of '' Julus'' as "Insecta Aptera" (wingless insects). In 1802, the French zoologist

Pierre André Latreille Pierre André Latreille (; 29 November 1762 – 6 February 1833) was a French zoologist, specialising in arthropods. Having trained as a Roman Catholic priest before the French Revolution, Latreille was imprisoned, and only regained his freedom ...

proposed the name Chilognatha as the first group of what are now the Diplopoda, and in 1840 the German naturalist Johann Friedrich von Brandt produced the first detailed classification. The name Diplopoda itself was coined in 1844 by the French zoologist

Henri Marie Ducrotay de Blainville Henri Marie Ducrotay de Blainville (; 12 September 1777 – 1 May 1850) was a French zoologist and anatomist. Life Blainville was born at Arques, near Dieppe. As a young man he went to Paris to study art, but ultimately devoted himself to natur ...

. From 1890 to 1940, millipede taxonomy was driven by relatively few researchers at any given time, with major contributions by Carl Attems, Karl Wilhelm Verhoeff and

Ralph Vary Chamberlin Ralph Vary Chamberlin (January 3, 1879October 31, 1967) was an American biologist, ethnographer, and historian from Salt Lake City, Utah. He was a faculty member of the University of Utah for over 25 years, where he helped establish the School ...

, who each described over 1,000 species, as well as Orator F. Cook, Filippo Silvestri, R. I. Pocock, and Henry W. Brölemann. This was a period when the science of diplopodology flourished: rates of species descriptions were on average the highest in history, sometimes exceeding 300 per year. In 1971, the Dutch biologist C. A. W. Jeekel published a comprehensive listing of all known millipede genera and families described between 1758 and 1957 in his ''Nomenclator Generum et Familiarum Diplopodorum'', a work credited as launching the "modern era" of millipede taxonomy. In 1980, the American biologist

Richard L. Hoffman Richard Lawrence Hoffman (September 25, 1927 – June 10, 2012) was an American zoologist known as an international expert on millipedes, and a leading authority on the natural history of Virginia and the Appalachian Mountains. He was a biology ...

published a classification of millipedes which recognized the Penicillata, Pentazonia, and Helminthomorpha, and the first phylogenetic analysis of millipede orders using modern cladistic methods was published in 1984 by Henrik Enghoff of Denmark. A 2003 classification by the American myriapodologist Rowland Shelley is similar to the one originally proposed by Verhoeff, and remains the currently accepted classification scheme (shown below), despite more recent molecular studies proposing conflicting relationships. A 2011 summary of millipede family diversity by William A. Shear placed the order Siphoniulida within the larger group Nematophora.

Fossil record

In addition to the 16 living orders, there are 9 extinct orders and one superfamily known only from fossils. The relationship of these to living groups and to each other is controversial. The extinct Arthropleuridea was long considered a distinct myriapod class, although work in the early 21st century established the group as a subclass of millipedes. Several living orders also appear in the fossil record. Below are two proposed arrangements of fossil millipede groups. Extinct groups are indicated with a

dagger A dagger is a fighting knife with a very sharp point and usually two sharp edges, typically designed or capable of being used as a thrusting or stabbing weapon.State v. Martin, 633 S.W.2d 80 (Mo. 1982): This is the dictionary or popular-use de ...

(†). The extinct order Zosterogrammida, a chilognath of uncertain position, is not shown.

Relation to other myriapods

Although the relationships of millipede orders are still the subject of debate, the class Diplopoda as a whole is considered a

monophyletic group A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

of arthropods: all millipedes are more closely related to each other than to any other arthropods. Diplopoda is a class within the arthropod subphylum

Myriapoda Myriapods () are the members of subphylum Myriapoda, containing arthropods such as millipedes and centipedes. The group contains about 13,000 species, all of them terrestrial. The fossil record of myriapods reaches back into the late Silurian ...

, the myriapods, which includes centipedes (class Chilopoda) as well as the lesser-known pauropods (class Pauropoda) and

symphyla Symphylans, also known as garden centipedes or pseudocentipedes, are soil-dwelling arthropods of the class Symphyla in the subphylum Myriapoda. Symphylans resemble centipedes, but are very small, non-venomous, and only distantly related to both ...

ns (class Symphyla). Within myriapods, the closest relatives or sister group of millipedes has long been considered the pauropods, which also have a collum and diplosegments.

