Paragordius varius may communicate via chemosensory receptors located throughout their bodies that may be used in the free-swimming larval stage to locate their intermediate hosts. These receptors also have the ability to sense the presence of water when their definitive host is near their preferred aquatic environment. This ability helps the fully developed adult P. varius to know when to begin a series of manipulations on the host to get it to enter the water. Finally, these chemoreceptors may aid P. varius in locating a mate during its free-living adult form.
Communication Channels: chemical
Other Communication Modes: pheromones
Perception Channels: chemical
Paragordius varius is not considered a threatened or endangered species and therefore is not protected under conservation laws.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
Paragordius varius typically completes larval development within the egg 10-12 days after being laid. The fully developed larva will remain in the egg for another 7-10 days before hatching. Larvae are free-swimming and must find an intermediate host to infect within a few days or they will not survive. This intermediate host is most commonly an aquatic insect that is also in its larval stage. Infection occurs when the P. varius larvae bore into the tissue of the host using the hooks located on the anterior portions of the body. Immediately following infection a larva will form a cyst, typically in the intestine or musculature region of the host and remain in this dormant stage throughout the winter. The cyst is unaffected by and has no effect on the various phases of metamorphosis the aquatic insect undergoes during the winter and early spring (Hanelt & Janovy, 2004). Once the intermediate host has completed metamorphosis it flies to land where it may encounter the definitive host (an orthopteran) of P. varius. Transition to the definitve host is necessary for a larvae to develop into an adult. Infection of the definitive host can occur via direct predation of the insect by the host or, more commonly, when the insect dies (from causes not related to the larva) and its carcus is consumed by the definitive host. Once inside, a larva moves to the body cavity of the definitive host where it will complete development. A larva grows from approximately 10 mm to over 120 mm in length and from 93 µm to 400 µm in diameter in under 30 days. The adult cuticle develops around 20 days after infection of the definitive host. The larva has a physiologically active epidermis and intestine at the start of development, but activity tapers off as the intestines begin to decrease in size and the larval epidermis is replaced by the adult cuticle (Schmidt-Rhaesa, 2005). This represents a shift in the organism from a parastic larvae to a non-feeding adult form. Total development is short, only taking around 30 days, which allows for P. varius to produce up to three generations within a single year (Thorpe & Covich, 1991). Once it has reached adulthood P. varius will emerge from the definitive host when the host is near its preferred water habitat, usually during the late spring or summer. Paragordius varius may be able to manipulate its host to encourage it to enter the shallows of a body of water, the preferred habitat for adult P. varius. This theory is still being investigated (Hanelt et al., 2005).
Development - Life Cycle: metamorphosis ; diapause
At this time, P. varius is not known to have any steady, significant economic impact other than the medical costs that ensue on the rare occasion when a human is infected with the worm.
Paragordius varius has no detrimental effect on its intermediate hosts (typically aquatic insect larvae) and does not significantly affect the population density of its definitive orthopteran hosts.
The only significant role that P. varius may have in an ecosystem is possibly altering the behavior of its definitive orthopteran host. Infection with the P. varius larvae may cause erratic behavior in the definitive host, bringing the host close to a body of water. The larvae sense the presence of their preferred aquatic environment and manipulate their host to enter the water, where the parasites emerge as adults.
Ecosystem Impact: parasite
Species Used as Host:
Adult P. varius worms are non-feeding. The larvae are parasites of their definitive host and can absorb nutrients from their hosts through the cuticle and into their gut (which becomes severely reduced and non-functioning in adults). This absorption of nutrients can result in some weakness in their definitive hosts but is typically not fatal.
Animal Foods: body fluids
The distribution of Paragordius varius is throughout both North and South America. This horsehair worm has been reported from the northern-most portions of Canada throughout the United States most commonly along the Eastern coastline and near the Great Lakes Region. Twenty-six states (including Hawaii) have had confirmed sitings of P. varius. This species has also been observed in Cuba, in Central America ranging from Costa Rica through Guatemala, as well as in the South American countries of Brazil, Argentina, and Columbia.
Biogeographic Regions: nearctic (Native ); neotropical (Native )
Paragordius varius adults live in quiet freshwater habitats such as lakes and slow-moving streams. In some cases adults may even be found in puddles or other places where rainwater commonly collects. Adults are non-feeding and are most commonly found near the shoreline to facilitate mating. Females may go on land briefly to lay their eggs before returning to the water, but this is not necessary and it is not uncommon for an adult to never leave the shallows of their freshwater habitat.
