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Gordionus Chinensis

Gordionus Chinensis, a parasitic hairworm, belonging to the genus Diestrammena and phylum Nematomorpha, is found in the country of Japan.^[1]

Characteristics

Characteristics of these species include knob-like structures that occur in between cuticular areoles. During majority of their lives, they play the role of an endoparasite in a variety of insect species. Japanese Pray Mantids are commonly known as a host for these parasitic hairworms. Terrestrial insects are known to be the main host.^[1] G. Chinesis can grow as long as 10-20 cm in length.

Habitat

These hairworms are commonly found in fresh water habitats, but this only applies to one phase of their life cycle.^[1]

Life Cycle

An interesting characteristic of the host-parasite life cycle is that the hairworm transitions between two heterogenous habitats throughout its development. The first step of the hairworm life cycle is to find a mate in the aquatic habitat that surrounds them. Next, the female will lay her eggs in the water. The larvae will remain at the bottom of the water column where they can be eaten and encysted in aquatic animals. Hairworms can be passed from aquatic to terrestrial environments by hatching a ride through the metamorphosis process of the insect host (flying). The terrestrial host, such as grasshoppers and crickets, will then ingest the flying insect and the parasitic hairworm will grow as adults within 4-20 weeks. The hairworm will manipulate the definitive host (terrestrial insect) to jump into the aquatic environment during summer or autumn once the worm has reached the free living stage.^[2] When the definitive host reaches the water, the adult hairworm will emerge from within the host within several minutes and will once again begin to find a mate to begin a new life cycle.^[2] During the hairworm emergence, the definitive host will wiggle on the surface of the water causing a great deal of attention from its aquatic predators such as fish or frogs.^[2] Some parasitic hairworms may be ingested by aquatic non-host predators (accidental host).^[2]

Predation

The predation of trout on G. Chinensis is extremely common in the Japanese headwater stream of the Tostu River. Research suggests that hairworms were ingested by trout through their hosts. Parasites and their hosts are often consumed together even if the predator is not an actual host for that parasite. Specifically, a larger trout with a larger mouth is able to fully ingest the parasite and the host (ex. Cricket) that it resides in. This will prevent the hairworm from emerging into the digestive tract of the trout.^[3] Large trout are less abundant in the upper reaches of the headwater stream. This increases the hairworms survival rate due to them occupying the headwater stream where less, large trout are present.^[3] As previously mentioned, the mating and egg laying process of the male and female hairworm occurs at the bottom of the stream, or the lower reaches of the stream. With that, the hairworms are taking a huge risk since they may encounter a large trout predator in that area of the stream.^[3]