Definition of "black rat"

The black rat spread wherever they settled, and so tied was it to Roman habitats that it became extinct in Britain following the Roman withdrawal, only to reappear in Norman times. Thereafter the black rat prospered - until the arrival of the larger brown rat (also known as the sewer rat or Norway rat), which reached Britain at about the time of the Hanoverian succession in the eighteenth century.

2018, Tim Flannery, Europe: A Natural History, page 272