The presence of these rodents inside and outside the sewers is not a new problem in the French capital. The research advances by several decades the arrival in America of the gray rat, also called brown or Norwegian ( Rattus norvegicus ), and places it around the year 1740.
Until now it was believed that this voracious species had arrived on the continent in the 1770s, but analyzes carried out on archaeological remains have shown that its presence dates back earlier. The authors believe that the gray rats reduced the availability of food for the common rats, causing the collapse of its population.