The first description of a Mermithidae–Linyphiidae parasite–host association is presented. The nematode is preserved exiting the abdomen of the host, which is a juvenile Tenuiphantes species (Araneae, Linyphiidae), collected from the Isle of Mull, UK. An updated taxonomic list of known mermithid spider hosts is provided. The ecology of known spider hosts with regard to the direct and indirect life cycles of mermithid worms suggests that both occur in spiders.