Like it or not, rats are here to stay

IN MY part of the country the grain harvest has been under way for several weeks now.

The country roads are full of slow convoys of traffic backed up behind combine harvesters or huge green trailers full of malting barley. And along the road verges and in the fields of new stubble you suddenly start seeing rats.

Rats are normally quite nocturnal animals but the bounty of spilled grain tempts them out in the daylight hours. Much of the grain they collect will be stored under ground for use during hard times in the winter.

People tend to have quite strong reactions to rats. There were two women visiting my house the other day when the topic came up in conversation.

The first woman was a rat lover. She had kept white ones as pets and enjoyed watching the behaviour of brown ones in the wild. The other women had such a strong phobia about them that she had to leave the room until the conversation turned to other topics.

My own view of them is somewhere between these two extremes. I can accept that they’re a rather fascinating part of our wild fauna and that they are intelligent and adaptable animals with an interesting social life. On the other hand I don’t like having them around the place and, like most poultry-keepers, I sometimes have to control their numbers with poison, traps or a shotgun.

The animal we are talking about is, of course, the brown rat, Rattus norvegicus. The smaller black or ship rat is Ireland’s most endangered mammal, and may even be extinct in this country.

Nobody seems to care very much about its status because, after all, it’s a rat and therefore not a popular or fashionable species among conservationists.

BROWN RATS have been in Ireland for less than 300 years. Some authorities give an introduction date of 1722. Certainly there are records that show that they had become a serious pest in Dublin by 1730.

The species originated in the Far East, probably China, and was inadvertently spread by humans along overland trade routes and in sailing ships. The Latin species name norvegicus probably originated from the fact that the first specimens in this part of the world arrived on a sailing ship from Norway and it was wrongly assumed that the species originated there. The Irish name francach donn is based on another wrong assumption — that brown rats originated in France.

Today, they are an extremely widespread species in both urban and rural Ireland.

They play an important ecological role as a food source for predators. They are the main prey of the barn owl, an endangered species in this country, and are also eaten by foxes, stoats, dogs and cats.

But an adult brown rat is a dangerous quarry and most predators concentrate on young or adolescent rats. The infant mortality rate among brown rats is over 90%, which is probably just as well. Adults don’t live very long either, though they have reached three or four years old in captivity.

What most people want to know about rats is how best to control their numbers. Unfortunately there isn’t a best way. Rats are neophobic, which means they are very wary of any new object in their environment, like a trap, and of any new taste, like a poison. They are also very good at developing resistance to poisons. As Hayden and Harrington note in their authoritative book Exploring Irish Mammals, “It seems that the evolutionary battle between the chemist and the rat will continue into the foreseeable future.”

And we should probably be on the side of the chemists. Rats can spread an amazing list of diseases, several of them fatal.

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