bstract. In the Silurian (Wenlock to Pridoli) of Saaremaa (East Baltic), large and deep Osprioneides borings have only been discovered in the lower Sheinwoodian stromatoporoids. Osprioneides borings played minor role in the general bioerosion (5.2 % of bioeroded stromatoporoids) in the Sheinwoodian of Saaremaa, but they were not too rare occurring in 4.7 % of all stromatoporoid specimens in a muddy open shelf facies.