Juncus effusus
The larvae feed on the seeds of rushes ("Juncus" species), including "Juncus inflexus", compact rush ("Juncus conglomeratus"), soft rush ("Juncus effusus") and saltmarsh rush ("Juncus gerardii"), and supposedly also on woodrush ("Luzula" species). They create a trivalved, tubular silken case.