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An earthworm is a terrestrial invertebrate that belongs to the phylum
Annelida
Annelida
. They exhibit a tube-within-a-tube
body plan A body plan, ''Bauplan'' (German plural ''Baupläne''), or ground plan is a set of morphological features common to many members of a phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ) ...
, are externally segmented with corresponding internal segmentation, and usually have
setae 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 Invertebrates Annelid setae are stiff bristles present on the body. Th ...

setae
on all segments. They occur worldwide where soil, water, and temperature allow. Earthworms are commonly found in
soil Surface-water- gley developed in glacial till, Northern Ireland.">Northern_Ireland.html" ;"title="glacial till, Northern Ireland">glacial till, Northern Ireland. Soil is a mixture of organic matter, minerals, gases, liquids, and organisms tha ...

soil
, eating a wide variety of organic matter. This organic matter includes plant matter, living
protozoa Protozoa (singular protozoon or protozoan, plural protozoa or protozoans) is an informal term for a group of Unicellular organism, single-celled eukaryotes, either free-living or Parasitism, parasitic, that feed on organic matter such as other mi ...

protozoa
,
rotifers The rotifers (, from Latin ''wikt:rota#Latin, rota'' "wheel" and ''wikt:-fer#Latin, -fer'' "bearing"), commonly called wheel animals or wheel animalcules, make up a phylum (Rotifera ) of microscopic and near-microscopic Coelom#Pseudocoelomates, p ...
,
nematodes The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the valu ...
,
bacteria Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typ ...

bacteria
,
fungi A fungus (plural The plural (sometimes abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters, or words taken from the full ...

fungi
, and other microorganisms. An earthworm's digestive system runs the length of its body. It respires through its skin. It has a double transport system made of coelomic fluid that moves within the fluid-filled
coelom The coelom (or celom) is the main body cavity A body cavity is any space or compartment, or potential space Potential generally refers to a currently unrealized ability. The term is used in a wide variety of fields, from physics to the social ...
and a simple, closed circulatory system. It has a
central Central is an adjective usually referring to being in the center (disambiguation), center of some place or (mathematical) object. Central may also refer to: Directions and generalised locations * Central Africa, a region in the centre of Africa ...

central
and
peripheral nervous system The peripheral nervous system (PNS) is one of two components that make up the nervous system In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, ...
. Its central nervous system consists of two
ganglia A ganglion is a group of neuron cell bodies in the peripheral nervous system The peripheral nervous system (PNS) is one of two components that make up the nervous system In Biology, biology, the nervous system is a Complex system, high ...

ganglia
above the mouth, one on either side, connected to a nerve running along its length to
motor neurons A motor neuron (or motoneuron or efferent neuron) is a neuron A neuron or nerve cell is an electrically excitable cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * ...

motor neurons
and sensory cells in each segment. Large numbers of
chemoreceptors A chemoreceptor, also known as chemosensor, is a specialized sensory receptor Sensory neurons, also known as afferent neurons, are neurons in the nervous system In Biology, biology, the nervous system is a Complex system, highly complex ...
concentrate near its mouth. Circumferential and longitudinal muscles edging each segment let the worm move. Similar sets of muscles line the gut, and their actions move digesting food toward the worm's anus. Earthworms are
hermaphrodite In reproductive biology Reproductive biology includes both sexual and asexual reproduction. Reproductive biology includes a wide number of fields: * Reproductive systems * Endocrinology Endocrinology (from '' endocrine'' + '' -ology'') is a b ...

hermaphrodite
s: each carries male and female sex organs. As invertebrates, they lack a true
skeleton A skeleton is a structural frame that supports an animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consu ...

skeleton
, but maintain their structure with fluid-filled coelom chambers that function as a hydrostatic skeleton. "Earthworm" is the common name for the largest members of
Oligochaeta Oligochaeta () is a subclass of animals in the phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical cate ...

Oligochaeta
(which is a class or subclass depending on the author). In classical systems, they were in the order
Opisthopora Opisthopora is an order of mostly terrestrial worms. It is an order of the subclass Oligochaeta, which is distinguished by meganephridiostomal, male pores which open posteriorly to the last testicular segment. It includes the megadrile families o ...
, since the male pores opened posterior to the female pores, although the internal male segments are anterior to the female. Theoretical
cladistic Cladistics (; ) is an approach to Taxonomy (biology), biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically ...

cladistic
studies have placed them in the suborder
Lumbricina An earthworm is a terrestrial invertebrate that belongs to the phylum Annelida. They exhibit a tube-within-a-tube body plan, are externally segmented with corresponding internal segmentation, and usually have setae on all segments. They occur wor ...
of the order
Haplotaxida The Haplotaxida are one of two order (biology), orders within the annelid Class (biology), subclass Oligochaeta, the other being the Lumbriculida. No real common name exists, but they are simply referred to as haplotaxids. Given that the other c ...
, but this may soon change. Folk names for the earthworm include "dew-worm", "rainworm", "nightcrawler", and "angleworm" (from its use as
fishing bait Fishing bait is any substance used to attract and catch fish Fish are aquatic Aquatic means relating to water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical subs ...
). Larger terrestrial earthworms are also called
megadrile A megadrile is a kind of worm, a mostly terrestrial oligochaete Oligochaeta () is a subclass of animals in the phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, ...
s (translates to "big worms"), opposed to the
microdrile Microdriles (small worms The World Register of Marine Species (WoRMS) is a taxonomic database that aims to provide an authoritative and comprehensive list of names of marine organisms. Content The content of the registry is edited and maintained ...
s ("small worms") in the semiaquatic families
Tubificidae The Naididae (including the former family Tubificidae) are a family In human society, family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). ...
,
Lumbricidae The Lumbricidae are a family of earthworms. About 33 lumbricid species have become naturalized around the world, but the bulk of the species are in the Holarctic region: from Canada (e.g. ''Bimastos lawrenceae'' on Vancouver Island) and the Unit ...

