Rats are Scotland's most maligned rodent, but they are not as prolific as we think

It is one of the great urban myths that you're never more than a few feet away from a rat, which if true would result in our stumbling across rats all the time.

But while their abundance may be an exaggeration, the rat is one of our most successful animals, being highly adaptable and equally at home in country or town.

They are typically found in areas where human activity provides food and shelter. Classic habitat includes farms, refuse tips, urban waterways and warehouses.

Although common, rat populations occur at much lower densities today than in the early 1900s when it was estimated that numbers in the UK matched those of humans.

Much of this reduction can be put down to improved hygiene practices and greatly enhanced pest control techniques.

More recently, the advent of the enclosed 'wheelie' bin has helped keep household rubbish more secure from foraging rats, although there are new fears that the longer periods between bin collections may result in a resurgence in numbers.

The undesirable aspects of the rat, however, should not detract from its fascinating social behaviour.

They often live in colonies, large or small, that can consist of smaller social units or 'clans' within the larger whole.

They are prolific breeders. A female can produce up to five litters a year, resulting in around 50 young, which themselves are able to breed only a few months later. But many predators take their toll on rat populations, including foxes, owls, buzzards and cats.

The brown rat should not be confused with its close cousin, the black or ship rat, blamed for spreading the devastating bubonic plague through Europe in the 14th century.

Ironically, the black rat today is extremely scarce in Britain and confined to only a handful of port and island locations, having been pushed out of former haunts by an inability to compete with the larger brown rat.

Closer scrutiny of the evidence surrounding the Black Death also casts doubt on whether the black rat was instrumental in spreading the disease. Both species of rat originate from Asia, with the brown rat being a relative newcomer to this country, coming in on ships in the early 1700s.

According to Robert Wilkie of Crieff-based Strathearn Pest Control, the three main problems caused by rats are disease, damage and contamination.

"They can cause serious damage by gnawing on various materials including electrical wiring and pipes resulting in floods and fires," he says.

"The main disease that rats carry is Weil's Disease, which is spread through humans coming into contact with rat urine. Contamination is another serious problem and many thousands of tonnes of cereal are wasted each year through coming into contact with rodents.

"Rats will happily live in your loft or basement and will come out when the house is quiet."

So, what signs should we look for if we're suspicious that there are rats about?

"People should look for holes in their gardens especially around compost bins as these are favourite places for them to nest," says Robert. "They may also see rat runs in soil or soft ground."

He adds that the brown rat is a great opportunist, making good use of any food that comes its way.

"Fairly recently we were called out to a local shop as the owners' biscuits had been going missing.

"It was a family-run business and the wife was convinced that her husband had been eating all the biscuits and had accused him a number of times, after which they decided something else was going on.

"After surveying their premises I found a stash of biscuits in the wall cavity which the rat had been stealing when the shop was closed. The husband was finally let off the hook."

This article was first published in The Scotsman, 16 April, 2011