Distinction from centipedes

The differences between millipedes and centipedes are a common question from the general public. Both groups of myriapods share similarities, such as long, multi-segmented bodies, many legs, a single pair of antennae, and the presence of postantennal organs, but have many differences and distinct evolutionary histories, as the

most recent common ancestor In biology and genetic genealogy, the most recent common ancestor (MRCA), also known as the last common ancestor (LCA) or concestor, of a set of organisms is the most recent individual from which all the organisms of the set are descended. The ...

of centipedes and millipedes lived around 450 to 475 million years ago in the Silurian. The head alone exemplifies the differences; millipedes have short, geniculate (elbowed) antennae for probing the substrate, a pair of robust mandibles and a single pair of maxillae fused into a lip; centipedes have long, threadlike antennae, a pair of small mandibles, two pairs of maxillae and a pair of large poison claws. Millipede centipede side-by-side

Characteristics

Millipedes come in a variety of body shapes and sizes, ranging from to around in length, and can have as few as eleven to over three hundred segments. They are generally black or brown in colour, although there are a few brightly coloured species, and some have

aposematic 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 ...

colouring to warn that they are toxic. Species of '' Motyxia'' produce

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 ...

as a chemical defence and are bioluminescent. Body styles vary greatly between major millipede groups. In the basal subclass Penicillata, consisting of the tiny

s, the exoskeleton is soft and uncalcified, and is covered in prominent

seta In biology, setae (singular seta ; from the Latin word for " bristle") are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Annelid setae are stiff bristles present on the body. ...

e or bristles. All other millipedes, belonging to the subclass Chilognatha, have a hardened exoskeleton. The chilognaths are in turn divided into two infraclasses: the Pentazonia, containing relatively short-bodied groups such as

s, and the Helminthomorpha ("worm-like" millipedes), which contains the vast majority of species, with long, many-segmented bodies. They have also lost the gene that codes for the JHAMTl enzyme, which is responsible for catalysing the last step of the production of a juvenile hormone that regulates the development and reproduction in other arthropods like crustaceans, centipedes and insects.

Head

The head of a millipede is typically rounded above and flattened below and bears a pair of large

mandibles In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

in front of a plate-like structure called a gnathochilarium ("jaw lip"). The head contains a single pair of antennae with seven or eight segments and a group of sensory cones at the tip. Many orders also possess a pair of sensory organs known as the Tömösváry organs, shaped as small oval rings posterior and lateral to the base of the antennae. Their function is unknown, but they also occur in some centipedes, and are possibly used to measure humidity or light levels in the surrounding environment. Millipede eyes consist of several simple flat-lensed

ocelli A simple eye (sometimes called a pigment pit) refers to a form of eye or an optical arrangement composed of a single lens and without an elaborate retina such as occurs in most vertebrates. In this sense "simple eye" is distinct from a multi-l ...

arranged in a group or patch on each side of the head. These patches are also called ocular fields or ocellaria. Many species of millipedes, including the entire orders

, Siphoniulida,

, Siphonophorida and Platydesmida, and cave-dwelling millipedes such as '' Causeyella'' and '' Trichopetalum'', had ancestors that could see but have subsequently lost their eyes and are blind.

Body

Millipede bodies may be flattened or cylindrical, and are composed of numerous metameric segments, each with an

exoskeleton An exoskeleton (from Greek ''éxō'' "outer" and ''skeletós'' "skeleton") is an external skeleton that supports and protects an animal's body, in contrast to an internal skeleton (endoskeleton) in for example, a human. In usage, some of the ...

consisting of four chitinous plates: a single plate above (the

tergite A ''tergum'' (Latin for "the back"; plural ''terga'', associated adjective tergal) is the dorsal ('upper') portion of an arthropod segment other than the head. The anterior edge is called the 'base' and posterior edge is called the 'apex' or 'mar ...

