Rove beetles (Coleoptera: Staphilinidae) are a group of diverse insects occurring in a range of different ecosystems, from the plains to the mountaintops. However, there are no reports in the literature of their presence in the tidal zone of the seashore. This is the first report of the presence of Paederus fuscipes Curtis on the coastal sands of the Caspian Sea, northern Iran. In all 14 counties of Mazandaran Province on the southern coast of the Caspian Sea, systematic monthly sampling of the beetles took place from May 2012 to April 2013. Samplings (30-min-person) were performed and specimens collected from the sandy seashore by gloved bare hands and identified using appropriate keys. To our surprise, all 1012 specimens collected were exclusively P. fuscipes Curtis, but with significant seasonal and geographical variations among the numbers of specimens collected. The distribution and activity of P. fuscipes were outstanding in Mahmoodabad and Fereidonkenar counties, with the highest abundance and frequency in September, posing a serious health threat to tourists and residents of these areas.