April 9th, 2012

Ann Vole

Where did Norway rats come from?

Where did Norway rats come from? Norway rats and roof rats are two species found associated with humans and as such have moved around the globe so it is less obvious where they were located originally. One genetic study of most of the members of the Rattus genus found the following species to be closest to R. rattus and R. norvegicus genetically: R. satarae and R. exulans. These two species are found near oceans in India and the Indonesia-South China respectively. I believe the origin of the story that Norway rats came from Mongolia is connected to looking for the Black Plague bacteria natural reservoirs in the wild and they have one in the marmots in Mongolia. A different study speculated that Genghis Khan and his crew of Mongolian warriors traveled quickly from China to Russia via Mongolia and shortly after, plague outbreaks happened along that route. I also learned separately that Mongolians often took live animals for meat including the plague-carrying marmots. The reservoir for plague in Russia is probably the suslik (ground squirrels) who have closely related fleas (that spread the bacteria). If this is the case, rats may not be involved with the spread until later when the plague reached the port cities where the two species of rats (Norway and roof) move around Europe via shipping. So, where did the rats originate? It is strongly suggested to be somewhere between India and Indonesia AKA Burma and Bangladesh. Swampy jungle (found on much of the coastal area in these two countries) would work nicely as a home for the two species who seem to co-exist where roof rats live in trees and Norway rats like the wet areas below.