), one at each side (

pleurite A sclerite (Greek , ', meaning " hard") is a hardened body part. In various branches of biology the term is applied to various structures, but not as a rule to vertebrate anatomical features such as bones and teeth. Instead it refers most commonly ...

s), and a plate on the underside ( sternite) where the legs attach. In many millipedes, such as Merocheta and Juliformia, these plates are fused to varying degrees, sometimes forming a single cylindrical ring. The plates are typically hard, impregnated with calcium salts. Because they can't close their permanently open spiracles and most species lack a waxy cuticle, millipedes are susceptible to water loss and with a few exceptions must spend most of their time in moist or humid environments. The first segment behind the head is legless and known as a collum (from the Latin for neck or collar). The second, third, and fourth body segments bear a single pair of legs each and are known as "haplosegments" (the three haplosegments are sometimes referred to as a "

thorax The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the cre ...

"). The remaining segments, from the fifth to the posterior, are properly known as diplosegments or double segments, formed by the fusion of two embryonic segments. Each diplosegment bears two pairs of legs, rather than just one as in centipedes. In some millipedes, the last few segments may be legless. The terms "segment" or "body ring" are often used interchangeably to refer to both haplo- and diplosegments. The final segment is known as the

telson The telson () is the posterior-most division of the body of an arthropod. Depending on the definition, the telson is either considered to be the final segment of the arthropod body, or an additional division that is not a true segment on accou ...

and consists of a legless preanal ring, a pair of anal valves (closeable plates around the anus), and a small scale below the anus. Millipedes in several orders have keel-like extensions of the body-wall known as paranota, which can vary widely in shape, size, and texture; modifications include lobes, papillae, ridges, crests, spines and notches. Paranota may allow millipedes to wedge more securely into crevices, protect the legs, or make the millipede more difficult for predators to swallow. The legs are composed of seven segments, and attach on the underside of the body. The legs of an individual are generally rather similar to each other, although often longer in males than females, and males of some species may have a reduced or enlarged first pair of legs. The most conspicuous leg modifications are involved in reproduction, discussed below. Despite the common name, no millipede was known to have 1,000 legs until 2021: common species have between 34 and 400 legs, and the record is held by ''

'', with individuals possessing up to 1,306 legs – more than any other creature on Earth.

Internal organs

Millipedes breathe through two pairs of spiracles located ventrally on each segment near the base of the legs. Each opens into an internal pouch, and connects to a system of tracheae. The heart runs the entire length of the body, with an

aorta The aorta ( ) is the main and largest artery in the human body, originating from the left ventricle of the heart and extending down to the abdomen, where it splits into two smaller arteries (the common iliac arteries). The aorta distributes o ...

stretching into the head. The excretory organs are two pairs of

malpighian tubule The Malpighian tubule system is a type of excretory and osmoregulatory system found in some insects, myriapods, arachnids and tardigrades. The system consists of branching tubules extending from the alimentary canal that absorbs solutes, water, ...

s, located near the mid-part of the gut. The digestive tract is a simple tube with two pairs of

salivary gland The salivary glands in mammals are exocrine glands that produce saliva through a system of ducts. Humans have three paired major salivary glands ( parotid, submandibular, and sublingual), as well as hundreds of minor salivary glands. Salivary ...

s to help digest the food.

Reproduction and growth

Millipedes show a diversity of mating styles and structures. In the basal order

(bristle millipedes), mating is indirect: males deposit

spermatophore A spermatophore or sperm ampulla is a capsule or mass containing spermatozoa created by males of various animal species, especially salamanders and arthropods, and transferred in entirety to the female's ovipore during reproduction. Spermatophores ...

s onto webs they secrete with special glands, and the spermatophores are subsequently picked up by females. In all other millipede groups, males possess one or two pairs of modified legs called

s which are used to transfer sperm to the female during copulation. The location of the gonopods differs between groups: in males of the Pentazonia they are located at the rear of the body and known as telopods and may also function in grasping females, while in the Helminthomorpha – the vast majority of species – they are located on the seventh body segment. A few species are

parthenogenetic Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction in which growth and developmen ...

