The Ship Rat (Rattus rattus)

The Ship Rat evolved in the tropical forests of Asia and likes a similar habitat here. It thrives in warm houses, hence its alternative name, the roof rat. It climbs well and eats fruit when it comes accross it, but it will consume almost anything.

Despite being cute and squirrel-like, with large eyes and ears, it earned a bad reputation as the vector of bubonic plague, which was transmitted via its fleas. It was slowly out-competed by the Common (or sewer) Rat, which arrived in Ireland in 1722. People associate the disappearance of plague with the arrival of this new rat species, which is less of a climber and does not occur, as often, indoors. This neat story, does not, sadly, fit with the facts. Bubonic plague arrived in Ireland in 1350 and the last outbreak was in 1650, so the Common Rat was some 70 years too late to get the credit for the end of plague. Ship Rats lasted a long time after that and thousands were still being killed in the ports of Dublin and Belfast in the 1930s. The last record of a Ship Rat on the Irish mainland was in the port of Cork in 1976.

The three C's – concrete (which, along with bricks, made buildings less rat-friendly), containerisation (along with steel hulls, it changed shipping) and the concentrated control (as they occur in buildings, they are easily targeted) have made the Ship Rat a rare animal. It is likely that the Ship Rat became scarcer faster in Ireland then in Britain due to the lack of timber-made houses when this country ran out of timber in the 17th century. It is now considered likely that the bacillus that causes plague itself burnt out due to a lack of susceptible hosts on the island of Ireland. However, bubonic plague is still found around the world, mainly in the big continental land masses of North America, Africa and Asia, where there are sufficient wild rodents to allow it to cycle, with occasional outbreaks in urban areas.

Another myth is that Ship Rats have ‘neophobia' – a fear of new objects. This fear is often displayed by the Common Rat and frequently frustrates efforts to control them by, for example, traps or baits, since both will be regarded as new objects and avoided. The consensus today is that neither Ship Rats nor House Mice show this behaviour. This is very probably another reason why the Ship Rat is no longer found on the Irish mainland and survives only on Lambay Island off the coast of Dublin.