Lumbricidae
, and
Enchytraeidae Enchytraeidae is a family of microdrile oligochaetes Oligochaeta () is a subclass of animals in the phylum Annelida, which is made up of many types of aquatic and terrestrial worm Worms are many different distantly related animals th ...

Enchytraeidae
. The megadriles are characterized by a distinct
clitellum 200 px, right The clitellum is a thickened gland A gland is a group of cells in an animal's body that synthesizes substances (such as hormone A hormone (from the Greek participle , "setting in motion") is any member of a class of signaling mo ...
(more extensive than that of microdriles) and a vascular system with true capillaries.


Anatomy


Form and function

Depending on the species, an adult earthworm can be from long and wide to long and over wide, but the typical ''
Lumbricus terrestris
Lumbricus terrestris
'' grows to about long. Probably the longest worm on confirmed records is '' Amynthas mekongianus'' that extends up to 3 m (10 ft) in the mud along the banks of the 4,350 km (2,703 mi)
Mekong River The Mekong or Mekong River is a trans-boundary river A transboundary river is a river that crosses at least one political border, either a border within a nation or an international boundary. Bangladesh has the highest number of these rive ...

Mekong River
in Southeast Asia. From front to back, the basic shape of the earthworm is a cylindrical tube-in-a-tube, divided into a series of segments (called metamerisms) that compartmentalize the body. Furrows are generally externally visible on the body demarking the segments; dorsal pores and
nephridiopore A nephridiopore is part of the nephridium, an excretory organ found in many organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Bio ...
s exude a fluid that moistens and protects the worm's surface, allowing it to breathe. Except for the mouth and anal segments, each segment carries bristlelike hairs called lateral
seta In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanis ...

seta
e used to anchor parts of the body during movement; species may have four pairs of setae on each segment or more than eight sometimes forming a complete circle of setae per segment. Special ventral setae are used to anchor mating earthworms by their penetration into the bodies of their mates. Generally, within a species, the number of segments found is consistent across specimens, and individuals are born with the number of segments they will have throughout their lives. The first body segment (segment number 1) features both the earthworm's mouth and, overhanging the mouth, a fleshy lobe called the
prostomium The prostomium (From Ancient Greek, meaning "before the mouth"; plural: prostomia; sometimes also called the "acron") is the Cephalization, cephalized first body segment in an annelid worm's body at the anterior end. It is in front of (but does no ...
, which seals the entrance when the worm is at rest, but is also used to feel and chemically sense the worm's surroundings. Some species of earthworm can even use the prehensile prostomium to grab and drag items such as grasses and leaves into their burrow. An adult earthworm develops a belt-shaped glandular swelling, called the
clitellum 200 px, right The clitellum is a thickened gland A gland is a group of cells in an animal's body that synthesizes substances (such as hormone A hormone (from the Greek participle , "setting in motion") is any member of a class of signaling mo ...
, which covers several segments toward the front part of the animal. This is part of the reproductive system and produces egg capsules. The posterior is most commonly cylindrical like the rest of the body, but depending on the species, it may also be quadrangular, octagonal, trapezoidal, or flattened. The last segment is called the
periproctThe periproct is the final body segment in annelid The annelids (Annelida , from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in th ...
; the earthworm's anus, a short vertical slit, is found on this segment. The exterior of an individual segment is a thin
cuticle A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non-homology (biology), homologous, differing in the ...
over the skin, commonly pigmented red to brown, which has specialized cells that secrete mucus over the cuticle to keep the body moist and ease movement through the soil. Under the skin is a layer of nerve tissue, and two layers of muscles—a thin outer layer of circular muscle, and a much thicker inner layer of longitudinal muscle. Interior to the muscle layer is a fluid-filled chamber called a
coelom The coelom (or celom) is the main body cavity A body cavity is any space or compartment, or potential space Potential generally refers to a currently unrealized ability. The term is used in a wide variety of fields, from physics to the social ...
that by its pressurization provides structure to the worm's boneless body. The segments are separated from each other by septa (the plural of "septum") which are perforated transverse walls, allowing the coelomic fluid to pass between segments. A pair of structures called
nephrostome The nephrostome is the funnel-like component of a metanephridium. It is always oriented towards the coelom. The nephrostome is covered from the inside with motile cilia, cilia, which push the water, metabolic wastes, unnecessary hormones and othe ...
s are located at the back of each septum; a nephric tubule leads from each nephrostome through the septum and into the following segment. This tubule then leads to the main body fluid filtering organ, the
nephridium The nephridium (plural ''nephridia'') is an invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This includes all animals apart fr ...
or metanephridium, which removes metabolic waste from the coelomic fluid and expels it through pores called nephridiopores on the worm's sides; usually, two nephridia (sometimes more) are found in most segments. At the centre of a worm is the
digestive tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organ (biology), organs of the digestive syst ...
, which runs straight through from mouth to anus without coiling, and is flanked above and below by blood vessels (the dorsal blood vessel and the ventral blood vessel as well as a subneural blood vessel) and the
ventral nerve cord The ventral nerve cord (VNC) is a major structure of the invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This includes all ani ...
, and is surrounded in each segment by a pair of pallial blood vessels that connect the dorsal to the subneural blood vessels. Many earthworms can eject coelomic fluid through pores in the back in response to stress; the Australian ''Didymogaster sylvaticus'' (known as the "blue squirter earthworm") can squirt fluid as high as .