, having few, if any, males. Gonopods occur in a diversity of shapes and sizes, and in the range from closely resembling walking legs to complex structures quite unlike legs at all. In some groups, the gonopods are kept retracted within the body; in others they project forward parallel to the body. Gonopod morphology is the predominant means of determining species among millipedes: the structures may differ greatly between closely related species but very little within a species. The gonopods develop gradually from walking legs through successive moults until reproductive maturity. Anamorphic development in Nemasoma

The genital openings (

gonopore A gonopore, sometimes called a gonadopore, is a genital pore in many invertebrates. Hexapods, including insects have a single common gonopore, except mayflies, which have a pair of gonopores. More specifically, in the unmodified female it is t ...

s) of both sexes are located on the underside of the third body segment (near the second pair of legs) and may be accompanied in the male by one or two penes which deposit the sperm packets onto the gonopods. In the female, the genital pores open into paired small sacs called

cyphopod Cyphopods, also known as vulvae, are paired sacs in female millipedes that located on the underside of the third body segment that store sperm and connect to the oviduct The oviduct in mammals, is the passageway from an ovary. In human females th ...

s or vulvae, which are covered by small hood-like lids, and are used to store the sperm after copulation. The cyphopod morphology can also be used to identify species. Millipede sperm lack flagella, a unique trait among myriapods. In all except the bristle millipedes, copulation occurs with the two individuals facing one another. Copulation may be preceded by male behaviours such as tapping with antennae, running along the back of the female, offering edible glandular secretions, or in the case of some pill-millipedes,

stridulation Stridulation is the act of producing sound by rubbing together certain body parts. This behavior is mostly associated with insects, but other animals are known to do this as well, such as a number of species of fish, snakes and spiders. The mech ...

or "chirping". During copulation in most millipedes, the male positions his seventh segment in front of the female's third segment, and may insert his gonopods to extrude the vulvae before bending his body to deposit sperm onto his gonopods and reinserting the "charged" gonopods into the female. Females lay from ten to three hundred eggs at a time, depending on species, fertilising them with the stored sperm as they do so. Many species deposit the eggs on moist soil or organic detritus, but some construct nests lined with dried

faeces Feces ( or faeces), known colloquially and in slang as poo and poop, are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the large intestine. Feces contain a relati ...

, and may protect the eggs within silk cocoons. In most species, the female abandons the eggs after they are laid, but some species in the orders Platydesmida and Stemmiulida provide

parental care Parental care is a behavioural and evolutionary strategy adopted by some animals, involving a parental investment being made to the evolutionary fitness of offspring. Patterns of parental care are widespread and highly diverse across the animal ki ...

for eggs and young. The young hatch after a few weeks, and typically have only three pairs of legs, followed by up to four legless segments. As they grow, they continually

moult In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is the manner in which an animal routinely casts off a part of its body (often, but not always, an outer ...

, adding further segments and legs as they do so. Some species moult within specially prepared chambers of soil or silk, and may also shelter in these during wet weather, and most species eat the discarded exoskeleton after moulting. The adult stage, when individuals become reproductively mature, is generally reached in the final moult stage, which varies between species and orders, although some species continue to moult after adulthood. Furthermore, some species alternate between reproductive and non-reproductive stages after maturity, a phenomenon known as periodomorphosis, in which the reproductive structures regress during non-reproductive stages. Millipedes may live from one to ten years, depending on species.

Ecology

Habitat and distribution

Millipedes occur on all continents except Antarctica, and occupy almost all terrestrial habitats, ranging as far north as the Arctic Circle in Iceland, Norway, and Central Russia, and as far south as

Santa Cruz Province, Argentina Santa Cruz Province ( es, Provincia de Santa Cruz, , 'Holy Cross') is a province of Argentina, located in the southern part of the country, in Patagonia. It borders Chubut Province to the north, and Chile to the west and south, with an Atlantic c ...

. Typically forest floor dwellers, they live in leaf litter, dead wood, or soil, with a preference for humid conditions. In temperate zones, millipedes are most abundant in moist deciduous forests, and may reach densities of over 1,000 individuals per square metre. Other habitats include coniferous forests, caves, and alpine ecosystems. Deserticolous millipedes, species evolved to live in the desert, like Orthoporus ornatus, may show adaptations like a waxy epicuticle and the ability of water uptake from unsaturated air. Some species can survive freshwater floods and live submerged underwater for up to 11 months. A few species occur near the seashore and can survive in somewhat salty conditions.

