The Lyme Grass (Longalatedes elymi) is a species of moth of the Noctuidae family. It is found along the coasts of southern Sweden, southern Finland, Denmark, Estonia, northern Poland, northern Germany and eastern Great Britain. The wingspan is about 36 mm. Adults are on wing from June to August. The larvae feed on Elymus arenarius. They feed inside the stem of their host plant, usually below the surface of the sand.