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Life in Freshwater

Horsehair Worm (Gordius sp.)

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Horsehair Worm

Also known as Hair or Gordian Worms, they belong to a little known phylum group, the Nematomorpha. The name is similar to the Nematode worms but they have little in common. The Horsehair Worms are very distinctive in the adult form, resembling a thicken piece of hair. The body can be very long but generally around 200 mm. However, it is only about 0.5 mm in width. It is not segmented and the dark brown body is very "stiff" or wiry, not bending easily. It has a thick cuticle covering. The tips of the body are very blunt; the posterior is forked or lobed. In the male there is a distinct curvature within the cleft of the fork. They may be found curled up around vegetation or extended when swimming.

The adult is the stage most likely to be encountered and this will be in sluggish rivers and ponds where the vegetation is thick. Where they are found the Horsehair Worms may be abundant. A number of different species are found in Europe and the group is well represented across the continent.

ECOLOGY: Horsehair Worms are little understood. They appear during late spring and summer in ponds and weedy rivers; coiled up on the vegetation or swimming with a waving, undulating movement. These are the adults and are believed not to feed as they have no gut present. After mating the female lays strings of eggs encased in sticky jelly on to the aquatic vegetation. Upon hatching the parasitic stage commences and the knowledge about them becomes limited. The larva enters an insect. The species are not especially specific and they may pass through several hosts. For example, the worm larvae may enter the body of a dragonfly larva where they feed within the body fluids. Once feeding is complete they may enter another insect or it could be that the host is consumed by the second host. Either way they may ultimately appear within terrestrial insects such as beetles, crickets and grasshoppers. When development is complete they fill the hosts body cavity. They then bore out of the body and re-enter water again as an adult to lay eggs and die.

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