Nervous system


Central nervous system

The CNS consists of a bilobed
brain A brain is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tis ...

brain
(cerebral
ganglia A ganglion is a group of neuron cell bodies in the peripheral nervous system The peripheral nervous system (PNS) is one of two components that make up the nervous system In biology Biology is the natural science that studies li ...

ganglia
, or supra-pharyngeal ganglion), sub-pharyngeal ganglia, circum-pharyngeal connectives and a
ventral nerve cord The ventral nerve cord (VNC) is a major structure of the invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This includes all ani ...
. Earthworms' brains consist of a pair of pear-shaped cerebral ganglia. These are located in the dorsal side of the alimentary canal in the third segment, in a groove between the
buccal cavity Buccal may refer to: * Buccal, or buccal cavity, an oral body cavity (mouth In animal anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an org ...
and
pharynx The pharynx (plural: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea – the tubes going down to the stomach and the lungs. It is found in vertebrates and invertebrates, thou ...

pharynx
. A pair of circum-pharyngeal connectives from the brain encircle the pharynx and then connect with a pair of sub-pharyngeal ganglia located below the pharynx in the fourth segment. This arrangement means the brain, sub-pharyngeal ganglia and the circum-pharyngeal connectives form a nerve ring around the pharynx. The ventral nerve cord (formed by nerve cells and nerve fibers) begins at the sub-pharyngeal ganglia and extends below the alimentary canal to the most posterior body segment. The ventral nerve cord has a swelling, or ganglion, in each segment, i.e. a segmental ganglion, which occurs from the fifth to the last segment of the body. There are also three giant
axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences Despite the various English dialects Dialect The term dialect (from Latin , , from the Ancient Greek word , , "discourse", from ...
s, one medial giant axon (MGA) and two lateral giant axons (LGAs) on the mid-dorsal side of the ventral nerve cord. The MGA is 0.07 mm in diameter and transmits in an anterior-posterior direction at a rate of 32.2 m/s. The LGAs are slightly narrower at 0.05 mm in diameter and transmit in a posterior-anterior direction at 12.6 m/s. The two LGAs are connected at regular intervals along the body and are therefore considered one giant axon.


Peripheral nervous system

*Eight to ten nerves arise from the cerebral ganglia to supply the
prostomium The prostomium (From Ancient Greek, meaning "before the mouth"; plural: prostomia; sometimes also called the "acron") is the Cephalization, cephalized first body segment in an annelid worm's body at the anterior end. It is in front of (but does no ...
, buccal chamber and
pharynx The pharynx (plural: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea – the tubes going down to the stomach and the lungs. It is found in vertebrates and invertebrates, thou ...

pharynx
. *Three pairs of nerves arise from the subpharyangeal ganglia to supply the 2nd, 3rd and 4th segment. *Three pairs of nerves extend from each segmental ganglion to supply various structures of the segment. The sympathetic nervous system consists of nerve plexuses in the epidermis and alimentary canal. (A plexus is a web of connected nerve cells.) The nerves that run along the body wall pass between the outer circular and inner longitudinal muscle layers of the wall. They give off branches that form the intermuscular plexus and the subepidermal plexus. These nerves connect with the cricopharyngeal connective.


Movement

On the surface, crawling speed varies both within and among individuals. Earthworms crawl faster primarily by taking longer "strides" and a greater frequency of strides. Larger ''
Lumbricus terrestris
Lumbricus terrestris
'' worms crawl at a greater absolute speed than smaller worms. They achieve this by taking slightly longer strides but with slightly lower stride frequencies. Touching an earthworm, which causes a "pressure" response as well as (often) a response to the dehydrating quality of the salt on human skin (toxic to earthworms), stimulates the subepidermal nerve plexus which connects to the intermuscular plexus and causes the longitudinal muscles to contract. This causes the writhing movements observed when a human picks up an earthworm. This behaviour is a
reflex In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanism ...

reflex
and does not require the CNS; it occurs even if the nerve cord is removed. Each segment of the earthworm has its own nerve plexus. The plexus of one segment is not connected directly to that of adjacent segments. The nerve cord is required to connect the nervous systems of the segments. The giant axons carry the fastest signals along the nerve cord. These are emergency signals that initiate reflex escape behaviours. The larger dorsal giant axon conducts signals the fastest, from the rear to the front of the animal. If the rear of the worm is touched, a signal is rapidly sent forwards causing the longitudinal muscles in each segment to contract. This causes the worm to shorten very quickly as an attempt to escape from a predator or other potential threat. The two medial giant axons connect with each other and send signals from the front to the rear. Stimulation of these causes the earthworm to very quickly retreat (perhaps contracting into its burrow to escape a bird). The presence of a nervous system is essential for an animal to be able to experience
nociception Nociception (also nocioception, from Latin ''nocere'' 'to harm or hurt') is the Somatosensory system, sensory nervous system's process of encoding noxious stimuli. It deals with a series of events and processes required for an organism to receive a ...
or
pain Pain is a distressing feeling often caused by intense or damaging stimuli. The International Association for the Study of Pain The International Association for the Study of Pain (IASP) is an international learned society A learned societ ...
. However, other physiological capacities are also required such as opioid sensitivity and central modulation of responses by analgesics.
Enkephalin An enkephalin is a pentapeptide involved in regulating nociception Nociception (also nocioception, from Latin ''nocere'' 'to harm or hurt') is the Somatosensory system, sensory nervous system's process of encoding noxious stimuli. It deals with ...
and α-endorphin-like substances have been found in earthworms. Injections of
naloxone Naloxone, sold under the brand name Narcan among others, is a medication used to block the effects of opioids. It is commonly used to counter decreased breathing in opioid overdose. Naloxone may also be combined with an opioid (in the same pil ...

naloxone
(an opioid antagonist) inhibit the escape responses of earthworms. This indicates that opioid substances play a role in sensory modulation, similar to that found in many vertebrates.