Burrowing

The diplosegments of millipedes have evolved in conjunction with their burrowing habits, and nearly all millipedes adopt a mainly subterranean lifestyle. They use three main methods of burrowing; bulldozing, wedging and boring. Members of the orders

, Spirobolida and Spirostreptida, lower their heads and barge their way into the substrate, the collum leading the way. Flat-backed millipedes in the order

tend to insert their front end, like a wedge, into a horizontal crevice, and then widen the crack by pushing upwards with their legs, the paranota in this instance constituting the main lifting surface. Boring is used by members of the order Polyzoniida. These have smaller segments at the front and increasingly large ones further back; they propel themselves forward into a crack with their legs, the wedge-shaped body widening the gap as they go. Some millipedes have adopted an above-ground lifestyle and lost the burrowing habit. This may be because they are too small to have enough leverage to burrow, or because they are too large to make the effort worthwhile, or in some cases because they move relatively fast (for a millipede) and are active predators.

Diet

Most millipedes are detritivores and feed on decomposing vegetation, feces, or organic matter mixed with soil. They often play important roles in the breakdown and

decomposition Decomposition or rot is the process by which dead organic substances are broken down into simpler organic or inorganic matter such as carbon dioxide, water, simple sugars and mineral salts. The process is a part of the nutrient cycle and is e ...

plant 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 constitue ...

: estimates of consumption rates for individual species range from 1 to 11 percent of all leaf litter, depending on species and region, and collectively millipedes may consume nearly all the leaf litter in a region. The leaf litter is fragmented in the millipede gut and excreted as pellets of leaf fragments, algae, fungi, and bacteria, which facilitates decomposition by the microorganisms. Where

earthworm An earthworm is a terrestrial invertebrate that belongs to the phylum Annelida. They exhibit a tube-within-a-tube body plan; they are externally segmented with corresponding internal segmentation; and they usually have setae on all segments. T ...

populations are low in tropical forests, millipedes play an important role in facilitating microbial decomposition of the leaf litter. Some millipedes are herbivorous, feeding on living plants, and some species can become serious pests of crops. Millipedes in the order

graze algae from bark, and Platydesmida feed on fungi. A few species are

omnivorous An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nut ...

or in

and

occasionally carnivorous, feeding on insects, centipedes, earthworms, or

snails A snail is, in loose terms, a shelled gastropod. The name is most often applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class Gastro ...

. Some species have piercing mouth parts that allow them to suck up plant juices.

Predators and parasites

Millipedes are preyed on by a wide range of animals, including various reptiles, amphibians,

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...

s, mammals, and

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three ...

s. Mammalian predators such as

coati Coatis, also known as coatimundis (), are members of the family Procyonidae in the genera ''Nasua'' and ''Nasuella''. They are diurnal mammals native to South America, Central America, Mexico, and the southwestern United States. The name ...

s and meerkats roll captured millipedes on the ground to deplete and rub off their defensive secretions before consuming their prey, and certain poison dart frogs are believed to incorporate the toxic compounds of millipedes into their own defences. Several invertebrates have specialised behaviours or structures to feed on millipedes, including larval glowworm beetles, ''

Probolomyrmex ''Probolomyrmex'' is a genus of ants in the subfamily Proceratiinae. The genus is distributed throughout the tropics and subtropics. The ants are very rare, and are rarely collected in the field, but they appear to be nesting in the leaf litter ...

'' ants, chlamydephorid slugs, and predaceous dung beetles of the genera ''

Sceliages ''Sceliages'', Westwood, ('σκέλος' = leg), is a sub-genus of the ''Scarabaeus'' dung beetles, and are obligate predators of spirostreptid, spirobolid and julid millipedes, having renounced the coprophagy for which they were named. The ...

'' and '' Deltochilum''. A large subfamily of

assassin bugs The Reduviidae are a large cosmopolitan family of the order Hemiptera (true bugs). Among the Hemiptera and together with the Nabidae almost all species are terrestrial ambush predators: most other predatory Hemiptera are aquatic. The main exam ...

