Gordius aquaticus Linnaeus, 1758, Europe.
OTHER COMMON NAMES None known.
Body ranges from light to dark brown. Body length ranges from 4.7-19.3 in (120-490 mm) with a maximum diameter of 0.02 in (0.6 mm). Male posterior is bifurcating, female posterior entire. Male has postcloacal crescent, which is a parabolic fold of the cuticle just past the cloaca on the posterior end. Areoles are completely lacking.
Found throughout Europe. In the south, they have been reported from southern France to Turkey. In the north, they have been reported from Belgium to Finland.
Adults are free-living in freshwater environments. This species is often collected from ponds and from slower streams and temporary waters such as wheel ruts or puddles filled with rainwater. Juveniles develop within coleopteran hosts such as ground beetles.
The behavior of this group has not been intensively studied.
FEEDING ECOLOGY AND DIET
Parasitic during larval stage, non-feeding as adult.
These worms reproduce once per year. Worms either over winter within coleopteran hosts or as free-living adults in sediments or leaf litter. Adult worms emerge from hosts during late summer or early fall, and begin mating. Egg production begins about a month after copulation, and can last as long as four weeks. Larvae hatch from eggs and enter aquatic insect larvae such as midges or mayflies. Within these insects, parasites form cysts able to survive insect metamorphosis to adult flies. Flying insects, carrying cysts, are eaten by beetle hosts, completing the life cycle. Development to adult worms in beetle hosts may take up to three months.
As with all gordiids, this species does not infect humans. However, the accidental expulsion of this worm from its insect host in domestic water supplies, toilets, pools, and livestock watering tanks has caused much unwarranted distress. ♦
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