Sensory reception


Photosensitivity

Earthworms do not have
eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light L ...

eye
s (although some worms do); however, they do have specialized photosensitive cells called "light cells of Hess". These photoreceptor cells have a central intracellular cavity ( phaosome) filled with
microvilli Microvilli (singular: microvillus) are microscopic cellular membrane protrusions that increase the surface area for diffusion and minimize any increase in volume, and are involved in a wide variety of functions, including absorption Absorption ma ...

microvilli
. As well as the microvilli, there are several sensory cilia in the phaosome which are structurally independent of the microvilli. The photoreceptors are distributed in most parts of the epidermis but are more concentrated on the back and sides of the worm. A relatively small number occurs on the ventral surface of the 1st segment. They are most numerous in the prostomium and reduce in density in the first three segments; they are very few in number past the third segment.


Epidermal receptor (Sense organ)

These receptors are abundant and distributed all over the
epidermis The epidermis is the outermost of the three layers that comprise the skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate Vertebrates () comprise all species of animal Animals (also calle ...

epidermis
. Each receptor shows a slightly elevated cuticle which covers a group of tall, slender and columnar receptor cells. These cells bear small hairlike processes at their outer ends and their inner ends are connected with nerve fibres. The epidermal receptors are tactile in function. They are also concerned with changes in temperature and respond to chemical stimuli. Earthworms are extremely sensitive to touch and mechanical vibration.


Buccal receptor (Sense organ)

These receptors are located only in the epithelium of the buccal chamber. These receptors are gustatory and olfactory (related to taste and smell). They also respond to chemical stimuli. (Chemoreceptor)


Digestive system

The gut of the earthworm is a straight tube which extends from the worm's mouth to its
anus The anus (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in ...

anus
. It is differentiated into an
alimentary canal The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system The human digestive system consists of the gastrointestinal tract The gastrointestinal tract, (GI tract, GIT, di ...
and associated glands which are embedded in the wall of the alimentary canal itself. The alimentary canal consists of a mouth, buccal cavity (generally running through the first one or two segments of the earthworm), pharynx (running generally about four segments in length), oesophagus, crop, gizzard (usually) and intestine. Food enters at the mouth. The
pharynx The pharynx (plural: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea – the tubes going down to the stomach and the lungs. It is found in vertebrates and invertebrates, thou ...

pharynx
acts as a suction pump; its muscular walls draw in food. In the pharynx, the pharyngeal glands secrete
mucus Mucus ( ) is a slippery aqueous secretion produced by, and covering, mucous membrane A mucous membrane or mucosa is a biological membrane, membrane that lines various cavities in the body and covers the surface of internal organs. It consists o ...
. Food moves into the
esophagus The esophagus (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of variety (linguistics), varieties of the English language native to the United State ...

esophagus
, where
calcium Calcium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

calcium
(from the blood and ingested from previous meals) is pumped in to maintain proper blood calcium levels in the blood and food . From there the food passes into the crop and gizzard. In the
gizzard The gizzard, also referred to as the ventriculus, gastric mill, and gigerium, is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rel ...

gizzard
, strong muscular contractions grind the food with the help of mineral particles ingested along with the food. Once through the gizzard, food continues through the intestine for digestion. The intestine secretes
pepsin Pepsin is an endopeptidase that breaks down proteins into smaller peptides. It is produced in the gastric chief cells of the stomach lining and is one of the main digestive enzymes in the digestive systems of humans and many other animals, where ...

pepsin
to digest proteins,
amylase An amylase () is an enzyme Enzymes () are protein Proteins are large s and s that comprise one or more long chains of . Proteins perform a vast array of functions within organisms, including , , , providing and , and from one lo ...
to digest polysaccharides,
cellulase Cellulase is any of several enzymes Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, a ...
to digest cellulose, and lipase to digest fats. Earthworms use, in addition to the digestive proteins, a class of surface active compounds called drilodefensins, which help digest plant material. Instead of being coiled like a mammalian intestine, in an earthworm's intestine a large mid-dorsal, tongue-like fold is present, called typhlosole which increases surface area to increase nutrient absorption by having many folds running along its length. The intestine has its own pair of muscle layers like the body, but in reverse order—an inner circular layer within an outer longitudinal layer.


Circulatory system

Earthworms have a dual circulatory system in which both the coelomic fluid and a closed circulatory system carry the food, waste, and respiratory gases. The closed circulatory system has five main blood vessels: the dorsal (top) vessel, which runs above the digestive tract; the ventral (bottom) vessel, which runs below the digestive tract; the subneural vessel, which runs below the ventral nerve cord; and two lateroneural vessels on either side of the nerve cord. The dorsal vessel is mainly a collecting structure in the intestinal region. It receives a pair commissural and dorsal intestines in each segment. The ventral vessel branches off to a pair of ventro-tegumentaries and ventro-intestinals in each segment. The subneural vessel also gives out a pair of commissurals running along the posterior surface of the septum. The pumping action on the dorsal vessel moves the blood forward, while the other four longitudinal vessels carry the blood rearward. In segments seven through eleven, a pair of aortic arches ring the coelom and acts as hearts, pumping the blood to the ventral vessel that acts as the aorta. The blood consists of ameboid cells and haemoglobin dissolved in the plasma. The second circulatory system derives from the cells of the digestive system that line the coelom. As the digestive cells become full, they release non-living cells of fat into the fluid-filled coelom, where they float freely but can pass through the walls separating each segment, moving food to other parts and assist in wound healing.