, the Ectrichodiinae with over 600 species, has specialised in preying upon millipedes.

Parasites Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson ha ...

of millipedes include nematodes, phaeomyiid flies, and

acanthocephala Acanthocephala (Greek , ', thorn + , ', head) is a phylum of parasitic worms known as acanthocephalans, thorny-headed worms, or spiny-headed worms, characterized by the presence of an eversible proboscis, armed with spines, which it uses to p ...

ns. Nearly 30 fungal species of the order Laboulbeniales have been found growing externally on millipedes, but some species may be

commensal Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit fro ...

rather than parasitic.

Defence mechanisms

Due to their lack of speed and their inability to bite or sting, millipedes' primary

defence mechanism In psychoanalytic theory, a defence mechanism (American English: defense mechanism), is an unconscious psychological operation that functions to protect a person from anxiety-producing thoughts and feelings related to internal conflicts and o ...

is to curl into a tight coil – protecting their delicate legs inside an armoured exoskeleton. Many species also emit various foul-smelling liquid secretions through microscopic holes called ozopores (the openings of "odoriferous" or "repugnatorial glands"), along the sides of their bodies as a secondary defence. Among the many irritant and toxic chemicals found in these secretions are

alkaloid Alkaloids are a class of basic, naturally occurring organic compounds that contain at least one nitrogen atom. This group also includes some related compounds with neutral and even weakly acidic properties. Some synthetic compounds of similar ...

benzoquinone Benzoquinone (C6H4O2) is a quinone with a single benzene ring. There are 2 (out of 3 hypothetical) benzoquinones: * 1,4-Benzoquinone, most commonly, right image (also ''para''-benzoquinone, ''p''-benzoquinone, ''para''-quinone, or just quinone) * 1 ...

phenols In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of one or more hydroxyl groups (— O H) bonded directly to an aromatic hydrocarbon group. The simplest is phenol, . Phenolic compounds are ...

terpenoid The terpenoids, also known as isoprenoids, are a class of naturally occurring organic chemicals derived from the 5-carbon compound isoprene and its derivatives called terpenes, diterpenes, etc. While sometimes used interchangeably with "terpenes" ...

s, and hydrogen cyanide. Some of these substances are caustic and can burn the exoskeleton of

ant Ants are eusocial insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from vespoid wasp ancestors in the Cretaceous period. More than 13,800 of an estimated total of ...

s and other insect predators, and the skin and eyes of larger predators. Primates such as

capuchin monkey The capuchin monkeys () are New World monkeys of the subfamily Cebinae. They are readily identified as the " organ grinder" monkey, and have been used in many movies and television shows. The range of capuchin monkeys includes some tropical fores ...

s and

lemur Lemurs ( ) (from Latin ''lemures'' – ghosts or spirits) are wet-nosed primates of the superfamily Lemuroidea (), divided into 8 families and consisting of 15 genera and around 100 existing species. They are endemic to the island of Madagas ...

s have been observed intentionally irritating millipedes in order to rub the chemicals on themselves to repel

mosquito Mosquitoes (or mosquitos) are members of a group of almost 3,600 species of small flies within the family Culicidae (from the Latin ''culex'' meaning " gnat"). The word "mosquito" (formed by ''mosca'' and diminutive ''-ito'') is Spanish for "li ...

es. Some of these defensive compounds also show antifungal activity. The bristly millipedes (order Polyxenida) lack both an armoured exoskeleton and odiferous glands, and instead are covered in numerous bristles that in at least one species, '' Polyxenus fasciculatus'', detach and entangle ants.

Other inter-species interactions

Some millipedes form mutualistic relationships with organisms of other species, in which both species benefit from the interaction, or commensal relationships, in which only one species benefits while the other is unaffected. Several species form close relationships with ants, a relationship known as

myrmecophily Myrmecophily ( , ) is the term applied to positive interspecies associations between ants and a variety of other organisms, such as plants, other arthropods, and fungi. Myrmecophily refers to mutualistic associations with ants, though in its m ...

, especially within the family

Pyrgodesmidae Pyrgodesmidae is a family of flat-backed millipedes in the order Polydesmida. The family contains over 200 species distributed in tropics around the world. Some species are found only in ant colonies, and are considered obligate myrmecophiles ...

