RECENTLY I have heard from many friends and acquaintances about plagues of rats and mice. It seems that uncared for gardens, particularly unkempt compost heaps, spare parcels of land and disused or empty buildings are providing perfect breeding conditions for rats, mice and other rodents.

Just how many rats and mice there are isn’t ever easy to quantify. Counting populations of any of our native mammals isn’t easy except in one exceptional case.

We do have fairly accurate figures for one of Britain’s most numerous mammals and certainly the most destructive: there are just under 70 million human beings living here — and that includes you and me.  
 
There are only just a few wild mammals that outnumber we humans and a dozen or so mammals get near that 70m human population figure.

Top of the list is probably the common or brown rat (Rattus norvegicus). Worldwide the common rat is considered the second most successful mammal after humans. About 82 million live in Britain.

Then comes the house mouse (Mus musculus) with an estimated 76 million. Field voles (Microtus agrestis) almost equal house mice at 75 million.

The common shrew (Sorex araneus) comes in at number four with an estimated population of 43 million. At number five is the wood mouse (Apodemus sylvaticus) at 41.6 million.

Both wood mice, field voles and common shrews are sometimes mistakenly identified as “field mice” particularly when they venture into your house or garden.

Strangely many internet sources will tell you the commonest wild mammal in Britain is the rabbit. Perhaps they find rats and mice and their rodent relatives too distasteful to include in their cuddly data.

Introduced by the Roman legions as mobile fresh meat, rabbits now number at least 40 million animals, but annual populations fluctuate wildly.

Let’s get back to the rats. There are actually two species of rat in Britain. Both share perhaps the worst reputation for being dirty and disease ridden.

Least common of the two is the very rare black rat (Rattus rattus), also known as the ship rat, or sometimes confusingly as the house rat.

The black rat is black to light brown in colour with a lighter underside. It eats anything.

It originated in India — where some religions treat it as a sacred animal — and south-east Asia, then spread to the Near East and Egypt and throughout the Roman empire, reaching Great Britain as early as the 1st century AD.

In domestic settings the black rat is prey to cats and owls, in country settings to weasels and foxes — but black rats are agile and fast climbers. In addition to agility, the black rat also uses its keen sense of hearing to detect danger and quickly evade predators.

Today the black rat is almost extinct in Britain. The last permanent population was on an island in the Hebrides, but this was eradicated in 2018. A few have been spotted in Southwark in London and Avonmouth and some small populations live on the Channel Islands of Alderney and Sark.

The brown rat is far more numerous all over Britain. Originating from central Asia, the brown rat reached us in the 1700s.

The brown rat has grey-brown fur, a pointed nose, large, bare ears and a long, scaly tail. This is an incredibly adaptable mammal and can be found almost everywhere in Britain where it can find shelter and food. Typically it is about 15-30cm and may weigh 200-300g, living for up to three years.

Brown rats eat pretty much anything, from fruit and seeds to human food waste, insects, birds’ eggs and even small mammals. They cause much damage by gnawing electrical insulation and plastic plumbing.  

Brown rats are particularly common around towns and cities where they live in loose colonies and dig their own burrows. They have really benefited from the lack of maintenance of gardens and buildings during the pandemic.

Compost heaps and other piles of vegetable rubbish and twigs and branches seem to make the most attractive homes for large colonies.

A female brown rat can breed from around three months old and has an average of five litters a year, each of up to a dozen young.

There are only two animals that can be confused with the brown rat. One is the amazingly rare black rat. The other is the very similar looking and much threatened water vole (Arvicola amphibious). This has a much rounder face, small ears that do not protrude and a furry tail — but many a canalside water vole has been despatched as a rat.

Over the years, as I studied various wild animals, I began to become aware of a widely held belief about brown rats. It was commonly said that wherever you were in Britain, particularly in towns and cities, you were never more than six feet away from a rat.

The old adage almost certainly originated in former Ministry of Agriculture propaganda. It was one of the many public health announcements issued to promote hygiene in homes. I doubt that it was ever really true.

But rats did live and were often seen or heard in roof spaces, under floorboards or in sewers. They were even more ubiquitous on farms and agricultural premises. Rat hunts at harvest were always good fun as well as controlling rat populations killing hundreds of rats at a time.

Today rats or mice in your home still carry many risks. They can spread disease and both rats and mice can cause a great deal of damage to the structure of your home as well as eating and contaminating your food.

Rats and mice can even cause serious structural damage to homes, indeed to virtually any type of building through gnawing, nest-building and smelly piss and poo.

Rats and mice will chew on just about anything that they see as useful in building their nests. This could be wood, paper, cloth or books.

Insulation is not safe from them either. They will tunnel into insulation inside walls and attics, either to make a home their or to gather soft materials for their nests. They also will gnaw on the insulation around electrical wires. This has often caused serious fires.

Rats have no respect for any item in attics, cellars or garages — they will chew irreplaceable family heirlooms, valuable paintings and important documents.

The more hidden away and undisturbed an item or area is, the more likely a rat or mouse is to see it as a comfortable, secure home. When the animal travels around your home seeking food, water and nest material it will leave behind poo pellets and urine trails. These contaminate surfaces and foods and can spread diseases as well as leaving a scent trail for other pests.

Food items in cardboard boxes or paper wrapping provide a double bonus. The packaging can be used for nesting after they eat the food inside.

All kinds of traps and poisons are available to kill both rats and mice but be very careful if there are young children or inquisitive pets about — always follow the instructions.

Before the widespread Tory public service cuts, most local authorities had a dedicated pest control department — some still do. If not you will need to find a privatised company — there are over 700, if you need professional help.

Of course, pet cats are a great way to discourage rats and mice. There are well over 10 million pet cats in Britain and an extra two million cats that have gone feral and are living wild, mostly on a healthy diet of small rodents. One drawback is that many pet cats have the mistaken belief that their owners love a bloody rodent corpse delivered as a gift as often as possible!