Eggs can survive on land or water. If they are deposited on land it is usually near the shoreline and the string of eggs is wound around a blade of grass. Eggs laid in the water are deposited close to the shore and may or may not be anchored to some type of aquatic vegetation.
Larvae must develop within the body cavity of a member of their definitive hosts, the Orthoptera.
Habitat Regions: temperate ; tropical ; terrestrial ; freshwater
Terrestrial Biomes: savanna or grassland ; forest ; rainforest
Aquatic Biomes: lakes and ponds; rivers and streams; temporary pools
Wetlands: marsh ; swamp
Other Habitat Features: riparian
Paragordius varius survives for around one year. The majority of that time is spent in a dormant cyst stage within the intermediate host. Adult P. varius survive only a matter of one or two weeks after exiting their definitive hosts if they do not copulate. If copulation does occur, males will die almost immediately thereafter and females will die one to two days after she finishes depositing her eggs.
Average lifespan
Status: wild: 1 years.
Paragordius varius is a horsehair worm with a slightly off-center mouth and distinct grooves running along the body both dorsally and ventrally. The worm has a cylindrical body shape, with a slight decrease in diameter towards the anterior and posterior portions of the body. This decrease is exaggerated more in the females than the males. In both males and females, the body is typically light brown with a darker brown ring surrounding the anterior-most portion of the body. The body itself is enclosed in a cuticle that is densely covered with closely-spaced rounded areoles which are covered with small bristles. The area between the areoles is charcterized by the presence of cuticular rims, giving the illusion that the cuticle is covered in stripes. The areoles themselves vary between 20-30 µm in size and the majority of them contain a rounded nodule known as a tubercle at their center. These tubercles project an average of 6 µm above the cuticle of the worm.
Adult males reach an average of 170 mm in length but generally range from 120-290 mm. The posterior end of the body is bifurcating, meaning that it is divided into two elongated lobes averaging between 560-700 µm in length and between 140-150 µm in diameter. The cloaca is oval-shaped and is found between 170-210 µm from the point of bifucation of the lobes at the posterior end of the worm. Cone-shaped bristles approximately 8 µm in length are found on either side of the cloaca and form several lines at the ventral anterior end of the worm. At the posterior-most end of the worm the bristles are found on the inner ventral portions of the bifurcating lobes but do not occur at their tips.
Adult females are slightly larger than males ranging from 120-310 mm in length but have a similar diameter. The posterior end of the adult females differs from the male in that it is divided into three lobes instead of two (trifurcating versus bifurcating). The lobes do not have either bristles or tubercles on their surfaces and are slightly larger than in males, varying in length from 790 to 820 µm and in width from 190 to 230 µm. The cloaca has a similar positioning to that found in males but is more rounded in nature. Paragordius varius larvae are pure white during the entirety of the developmental period. Pigmentation takes place only slightly before the adult emerges from its host and the color is never altered. A larva has two primary body regions separated by a septum. The anterior portion of the body has hooks and stylets (which are lost in the adult form) and the posterior portion includes a gland and another morphological form that may be the beginnings of the intestine.
Range length: 100 to 470 mm.
Other Physical Features: bilateral symmetry ; polymorphic
Sexual Dimorphism: female larger; sexes shaped differently
No predators for P. varius are known. However, adult worms have been known to be accidentally ingested by numerous species such as dogs, cats, and even humans.
Adults typically mate one to two days after they have left their definitive hosts. They will spend their time swimming in the shallows and may or may not move up onto land near the edge of the water to mate. When a male and female initially encounter each other, the female will give a stimulus that signals the male that she is ready and willing to mate. During copulation there is no penetration and the male simply releases his sperm almost immediately after the female gives the stimulus. The male has little to no control over the direction of his sperm and many times the sperm does not land on the appropriate posterior area of the female and conception does not occur. If the sperm does manage to land on the females' posterior end, it forms a large circular glob. The glob gradually passes into the seminal receptacle of the female, normally within 24 hours after mating.
Mating System: monogamous
Eggs are typically deposited in strings varying from 0.2-0.4 mm in diameter. Up to 6 million eggs may be layed at once and a female may continue to deposit eggs continuously for a 24 hour period. If the female has mated on land she will most likely wind her string of eggs around a string of grass or anchor it to some other structure. Other females will lay their eggs freely in the aquatic environment. Males die almost immediately following copulation and females die one to two days after depositing eggs.
Breeding interval: Paragordius varius breeds once in its lifetime.
Breeding season: Breeding season is usually late spring, early summer.
Key Reproductive Features: semelparous ; gonochoric/gonochoristic/dioecious (sexes separate); fertilization (Internal ); oviparous
Paragordius varius does not partake in any paternal behaviors. Adults are typically deceased before their offspring hatch.