Excretory system

The excretory system contains a pair of
nephridia The nephridium (plural ''nephridia'') is an invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This includes all animals apart fr ...
in every segment, except for the first three and the last ones. The three types of nephridia are: integumentary, septal, and pharyngeal. The integumentary nephridia lie attached to the inner side of the body wall in all segments except the first two. The septal nephridia are attached to both sides of the septa behind the 15th segment. The pharyngeal nephridia are attached to the fourth, fifth and sixth segments. The waste in the coelom fluid from a forward segment is drawn in by the beating of
cilia The cilium (; the plural is cilia) is an organelle In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, ...
of the
nephrostome The nephrostome is the funnel-like component of a metanephridium. It is always oriented towards the coelom. The nephrostome is covered from the inside with motile cilia, cilia, which push the water, metabolic wastes, unnecessary hormones and othe ...
. From there it is carried through the septum (wall) via a tube which forms a series of loops entwined by blood capillaries that also transfer waste into the tubule of the nephrostome. The excretory wastes are then finally discharged through a pore on the worm's side.


Respiration

Earthworms have no special respiratory organs. Gases are exchanged through the moist skin and capillaries, where the oxygen is picked up by the haemoglobin dissolved in the blood plasma and carbon dioxide is released. Water, as well as salts, can also be moved through the skin by active transport.


Life and physiology

At birth, earthworms emerge small but fully formed, lacking only their sex structures which develop in about 60 to 90 days. They attain full size in about one year. Scientists predict that the average lifespan under field conditions is four to eight years, while most garden varieties live only one to two years.


Reproduction

Several common earthworm species are mostly
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 development ...
, meaning that growth and development of
embryo An embryo is the early stage of development of a multicellular organism A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms ar ...

embryo
s happens without
fertilization Fertilisation or fertilization (see American and British English spelling differences#-ise.2C -ize .28-isation.2C -ization.29, spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes ...

fertilization
. Among earthworms, parthenogenesis arose from sexual relatives many times. Parthenogenesis in some ''Aporrectodea trapezoides'' lineages arose 6.4 to 1.1 million years ago from sexual ancestors. A few species exhibit pseudogamous parthogenesis, meaning that mating is necessary to stimulate reproduction, even though no male genetic material passes to the offspring. Earthworm mating occurs on the surface, most often at night. Earthworms are
hermaphrodite In reproductive biology Reproductive biology includes both sexual and asexual reproduction. Reproductive biology includes a wide number of fields: * Reproductive systems * Endocrinology Endocrinology (from '' endocrine'' + '' -ology'') is a b ...

hermaphrodite
s; that is, they have both male and female sexual organs. The sexual organs are located in segments 9 to 15. Earthworms have one or two pairs of testes contained within sacs. The two or four pairs of
seminal vesicle The seminal vesicles (also called vesicular glands, or seminal glands) are a pair of two convoluted tubular glands that lie behind the urinary bladder The urinary bladder, or simply bladder, is a hollow muscular MUSCULAR (DS-200B), located i ...
s produce, store and release the sperm via the male pores. Ovaries and oviducts in segment 13 release eggs via female pores on segment 14, while sperm is expelled from segment 15. One or more pairs of
spermatheca The spermatheca (pronounced plural: spermathecae ), also called receptaculum seminis (plural: receptacula seminis), is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar f ...
e are present in segments 9 and 10 (depending on the species) which are internal sacs that receive and store sperm from the other worm during copulation. As a result, segment 15 of one worm exudes sperm into segments 9 and 10 with its storage vesicles of its mate. Some species use external
spermatophore A spermatophore or sperm ampulla is a capsule or mass containing spermatozoa A spermatozoon (pronounced , alternate spelling spermatozoön; plural spermatozoa; from grc, σπέρμα ("seed") and grc, ζῷον ("living being")) is a motile spe ...
s for sperm transfer. In ''Hormogaster samnitica'' and ''Hormogaster elisae''
transcriptome The transcriptome is the set of all RNA Ribonucleic acid (RNA) is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, ...
DNA libraries were sequenced and two sex
pheromone A pheromone (from Ancient Greek Ancient Greek includes the forms of the Greek language Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), generally referred to by speakers simply as Greek (, ...

pheromone
s, Attractin and Temptin, were detected in all tissue samples of both
species In biology, a species is the basic unit of biological classification, 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 individu ...

species
. Sex pheromones are probably important in earthworms because they live in an environment where chemical signaling may play a crucial role in attracting a partner and in facilitating outcrossing. Outcrossing would provide the benefit of masking the expression of deleterious recessive mutations in progeny (see
Complementation A complement is often something that completes something else, or at least adds to it in some useful way. Thus it may be: * Complement (linguistics), a word or phrase having a particular syntactic role ** Subject complement, a word or phrase addi ...
).
Copulation Sexual intercourse (or coitus or copulation) is a sexual activity typically involving the insertion and Pelvic thrust, thrusting of the penis into the vagina for Sexual stimulation, sexual pleasure, sexual reproduction, reproduction, or both.S ...
and
reproduction Reproduction (or procreation or breeding) is the biological process Biological processes are those processes that are vital for an organism In biology, an organism () is any organic, life, living system that functions as an indivi ...

reproduction
are separate processes in earthworms. The mating pair overlap front ends ventrally and each exchanges sperm with the other. The
clitellum 200 px, right The clitellum is a thickened gland A gland is a group of cells in an animal's body that synthesizes substances (such as hormone A hormone (from the Greek participle , "setting in motion") is any member of a class of signaling mo ...
becomes very reddish to pinkish in colour. Sometime after copulation, long after the worms have separated, the clitellum (behind the spermathecae) secretes material which forms a ring around the worm. The worm then backs out of the ring, and as it does so, it injects its own eggs and the other worm's sperm into it. Thus each worm becomes the genetic father of some of their offspring and the genetic mother of the rest. As the worm slips out of the ring, the ends of the cocoon seal to form a vaguely onion-shaped incubator (
cocoon Cocoon may refer to: *Cocoon (silk), a pupal casing made by moth caterpillars and other insect larvae *Apache Cocoon, web development software *Cocoon (film), ''Cocoon'' (film), a 1985 science fiction-fantasy film **''Cocoon: The Return'', 1988 sequ ...

cocoon
) in which the embryonic worms develop. Hence fertilization is external. The cocoon is then deposited in the soil.After three weeks about 2 to 20 young ones hatch with an average of 4. Development is direct i.e.without formation of any larva.