(Polydesmida), which contains "obligate myrmecophiles", species which have only been found in ant colonies. More species are "facultative myrmecophiles", non-exclusively associated with ants, including many species of Polyxenida that have been found in ant nests around the world. Many millipede species have commensal relationships with

mite Mites are small arachnids (eight-legged arthropods). Mites span two large orders of arachnids, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari, but genetic analysis does not show clear e ...

s of the orders

Mesostigmata Mesostigmata is an order of mites belonging to the Parasitiformes. They are by far the largest group of Parasitiformes, with over 8,000 species in 130 families. Mesostigmata includes parasitic as well as free-living and predatory forms. They can ...

and Astigmata. Many of these mites are believed to be phoretic rather than parasitic, which means that they use the millipede host as a means of dispersal. A novel interaction between millipedes and mosses was described in 2011, in which individuals of the newly discovered ''

Psammodesmus bryophorus The moss millipede (''Psammodesmus bryophorus'') is a keeled millipede of the family Platyrhacidae native to Colombia. It was described in 2011, and with several species of symbiotic moss Mosses are small, non-vascular flowerless plants i ...

'' was found to have up to ten species living on its dorsal surface, in what may provide

camouflage Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the b ...

for the millipede and increased dispersal for the mosses.

Interactions with humans

Giant fire millipede (Aphistogoniulus corallipes) Mantadia

Millipedes generally have little impact on human economic or social well-being, especially in comparison with insects, although locally they can be a nuisance or agricultural pest. Millipedes do not bite, and their defensive secretions are mostly harmless to humans — usually causing only minor discolouration on the skin — but the secretions of some tropical species may cause pain, itching, local

erythema Erythema (from the Greek , meaning red) is redness of the skin or mucous membranes, caused by hyperemia (increased blood flow) in superficial capillaries. It occurs with any skin injury, infection, or inflammation. Examples of erythema not asso ...

, edema, blisters,

eczema Dermatitis is inflammation of the skin, typically characterized by itchiness, redness and a rash. In cases of short duration, there may be small blisters, while in long-term cases the skin may become thickened. The area of skin involved can ...

, and occasionally cracked skin. Eye exposures to these secretions causes general irritation and potentially more severe effects such as

conjunctivitis Conjunctivitis, also known as pink eye, is inflammation of the outermost layer of the white part of the eye and the inner surface of the eyelid. It makes the eye appear pink or reddish. Pain, burning, scratchiness, or itchiness may occur. The ...

and

keratitis Keratitis is a condition in which the eye's cornea, the clear dome on the front surface of the eye, becomes inflamed. The condition is often marked by moderate to intense pain and usually involves any of the following symptoms: pain, impaired e ...

. This is called

millipede burn Millipede burns are a cutaneous condition caused by certain millipedes that secrete a toxic liquid that causes a brownish pigmentation and/or burns when it comes into contact with the skin. Some millipedes produce quinones in their defensive secr ...

First aid First aid is the first and immediate assistance given to any person with either a minor or serious illness or injury, with care provided to preserve life, prevent the condition from worsening, or to promote recovery. It includes initial in ...

consists of flushing the area thoroughly with water; further treatment is aimed at relieving the local effects. Spotted snake millipede Blaniulus guttulatus

Spotted snake millipede Blaniulus guttulatus

Some millipedes are considered household pests, including '' Xenobolus carnifex'' which can infest thatched roofs in India, and ''

Ommatoiulus moreleti ''Ommatoiulus moreleti'' (spelt ''moreletii'' in older publications), commonly known as the Portuguese millipede, is a herbivorous millipede native to the western Iberian Peninsula where it shares its range with other ''Ommatoiulus'' species. Fro ...

'', which periodically invades homes in Australia. Other species exhibit periodical swarming behaviour, which can result in home invasions, crop damage, and train delays when the tracks become slippery with the crushed remains of hundreds of millipedes. Some millipedes can cause significant damage to crops: the spotted snake millipede (''Blaniulus guttulatus'') is a noted pest of sugar beets and other root crops, and as a result is one of the few millipedes with a common name. Some of the larger millipedes in the orders Spirobolida, Spirostreptida, and Sphaerotheriida are popular as pets. Some species commonly sold or kept include species of '' Archispirostreptus'', '' Aphistogoniulus'', ''

Narceus ''Narceus'' is a genus of large cylindrical millipedes of the family Spirobolidae native to eastern North America. The genus comprises three or four species, two of which are endemic to Florida, and the remainder forming a species complex. The ...

