Hi Stephen,

That is an very interesting find!

It is a nematode--most likely one from the family Mermithidae. Mermithid nematodes have free-living adults that can be found in soil or in water, and the one you found is an adult. The juvenile stages are internal parasites of a variety of invertebrates including insects, spiders, scorpions, crustaceans, earthworms, leeches and molluscs. They do not parasitize vertebrates (e.g. people, pets or livestock), though, so no need to be concerned about that.

Adult mermithid nematodes are sometimes seen in spring or early summer during damp weather when they come out to mate or lay eggs.

Hope that helps!