Professor ROB SMITH, Huddersfield University's Dean of Applied Sciences, views rats as the masters of survival. In the first of two articles he explains why ... and why you're never far from a rat!
RATS and mice like the same things as people and follow civilisations all over the world.
Of the two, it is rats that cause the most feelings of horror, or at least anxiety.
Concern about rats has increased recently because surveys by the pest control industry suggest rat problems are growing.
Many people think this is related to the amount of rubbish and, in particular, part-eaten food available to rats in modern towns.
In fact, it is hard to say if there are more rats than a few years ago and we do not really know how many rats there are in Britain.
In this article I will talk about why rats are so successful and why we have trouble in dealing with rat problems.
Rats and mice belong to a group of animals called rodents, mammals with very sharp front teeth that grow all the time. These teeth are very sharp and hard. Rats can bite through mild steel.
Rodents include squirrels, voles and several other families. The three rodents that have spread across the world are the common rat, found all over Britain, the house mouse and the black rat or roof rat, which used to be the native species in Britain but is now almost extinct here.
The common rat displaced the black rat from northern Europe in the 1700s and today the black rat is found mostly in warmer climates.
Both species are found in some countries and especially near sea ports where migration from ships helps to maintain the less common species.
Rats are social animals with high levels of parental care. They are highly intelligent and try to avoid being killed by other animals by choosing not to cross open spaces and moving along walls or banks, given the option.
Rats defend the territory of the social group rather than individual territories, and it is believed that a common rat can recognise up to about 10 individuals in its own colony and will chase strangers away.
Within the social hierarchy the largest rats get the food first and feed at preferred (safer) times.
Rats are mostly active at night but sometimes, if the commonest predators such as foxes are active at night, they will become active by day. Rats are very wary of anything new.
Rodents are unable to vomit and that could be a serious disadvantage because, if they eat something toxic, they cannot easily get rid of it, unlike people. Rats overcome this through having a very sensitive, highly developed sense of taste.
If a rat comes across a new food it will take in a small amount of it, taste it, swallow it and wait to see if it feels ill. If the new food has a bad effect, the rat will avoid that food for the rest of its life and also let other rats know about it.
This makes it difficult to control rats with fast-acting poisons. Their cautious behaviour prevents most of the population from being poisoned and fast breeding soon makes up the numbers.
Why should we control rats?
Well, rats and mice damage buildings, they can spread disease to both people and farm animals, they eat food meant for people and livestock and, perhaps most important for farmers, they contaminate food, reducing its value if droppings or urine are present.
A survey of rats on UK farms found that they carried 14 diseases that could be spread to other animals, including man.
Historically we associate rats with plague, carried from rat to humans by the flea.
Nowadays, one of the most serious diseases in Britain that is carried by rats is Weil's disease, which used to be associated with farm workers and coal miners, but is now more commonly found among water-sports enthusiasts.
For the farmer, the main problem caused by rats is contamination of grain or foodstuffs.
The best way to control rats is to prevent the damage - if there's no damage then there may be no need to kill the rats. Keeping rats away or out of the foodstore can be very cost-effective. Ways of doing this include general tidying up, keeping open spaces around buildings, and using well-fitting metal doors and containers that rats cannot bite through.
Predators such as cats have limited value and may help deter rats but, in general, are unlikely to control a large infestation.
Usually, rat poisons (rodenticides) are the fastest and most effective way of controlling rats.
* TOMORROW: The Yorkshire super rat.
* Wild rats have an average lifespan of about a year, with a wild rat population losing about 95% of its numbers each year.
* As in humans, female rats live longer than the males.
* Last year it was estimated that Londoners are never more than 20 yards (18m) from a rat.
* Litter and fly-tipping were blamed for the increased rodent population
* The number of rats in the UK has soared, posing a serious risk to public health, according to a study.