''Gordius'' is a genus of

worm Worms are many different distantly related bilateria, bilateral animals that typically have a long cylindrical tube-like body, no limb (anatomy), limbs, and usually no eyes. Worms vary in size from microscopic to over in length for marine ...

s in the phylum

Nematomorpha Nematomorpha (sometimes called Gordiacea, and commonly known as horsehair worms, hairsnakes, or Gordian worms) are a phylum of parasitoid animals superficially similar to nematode worms in morphology, hence the name. Most species range in size f ...

, the horsehair worms. It was formerly treated as the only genus in the family Gordiidae, but the genus '' Acutogordius'' is now considered as distinct.Bleidorn, C., et al. (2002)
Systematic relationships of Nematomorpha based on molecular and morphological data.
''Invertebrate Biology'' 121(4), 357-64. The genus is distributed worldwide except for

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...

, where no Nematomorpha have been recorded.Schmidt-Rhaesa, A. (2002)
Are the genera of Nematomorpha monophyletic taxa?
''Zoologica Scripta'' 31(2), 185-200.

Description

The adult worm is a free-living animal. It is hairlike, very long and very thin. It commonly grows over a meter long,Capinera, J. L
Horsehair Worms, Hairworms, Gordian Worms, Nematomorphs, ''Gordius'' spp. (Nematomorpha: Gordioidea).
EENY-117. Entomology and Nematology. Florida Cooperative Extension Service. University of Florida IFAS. Published 1999, revised 2005. with the record length held by a specimen of ''G. fulgur'' over two meters long,Schmidt-Rhaesa, A. and R. Ehrmann. (2001)
Horsehair worms (Nematomorpha) as parasites of praying mantids with a discussion of their life cycle.
''Zoologischer Anzeiger'' 240(2), 167-79. and may be only about one millimeter wide. It is reddish brown to black. Besides a blunt anterior end and a slightly widened posterior end, it is featureless to the naked eye. Microscopic features include a diagnostic character of the family, both ''Gordius'' and genus ''Acutogordius'', the postcloacal crescent of the male, a fold in the cuticle curving around the back side of the

cloaca A cloaca ( ), : cloacae ( or ), or vent, is the rear orifice that serves as the only opening for the digestive (rectum), reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles, birds, cartilagin ...

. At the front end of the body there is a white cap and a dark collar. At the posterior end there are tiny bristles, sometimes arranged in a row in front of the cloaca. Some species have a smooth body surface, and some may be slightly bumpy with flattened areoles. Most of these features are used in species identification, but are not very helpful, and it is difficult to tell species apart, in general. A thorough

taxonomy image:Hierarchical clustering diagram.png, 280px, Generalized scheme of taxonomy Taxonomy is a practice and science concerned with classification or categorization. Typically, there are two parts to it: the development of an underlying scheme o ...

of the genus will require a

scanning electron microscope A scanning electron microscope (SEM) is a type of electron microscope that produces images of a sample by scanning the surface with a focused beam of electrons. The electrons interact with atoms in the sample, producing various signals that ...

.Schmidt-Rhaesa, A. (2010)
Considerations on the genus ''Gordius'' (Nematomorpha, horsehair worms), with the description of seven new species.
''Zootaxa'' 2533, 1-35.

Biology

These worms can only live near water, because parts of their life cycle take place in it. The adult

overwinters Overwintering is the process by which some organisms pass through or wait out the winter season, or pass through that period of the year when "winter" conditions (cold or sub-zero temperatures, ice, snow, limited food supplies) make normal activi ...

in soil and debris and the female enters a water body such as a

swamp A swamp is a forested wetland.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p. Swamps are considered to be transition zones because both land and water play a role in ...

or a stream to lay eggs. A gelatinous string of eggs each about 50

micrometers The micrometre (Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a unit of length in the International System ...

long is released into the water. The female can produce a great many eggs, perhaps up to 27 million in its lifetime. Juveniles require a

host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places * Host, Pennsylvania, a village in Berks County * Host Island, in the Wilhelm Archipelago, Antarctica People * ...