Locomotion

Earthworms travel underground by the means of waves of muscular contractions which alternately shorten and lengthen the body (
peristalsis Peristalsis is a radially symmetrical Symmetry in biology refers to the symmetry observed in organisms, including plants, animals, fungi, and bacteria. External symmetry can be easily seen by just looking at an organism. For example, take ...

peristalsis
). The shortened part is anchored to the surrounding soil by tiny clawlike bristles (
seta In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanis ...

seta
e) set along its segmented length. In all the body segments except the first, last and clitellum, there is a ring of S-shaped setae embedded in the epidermal pit of each segment (perichaetine). The whole burrowing process is aided by the secretion of lubricating mucus. As a result of their movement through their lubricated tunnels, worms can make gurgling noises underground when disturbed. Earthworms move through soil by expanding crevices with force; when forces are measured according to body weight, hatchlings can push 500 times their own body weight whereas large adults can push only 10 times their own body weight.


Regeneration

Earthworms have the ability to regenerate lost segments, but this ability varies between species and depends on the extent of the damage. Stephenson (1930) devoted a chapter of his monograph to this topic, while G. E. Gates spent 20 years studying regeneration in a variety of species, but "because little interest was shown", Gates (1972) published only a few of his findings that, nevertheless, show it is theoretically possible to grow two whole worms from a bisected specimen in certain species. Gates's reports included: *''
Eisenia fetida ''Eisenia fetida'' (older spelling: foetida), known under various common names such as manure worm, redworm, brandling worm, panfish worm, trout worm, tiger worm, red wiggler worm, etc., is a species of earthworm An earthworm is a terrestrial ...
'' ( Savigny, 1826) with head regeneration, in an anterior direction, possible at each intersegmental level back to and including 23/24, while tails were regenerated at any levels behind 20/21; thus two worms may grow from one. *'''' (
Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his Nobility#Ennoblement, ennoblement as Carl von Linné#Blunt, Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomi ...

Linnaeus
,
1758 Events January–March * January 1 January 1 or 1 January is the first day of the year in the . There are 364 days remaining until the end of the year (365 in s). This day is known as since the day marks the beginning of the ...
)
replacing anterior segments from as far back as 13/14 and 16/17 but tail regeneration was never found. *'' Perionyx excavatus'' (Perrier, 1872) readily regenerated lost parts of the body, in an anterior direction from as far back as 17/18, and in a posterior direction as far forward as 20/21. *'' Lampito mauritii'' (Kinberg, 1867) with regeneration in anterior direction at all levels back to 25/26 and tail regeneration from 30/31; head regeneration was sometimes believed to be caused by internal amputation resulting from '''' sp. larval infestation. *'''' (Hoffmeister, 1845) also has prodigious regenerative capacity with 'head' regeneration from as far back as 40/41. An unidentified Tasmanian earthworm shown growing a replacement head has been reported.


Taxonomy and distribution

Within the world of taxonomy, the stable 'Classical System' of Michaelsen (1900) and Stephenson (1930) was gradually eroded by the controversy over how to classify earthworms, such that Fender and McKey-Fender (1990) went so far as to say, "The family-level classification of the Megascolecidae, megascolecid earthworms is in chaos." Over the years, many scientists have developed their own classification systems for earthworms, which led to confusion, and these systems have been and still continue to be revised and updated. The classification system used here which was developed by Blakemore (2000), is a modern reversion to the Classical System that is historically proven and widely accepted. Categorization of a
megadrile A megadrile is a kind of worm, a mostly terrestrial oligochaete Oligochaeta () is a subclass of animals in the phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, ...
earthworm into one of its taxonomic families under suborders Lumbricidae, Lumbricina and Moniligastridae, Moniligastrida is based on such features as the makeup of the clitellum, the location and disposition of the sex features (pores, prostatic glands, etc.), number of gizzards, and body shape. Currently, over 6,000 species of terrestrial earthworms are named, as provided in a species name database, but the number of synonyms is unknown. The families, with their known distributions or origins: * Acanthodrilidae * Ailoscolecidae – the Pyrenees and the southeast USA * Almidae – tropical equatorial (South America, Africa, Indo-Asia) * Benhamiinae – Ethiopian, Neotropical (a possible subfamily of Octochaetidae) * Criodrilidae – southwestern Palaearctic: Europe, Middle East, Russia and Siberia to Pacific coast; Japan (Biwadrilus); mainly aquatic * Diplocardiinae/-idae – Gondwanan or Laurasian? (a subfamily of Acanthodrilidae) *
Enchytraeidae Enchytraeidae is a family of microdrile oligochaetes Oligochaeta () is a subclass of animals in the phylum Annelida, which is made up of many types of aquatic and terrestrial worm Worms are many different distantly related animals th ...

Enchytraeidae
– cosmopolitan but uncommon in tropics (usually classed with Microdriles) * Eudrilidae – Tropical Africa south of the Sahara * Exxidae – Neotropical: Central America and the Caribbean * Glossoscolecidae – Neotropical: Central and South America, Caribbean * Haplotaxidae – cosmopolitan distribution (usually classed with Microdriles) * Hormogastridae – Mediterranean * Kynotidae – Malagasian: Madagascar *
Lumbricidae The Lumbricidae are a family of earthworms. About 33 lumbricid species have become naturalized around the world, but the bulk of the species are in the Holarctic region: from Canada (e.g. ''Bimastos lawrenceae'' on Vancouver Island) and the Unit ...

