Grisly nature

Folklore had these parasitoid worms forming from the dropped hairs of horses when they were frequently found in horse troughs.

The Gordian knot is an illustration of a problem without a solution. An ox-cart which delivered a peasant named Gordias into Phrygia who became its king, was tied up with a knot so intricate that is was not possible to undo it, but whoever did would rule the whole of Asia  Alexander the Great tried and failed so sliced it in half with a stroke of his sword hence the Gordian knot/

A phylum of parasitoid invertebrates comprising the marine Nectonema and freshwater Gordioida. There are 350 different known species throughout the world.

Adults can reach a length of between  50 and 100mm and in extreme cases 2m but only up to 1mm in diameter.

They have an external dark brown cuticle, which is almost all muscle which gives them a hard and wiry feel. This muscle arrangement results in them  twisting into intricate knots - hence the genus name Gordius resembling the classical Gordian Knot. 

Nematomorpha showing the eponymous knotting behaviou

They lack any excretory, respiratory or circulatory system.  The eyeless head may have a darker band below the paler tip.

The tail end of females is rounded but males of most genera genital papillae showing as a cleft tail.  Males of Gordius genus have a crescent-shaped fold above the two lobes.

Male nematomorpha with bifuricated anterior.

They exist in their external adult form purely to reproduce.

The life cycle is complex and almost wholly parasitic.

Long strings of gelatinous eggs are laid in freshwater.

From these develop planktonic larvae which have a boring apparatus with which to enter its first host, aquatic invertebrates typically diptera or trichoptera larvae.  Once inside this host, they encyst in the gut of the invertebrate.

In turn, these invertebrates are predated upon by freshwater or terrestrial invertebrates, typically Coleoptera or Orthoptera with Carabidae being a common host.

Once inside this host, the larvae develop into the adult worm-like form.  They grow to fill the internal cavity of the host but also influence it to seek out and enter water where the host drowns.  Once this is achieved, the adult Nematomorpha will abandon the host and seek a mate to reproduce in freshwater where the next season’s eggs are laid and the adults die.

 The National Biodiversity Network shows 251 records, the majority of which were recorded in Wales and a few in Scotland.  The South West has no records at present.  However over the last three years specimens have been increasingly recorded in Cornwall and on Lundy. 

Although reportedly adults emerge from their host in late summer or early autumn, on Lundy adults are typically found in shallow temporary puddles on the island road in November and December.  In Cornwall, they have been recorded during Riverfly surveys in small streams in April, August, September and November.

I always search shallow puddles of the picture that eludes me, that of an adult emerging from its host.

Blogs I follow

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