Parental Investment: no parental involvement
Paragordius varius is a parasite species in the horsehair worm group (Nematomorpha). They cycle between terrestrial and aquatic habitats and are most commonly known for their ability to manipulate their definitive host to jump into a pool of water, which allows them to complete their life cycle.[2] Adults are over 10 cm long and 400 μm in diameter.[3] P. varius is usually found in water or wet areas. The definitive hosts are mainly terrestrial arthropods, most often carabid beetles, crickets and praying mantids.[3]
Paragordius varius have a slightly off-center mouth and distinct grooves running along its cylindrical body. Male worms can grow to be 12–29 cm in length whereas females are generally longer and can grow to be 12–31 cm in length. This parasite is a pseudocoelomate whose body consists of an areole containing cuticle layer, monolayer hypoderm, muscular layer, ventral nerve cord and a digestive tract.[4]
The life cycle of P. varius includes a terrestrial and an aquatic stage. Adults worms emerge from their insect hosts late spring or summer. They swim in the shallow waters in search for a mate.[2] Upon encounter, the female signals to the male that she is ready and willing to mate.[5] No penetration occurs during copulation and the male releases his sperm immediately. However, if the sperm does not land on the appropriate posterior area of the female, conception will fail.[5] Once the sperm lands, a large circular glob forms which passes into the seminal receptacle of the female within twenty four hours of mating. Upon conception, the female P. varius lays a long, white, string of eggs and dies.[2] Up to as six million eggs are produced by a single female. Eggs are released into the water where they hatch into larvae. The larvae infect larvae of aquatic insects and snails that serve as paratenic hosts.[3] In these they encyst after 5–14 days.[2] As cysts they can survive the host's metamorphosis and wait for the host to be consumed by a definitive host.[6] In the definitive host, development takes approximately 30 days. After 25 days of infection differences between males and females can be seen. Around the same time the gonads probably start to differentiate between the sexes.[3]
The life cycle of nematomorphs has 4 stages: First is the egg, which takes about 10–12 days to complete its larval development after being laid. Second is the pre-parasitic larva that hatches from the egg; the fully developed larva remains in the egg 7–10 days before hatching. Third is the parasitic larva that develops within an invertebrate host; larvae swim about freely in the water after hatching, and are ingested with water when insects drink. If the larvae does not find a host within a few days, they will die.[2] The larvae uses hooks on the anterior portions of the body to infect its host. Once inside a host insect, the larva penetrate the insect's gut and enter its body cavity and forms a cyst in the muscular or intestine region.[2] They mature and escape from the host in two to three months. When the intermediate host completes metamorphosis it comes across a definitive host and evolves into an adult. The final stage of the nematomorphs is the free-living aquatic adult; the development only takes about thirty days where the P. varius is able to produce three generations in one year. They break through the body wall of the host and become free-living. Eventually the P. varius will leave the definitive host when the host is near water. This is done by manipulating its host to migrate to a shallow body of water.[2]
This parasite is known to infect insect species in the order orthoptera. Amongst the host species are grasshoppers, crickets, cockroaches, snails, mosquito larvae, or other small aquatic animals and insects. Mammals are not capable of being infected. However, dogs, cats, and even humans have been known to swallow adult worms accidentally.[7]
Like many horsehair worms, P. varius can alter its host's behaviour.[6] It does this at least in two distinct ways.
In the definitive cricket (Acheta domesticus) host P. varius can reduce the time spent calling of males. Male crickets call to attract females, but are likely to also attract predators. To reduce the risk of predation P. varius reduces the calling rate of its host.[6]
Second, to complete its life cycle, P. varius can manipulate the behaviour of its definitive host to make the host more likely to enter a body of water.[2][6]
Paragordius varius has been found all across North and South America ranging as far north as Canada and as far south as Argentina.[2] It prefers environments containing bodies of water needed for reproduction. P. varius has also been found to be able to withstand temperatures as cold as -70 °C. It can be frozen at this temperature for weeks and when it thaws out, it is still completely capable of infecting its next host.[8]
This species prefers lakes over streams.[9]
{{cite journal}}: Cite journal requires |journal= (help) Paragordius varius is a parasite species in the horsehair worm group (Nematomorpha). They cycle between terrestrial and aquatic habitats and are most commonly known for their ability to manipulate their definitive host to jump into a pool of water, which allows them to complete their life cycle. Adults are over 10 cm long and 400 μm in diameter. P. varius is usually found in water or wet areas. The definitive hosts are mainly terrestrial arthropods, most often carabid beetles, crickets and praying mantids.
