Black mould, also known as stachybotrys chartarum, is a toxic fungi that feeds on organic material like your insulation, sub-flooring, carpet, drywall, and upholstery. As it grows it releases spores, ingesting black mold spores on a regular basis can lead to dangerous health symptoms. It can aslo be green and have a musty smell to it. Black mould is caused by water leaks. If you have an external leak then a water leak investigation may be helpful if internal a plumbing leak may be the cause.