They are common in wetlands , where they are responsible for marsh gas , and in the digestive tracts of animals such as ruminants and humans , where they are responsible for the methane content of belching in ruminants and flatulence in humans .
They are also common in the digestive tracts of many animals , such as ruminants and humans . They are responsible for the methane content of belching in ruminants and flatulence in humans .