Lumbricidae
– Holarctic: North America, Europe, Middle East, Central Asia to Japan * Lutodrilidae – Louisiana the southeast USA * Megascolecidae * Microchaetidae – Terrestrial in Africa especially South African grasslands * Moniligastridae – Oriental and Indian subregion * Ocnerodrilidae – Neotropics, Africa; India * Octochaetidae – Australasian, Indian, Oriental, Ethiopian, Neotropical * Octochaetinae – Australasian, Indian, Oriental (subfamily if Benhamiinae is accepted) * Sparganophilidae – Nearctic, Neotropical: North and Central America * Tumakidae – Colombia, South America


As an invasive species

From a total of around 7,000 species, only about 150 species are widely distributed around the world. These are the peregrine or cosmopolitan earthworms.


Ecology

Earthworms are classified into three main ecophysiological categories: (1) leaf litter- or compost-dwelling worms that are nonburrowing, live at the soil-litter interface and eat decomposing organic matter (epigeic) e.g. ''Eisenia fetida''; (2) topsoil- or subsoil-dwelling worms that feed (on soil), burrow and cast within the soil, creating horizontal burrows in upper 10–30  cm of soil (endogeic); and (3) worms that construct permanent deep vertical burrows which they use to visit the surface to obtain plant material for food, such as leaves (anecic, meaning "reaching up"), e.g. ''Lumbricus terrestris''. Earthworm populations depend on both physical and chemical properties of the soil, such as temperature, moisture, pH, salts, aeration, and texture, as well as available food, and the ability of the species to reproduce and disperse. One of the most important environmental factors is , but earthworms vary in their preferences. Most favour neutral to slightly acidic soils. ''Lumbricus terrestris'' is still present in a pH of 5.4, ''Dendrobaena octaedra'' at a pH of 4.3 and some Megascolecidae are present in extremely acidic humic soils. Soil pH may also influence the numbers of worms that go into diapause. The more acidic the soil, the sooner worms go into diapause and the longer they remain in diapause at a pH of 6.4. Earthworms are preyed upon by many species of birds (e.g. robins, starlings, Thrush (bird), thrushes, gulls, crows), snakes, wood turtles, mammals (e.g. bears, boars, foxes, hedgehogs, pigs, mole (animal), moles) and invertebrates (e.g. ants, New Zealand flatworm, flatworms, ground beetles and other beetles, snails, spiders, and slugs). Earthworms have many internal parasites, including
protozoa Protozoa (singular protozoon or protozoan, plural protozoa or protozoans) is an informal term for a group of Unicellular organism, single-celled eukaryotes, either free-living or Parasitism, parasitic, that feed on organic matter such as other mi ...

protozoa
, platyhelminthes, and nematodes; they can be found in the worms' blood,
seminal vesicle The seminal vesicles (also called vesicular glands, or seminal glands) are a pair of two convoluted tubular glands that lie behind the urinary bladder The urinary bladder, or simply bladder, is a hollow muscular MUSCULAR (DS-200B), located i ...
s,
coelom The coelom (or celom) is the main body cavity A body cavity is any space or compartment, or potential space Potential generally refers to a currently unrealized ability. The term is used in a wide variety of fields, from physics to the social ...
, or intestine, or in their Pupa, cocoons. Nitrogenous fertilizers tend to create Soil pH, acidic conditions, which are fatal to the worms, and dead specimens are often found on the surface following the application of substances such as DDT, lime sulphur, and lead arsenate. In Australia, changes in farming practices such as the application of superphosphates on pastures and a switch from pastoral farming to Agronomy, arable farming had a devastating effect on populations of the giant Gippsland earthworm, leading to their classification as a protected species. Globally, certain earthworms populations have been devastated by deviation from organic production and the spraying of synthetic fertilizers and biocides, with at least three species now listed as extinct but many more endangered. Vermicomposting of all organic "wastes" and addition of this organic matter, preferably as a surface mulch, on a regular basis, will provide earthworms with their food and nutrient requirements, and will create the optimum conditions of temperature and moisture that will naturally stimulate their activity. This earthworm activity aerates and mixes the soil, and is conducive to mineralization of nutrients and their uptake by vegetation. Certain species of earthworm come to the surface and graze on the higher concentrations of organic matter present there, mixing it with the mineral soil. Because a high level of organic matter mixing is associated with soil fertility, an abundance of earthworms is generally considered beneficial by farmers and gardeners.NSW Department of Primary Industries
How earthworms can help your soil
/ref>Galveston County Master Gardener Association

/ref> As long ago as 1881 Charles Darwin wrote: "It may be doubted whether there are many other animals which have played so important a part in the history of the world, as have these lowly organized creatures." Also, while, as the name suggests, the main habitat of earthworms is in soil, they are not restricted to this habitat. The brandling worm ''
Eisenia fetida ''Eisenia fetida'' (older spelling: foetida), known under various common names such as manure worm, redworm, brandling worm, panfish worm, trout worm, tiger worm, red wiggler worm, etc., is a species of earthworm An earthworm is a terrestrial ...
'' lives in decaying plant matter and manure. ''Arctiostrotus vancouverensis'' from Vancouver Island and the Olympic Peninsula is generally found in decaying conifer logs. ''Aporrectodea limicola'', ''Sparganophilus'' spp., and several others are found in mud in streams. Some species are arboreal, some aquatic and some euryhaline (salt-water tolerant) and littoral (living on the sea-shore, e.g. ''Pontodrilus litoralis''). Even in the soil species, special habitats, such as soils derived from serpentine subgroup, serpentine, have an earthworm fauna of their own. Earthworms are environmental indicators of soil health. Earthworms feed on the decaying matter in the soil and analyzing the contents of their digestive tracts gives insight into the overall condition of the soil. The earthworm gut accumulates chemicals, including heavy metals such as cadmium, mercury, zinc, and copper. The population size of the earthworm indicates the quality of the soil as healthy soil would contain a larger number of earthworms.