in which to complete their development. Upon emergence from the egg the

larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

swims about until it is consumed by a host insect. Most ''Gordius'' worms are

parasites Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The en ...

beetle Beetles are insects that form the Taxonomic rank, order Coleoptera (), in the superorder Holometabola. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 40 ...

s. Other recorded hosts include

mantids Mantidae is one of the largest family (biology), families in the Order (biology), order of Mantodea, praying mantises, based on the type species ''Mantis religiosa''; most genera are tropical or subtropical. Historically, this was the only family ...

such as the

European mantis The European mantis (''Mantis religiosa'') is a large hemimetabolic insect in the Mantidae family, which is the largest family of the order Mantodea (mantises). Their common name praying mantis is derived from the distinctive posture of the firs ...

(''Mantis religiosa'') and '' Hierodula membranacea'', '' Idolomantis diabolica'', '' Sphodromantis viridis'', and '' Stagmatoptera praecaria''. Species have been observed in

caddisfly The caddisflies (order Trichoptera) are a group of insects with aquatic larvae and terrestrial adults. There are approximately 14,500 described species, most of which can be divided into the suborders Integripalpia and Annulipalpia on the basis ...

and

mosquito Mosquitoes, the Culicidae, are a Family (biology), family of small Diptera, flies consisting of 3,600 species. The word ''mosquito'' (formed by ''Musca (fly), mosca'' and diminutive ''-ito'') is Spanish and Portuguese for ''little fly''. Mos ...

larvae. Once ingested by the insect the worm larva penetrates the gut wall and develops in a

cyst A cyst is a closed sac, having a distinct envelope and division compared with the nearby tissue. Hence, it is a cluster of cells that have grouped together to form a sac (like the manner in which water molecules group together to form a bubb ...

in the tissue outside. It emerges as an adult worm in a few months. ''Gordius'' worms have been recovered from human

vomit Vomiting (also known as emesis, puking and throwing up) is the forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose. Vomiting can be the result of ailments like food poisoning, gastroenteritis, pregna ...

feces Feces (also known as faeces American and British English spelling differences#ae and oe, or fæces; : faex) 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 ...

,Yamada, M., et al. (2012)
Two human cases infected by the horsehair worm, ''Parachordodes'' sp.(Nematomorpha: Chordodidae), in Japan.
''The Korean Journal of Parasitology'' 50(3), 263-67. and

urine Urine is a liquid by-product of metabolism in humans and many other animals. In placental mammals, urine flows from the Kidney (vertebrates), kidneys through the ureters to the urinary bladder and exits the urethra through the penile meatus (mal ...

. When worms are expelled from the gastrointestinal tract, their mode of entry was likely ingestion of contaminated food or water, or of an infested insect. When present in the urine, the worm may have entered the

urethra The urethra (: urethras or urethrae) is the tube that connects the urinary bladder to the urinary meatus, through which Placentalia, placental mammals Urination, urinate and Ejaculation, ejaculate. The external urethral sphincter is a striated ...

from the

anus In mammals, invertebrates and most fish, the anus (: anuses or ani; from Latin, 'ring' or 'circle') is the external body orifice at the ''exit'' end of the digestive tract (bowel), i.e. the opposite end from the mouth. Its function is to facil ...

or while the victim was swimming in contaminated water. Horsehair worms are not considered

pathogen In biology, a pathogen (, "suffering", "passion" and , "producer of"), in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a Germ theory of d ...

ic or

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The ent ...

on humans and their presence in the body is incidental. Adult worms, as in some other Nematomorpha genera, may squirm in a tangled ball resembling a

Gordian Knot The cutting of the Gordian Knot is an Ancient Greek legend associated with Alexander the Great in Gordium in Phrygia, regarding a complex knot that tied an oxcart. Reputedly, whoever could untie it would be destined to rule all of Asia. In 33 ...

; horsehair worms are also referred to as gordian worms.

Diversity

As of 2010 there are 79 species in the genus. Gordius fulgur 001

References

{{Taxonbar, from=Q4039607 Nematomorpha