Pant y Sais Fen shares many similarities with the nearby Crymlyn Bog, the most extensive lowland fen in Wales. The reserve is home to the largest spider in Britain, the Fen Raft Spider (only 23mm long!), which is known from only two other sites in the UK. Regular breeding birds include Reed Warblers, Sedge Warblers, Cetti’s Warblers, Reed Buntings and Water Rail. While scarcer visitors include Marsh Harriers and Bearded Tits. The site is also home to an amazing variety of dragonflies and damselflies.