Environmental impacts

The major benefits of earthworm activities to soil fertility for agriculture can be summarized as: * Biological: In many soils, earthworms play a major role in the conversion of large pieces of organic matter into rich humus, thus improving soil fertility. This is achieved by the worm's actions of pulling below the surface deposited organic matter such as leaf fall or manure, either for food or to plug its burrow. Once in the burrow, the worm will shred the leaf, partially digest it and mingle it with the earth. Worm casts (see bottom right) can contain 40 percent more humus than the top 9" (23 cm) of soil in which the worm is living. * Chemical: In addition to dead organic matter, the earthworm also ingests any other soil particles that are small enough—including sand grains up to 1/20 of an inch (1.25 mm)—into its gizzard, wherein those minute fragments of grit grind everything into a fine paste which is then digested in the intestine. When the worm excretes this in the form of casts, deposited on the surface or deeper in the soil, minerals and plant nutrients are changed to an accessible form for plants to use. Investigations in the United States show that fresh earthworm casts are five times richer in available nitrogen, seven times richer in available phosphates, and 11 times richer in available potassium than the surrounding upper 6 inches (150 mm) of soil. In conditions where humus is plentiful, the weight of casts produced may be greater than 4.5 kg (10 lb) per worm per year. * Physical: The earthworm's burrowing creates a multitude of channels through the soil and is of great value in maintaining the soil structure, enabling processes of aeration and drainage. Permaculture co-founder Bill Mollison points out that by sliding in their tunnels, earthworms "act as an innumerable army of pistons pumping air in and out of the soils on a 24-hour cycle (more rapidly at night)". Thus, the earthworm not only creates passages for air and water to traverse the soil, but also modifies the vital organic component that makes a soil healthy (see Bioturbation). Earthworms promote the formation of nutrient-rich casts (globules of soil, stable in soil mucus) that have high soil aggregation and soil fertility and quality. In podzol soils, earthworms can obliterate the characteristic banded appearance of the soil profile by mixing the organic (LFH), eluvial (E) and upper illuvial (B) horizons to create a single dark Ap horizon. Earthworms accelerate nutrient cycling in the soil-plant system through fragmentation & mixing of plant debris – physical grinding & chemical digestion. The earthworm's existence cannot be taken for granted. Dr. W. E. Shewell-Cooper observed "tremendous numerical differences between adjacent gardens", and worm populations are affected by a host of environmental factors, many of which can be influenced by good management practices on the part of the gardener or farmer. Darwin estimated that arable land contains up to 53,000 worms per acre (13/m2), but more recent research has produced figures suggesting that even poor soil may support 250,000/acre (62/m2), whilst rich fertile farmland may have up to 1,750,000/acre (432/m2), meaning that the weight of earthworms beneath a farmer's soil could be greater than that of the livestock upon its surface. Richly organic topsoil populations of earthworms are much higher – averaging 500 worms m−2 and up to 400 gm−2 – such that, for the 7 billion of us, each person alive today has support of 7 million earthworms. The ability to break down organic materials and excrete concentrated nutrients makes the earthworm a functional contributor in restoration projects. In response to ecosystem disturbances, some sites have utilized earthworms to prepare soil for the return of native flora. Research from the Station d'écologie de Lamto, Station d'écologie Tropicale de Lamto asserts that the earthworms positively influence the rate of macroaggregate formation, an important feature for soil structure. The stability of aggregates in response to water was also found to be improved when constructed by earthworms. Though not fully quantified yet, Greenhouse-gas emissions, Greenhouse gas emissions of earthworms likely contribute to global warming, especially since top-dwelling earthworms increase the speed of carbon cycles and have been spread by humans into many new geographies.


Economic impact

Various species of worms are used in vermiculture, the practice of feeding organic waste to earthworms to decompose food waste. These are usually ''
Eisenia fetida ''Eisenia fetida'' (older spelling: foetida), known under various common names such as manure worm, redworm, brandling worm, panfish worm, trout worm, tiger worm, red wiggler worm, etc., is a species of earthworm An earthworm is a terrestrial ...
'' (or its close relative ''Eisenia andrei'') or the Brandling worm, commonly known as the tiger worm or red wiggler. They are distinct from soil-dwelling earthworms. In the tropics, the African nightcrawler ''Eudrilus eugeniae'' and the Indian blue '' Perionyx excavatus'' are used. Earthworms are sold all over the world; the market is sizable. According to Doug Collicut, "In 1980, 370 million worms were exported from Canada, with a Canadian export value of $13 million and an American retail value of $54 million." Earthworms provide an excellent source of protein for fish, fowl and pigs but were also used traditionally for human consumption. Noke (worms), ''Noke'' is a culinary term used by the Māori people, Māori of New Zealand, and refers to earthworms which are considered delicacies for their chiefs.


See also

*Drilosphere, the part of the soil influenced by earthworm secretions and castings *''The Formation of Vegetable Mould through the Action of Worms'', an 1881 book by Charles Darwin *Soil life *Vermicompost *Vermifilter *Vermifilter toilet, Vermifilter Toilet *Worm charming


References


Further reading

* Edwards, Clive A., Bohlen, P.J. (Eds.) ''Biology and Ecology of Earthworms''. Springer, 2005. 3rd edition. * Edwards, Clive A. (Ed.) ''Earthworm Ecology''. Boca Raton: CRC Press, 2004. Second revised edition. * Lee, Keneth E. ''Earthworms: Their Ecology and Relationships with Soils and Land Use''. Academic Press. Sydney, 1985. * Stewart, Amy. ''The Earth Moved: On the Remarkable Achievements of Earthworms''. Chapel Hill, N.C.: Algonquin Books, 2004. {{Authority control Annelids Soil biology Invertebrate common names Paraphyletic groups lt:Sliekas