||Our understanding of the ecological impacts of direct outdoor lighting has improved substantially over the last decade [1, 2, 3]. In contrast, the impacts of artificial skyglow — that is, artificial light that is scattered in the atmosphere and reflected back to the ground — have received comparatively little attention . Artificial skyglow extends the influence of direct lighting out to hundreds of kilometres from direct sources (for example street lights). It is the most geographically widespread form of light pollution, affecting 23% of the world’s land surface (between 75°N and 60°S) . Artificial skyglow illuminances are two orders of magnitude lower (0.2–0.5 lx) than light pollution from direct artificial light (typically 10–100 lx), but greater than moonlight (0.1–0.3 lx) and light from the Milky Way (0.001 lx). Numerous organisms from across the animal kingdom orient themselves during migrations using lunar compasses [6, 7, 8, 9], and are vulnerable to artificial skyglow across large (10–100 km) spatial scales. Here we demonstrate that artificial skyglow disrupts nightly migrations by the amphipod Talitrus saltator (commonly known as the sandhopper), which uses the sky position of the moon [9, 10] as a guide.