Grass silage is a key source of forage for over-wintering livestock in Ireland. In the early 1990s Schizophyllum commune emerged as a contaminant of big-bale silage. A fungus rarely observed in Irish woodlands, S. commune is now commonly found on baled silage throughout Ireland and is also recorded on silage in Britain. Characteristics of the fungus on bales are described and potential consequences of its occurrence on silage are discussed.