'', and '' Orthoporus''. Flat millipede

Millipedes appear in

folklore Folklore is shared by a particular group of people; it encompasses the traditions common to that culture, subculture or group. This includes oral traditions such as tales, legends, proverbs and jokes. They include material culture, ranging ...

and

traditional medicine Traditional medicine (also known as indigenous medicine or folk medicine) comprises medical aspects of traditional knowledge that developed over generations within the folk beliefs of various societies, including indigenous peoples, before the ...

around the world. Some cultures associate millipede activity with coming rains. In Zambia, smashed millipede pulp is used to treat wounds, and the

Bafia people The Bafia (Baepak) people are a central African ethnic group that inhabit the Mbam and Sanaga River regions in the Centre Region of Cameroon. They are culturally related to the Bamum and Tikar people. Names A Bafia father will give his child ...

of Cameroon use millipede juice to treat earache. In certain Himalayan

Bhotiya Bhotiya or Bhot ( ne, भोटिया, ) are groups of ethno-linguistically related Tibetan people living in the Transhimalayan region that divides India from Tibet. The word ''Bhotiya'' comes from the classical Tibetan name for Tibet, , . ...

tribes, dry millipede smoke is used to treat

haemorrhoid Hemorrhoids (or haemorrhoids), also known as piles, are vascular structures in the anal canal. In their normal state, they are cushions that help with stool control. They become a disease when swollen or inflamed; the unqualified term ''hem ...

s. Native people in

Malaysia Malaysia ( ; ) is a country in Southeast Asia. The federation, federal constitutional monarchy consists of States and federal territories of Malaysia, thirteen states and three federal territories, separated by the South China Sea into two r ...

use millipede secretions in poison-tipped arrows. The secretions of ''Spirobolus bungii'' have been observed to inhibit division of human cancer cells. The only recorded usage of millipedes as food by humans comes from the Bobo people of

Burkina Faso Burkina Faso (, ; , ff, 𞤄𞤵𞤪𞤳𞤭𞤲𞤢 𞤊𞤢𞤧𞤮, italic=no) is a landlocked country in West Africa with an area of , bordered by Mali to the northwest, Niger to the northeast, Benin to the southeast, Togo and Ghana to ...

West Africa West Africa or Western Africa is the westernmost region of Africa. The United Nations defines Western Africa as the 16 countries of Benin, Burkina Faso, Cape Verde, The Gambia, Ghana, Guinea, Guinea-Bissau, Ivory Coast, Liberia, Mali, M ...

, who consume boiled, dried millipedes belonging to the families Gomphodesmidae and Spirostreptidae to which they add tomato sauce. Millipedes have also inspired and played roles in scientific research. In 1963, a walking vehicle with 36 legs was designed, said to have been inspired by a study of millipede locomotion. Experimental robots have had the same inspiration, in particular when heavy loads are needed to be carried in tight areas involving turns and curves. In biology, some authors have advocated millipedes as model organisms for the study of arthropod physiology and the developmental processes controlling the number and shape of body segments. Similar to

vermicompost Vermicompost (vermi-compost) is the product of the decomposition process using various species of worms, usually red wigglers, white worms, and other earthworms, to create a mixture of decomposing vegetable or food waste, bedding materials, and ...

, millipedes can be used to convert plant matter into compost in what has been named millicomposting, which improves the quality of the compost.Millicompost: an alternate biocompost for forest nurseries
/ref>

References

External links

Milli-PEET: The Class Diplopoda
– The Field Museum, Chicago

Diplopoda: Guide to New Zealand Soil Invertebrates
– Massey University

British Myriapod & Isopod Group
{{DEFAULTSORT:Millipede Detritivores Wenlock first appearances Extant Silurian first appearances Myriapods Taxa named by Henri Marie Ducrotay de Blainville