Keep eye out for the super-size-me rat

IF THE Keep Britain Tidy campaigners are to be believed, there has been a 20% rise in the number of rats on our sister island.

Not only have rat numbers increased, a new breed of super-rat has emerged. He is bigger, tougher and lives longer than his ordinary cousin. The growth of fast food outlets and the careless ways of its citizens are to blame for the new terror stalking the land, the campaigners say. Waste food, in the form of half-eaten burgers crusts and crisps, discarded on the streets, is providing a bonanza for rats. There has been a 450% increase in the amount of waste food littering Britain’s cities since 2001.

To highlight the problem, a stunt lady entered a large Perspex box in London’s Golden Square recently. The container was full of hungry rats, surrounded by waste food. Unfortunately, the organisers failed to alert the Irish Examiner in advance of the spectacle so I was not there to observe it. But has one stunt inspired another? Is the super-rat story itself a publicity stunt, invented to make the feckless patrons of fast-food joints more socially responsible? Is there really a new form of rat around? Are rodents actually getting bigger?

The campaigners say that there are about 60 million rats in Britain, one for every person. This estimate is probably on the low side but undertaking a census of animals is notoriously difficult and especially so for rats, which live underground and seldom appear in daylight.

Nor are rat populations stable. Rodents live in a world of multiple births and sudden deaths. A female becomes sexually mature when only eight to 12 weeks old. She could produce up to five litters in a year, with seven to nine babies in each. Rats have to be prolific breeders if they are to make good their numbers following disasters. A sudden downpour, for example, may flood underground pipes and drains, trapping and drowning thousands of rats. Death is ever present and over 90% of rats never reach their first birthday.

Although they may be difficult to census, you don’t need rocket science to know that if you provide food for rats, their numbers will increase. If the streets of Britain are littered with food waste, rats will benefit. Well-fed laboratory rats live longer than ones on a more limited diet, so rats which patronise fast food outlets probably improve their survival prospects.

That rats are getting bigger is more of a puzzle. Size is a mixed blessing if you’re a rat. You need to be lean and mean to negotiate narrow burrows and enter small holes. However, according to the Keep Britain Tidy website, the super-rats can still “squeeze through a gap just over 1cm wide, making it easy for them to get into our homes”. This seems an extraordinary claim. Whatever the squeeze limit, becoming bigger would seem to limit a rat’s options.

Brown rats seldom enter homes in any case. This was the prerogative of the black rat, now no longer with us. It was smaller and slimmer, living much closer to people, which is why its fleas carried the plague to humans.

The increase in the size of rats, the campaigners say, can be blamed on the change in diet. The brown rat is traditionally a rural dweller, eating cereals high in carbohydrates. Junk food, however, is protein-rich and eating this, the anti-rat lobby claims, has resulted in the larger rat.

There are precedents for such a development. The rats of the trenches during the First World War were said to have been “as big as cats”. Allowing for exaggeration on the part of war-veterans, some of the animals may well have been bigger than their more normal cousins. In the hell of the trenches, death and decay abounded. Corpses lay rotting in no man’s land. Discarded food and organic waste were everywhere. The trenches were a rat paradise.

Other creatures, too, changed size during the war. After the naval Battle of Jutland, local fishermen reported record catches of exceptionally large eels. The dead bodies of sailors were eaten by eels.

However, size changes in wild creatures are not always related to diet. When birds are caught for ringing, their weight is recorded and the British Trust for Ornithology has a vast archive of weight information. Ornithologist Andy Gosler, examining the data, noticed that great tits became heavier during the 1960s. Pesticide pollution turned out to be the culprit. Organo-chlorine chemicals, such as DDT, poisoned the sparrowhawks which hunt small birds. Tits need to be slim and agile if they are to escape from an attacking hawk. When the hawk population crashed, it was safe for great tits to put on weight. When the pesticides were banned, the birds of prey returned and the great tits became lighter.

The principal danger from rats is contamination of food destined for human consumption. Rats are vectors for several nasty diseases but they have a role to play in our cities and towns. In the front line of the waste disposal brigade, these and other scavengers break down food waste, handing iton to the fungi bacteria and creepy-crawlies complete the recycling process.

Given our binge-drinking culture, Irish cities and towns must be just as attractive to rats as British ones, so perhaps the stunt lady should put on a performance here.

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