British Wildlife of the Week

Black Rat

Image Source: Kilessan

What is the rarest mammal in Britain? The pine marten, perhaps? The red squirrel? Water vole? Well, a 2018 study led by The Mammal Society, which determined that one in five British mammals face a high risk of extinction here, identified three species as the most endangered. One was the Scottish wildcat, which we’ve already covered on this blog; the rather vague estimate of between 30 and 430 pure, or almost pure, wildcats still live in the remote corners of the Scottish Highlands. Then there is the greater mouse-eared bat, the British population of which is thought to consist of just one lonely male living in a Sussex railway tunnel.

But the third and final mammal might surprise you. It’s a rat. The black rat, to be precise. It is now so rare in the British Isles that if it isn’t already extinct here, it almost certainly will be very soon.

Britain is home to two species of rat, the black and the brown, neither of which are native. The black rat – also known as the ship rat – was the first to arrive. Originating in tropical Asia, it may have landed on our shores as early as the 1st century with the Romans. The population was increased by thousands, perhaps millions, more rats over the subsequent centuries as countless ships docked around our coasts, allowing their stowaways to scurry ashore along gangplanks or down mooring lines. Agile, resourceful and intelligent, the rats spread from dockland areas to our cities and towns, scrambling up wooden beams, taking advantage of our waste, and nesting in roof spaces.

The black rat is smaller and slimmer than the brown rat, has a long, thinner tail, and has a greater predilection for climbing. Despite their name, however, their coats vary in colour from black to greyish-brown.

The black rat is a mammal of profound historical significance because of its close association with the bubonic plague. Thanks to recent studies, which have determined that the number of black rats living in rural parts of Europe was probably lower than previously thought, it is now believed that the rapid spread of the plague beyond ports and major cities was caused more by the lice, mites and fleas living on humans rather than by rats and their parasites. However, it still seems likely that fleas living on these rodents were responsible for initially bringing the plague to Europe via merchant ships, so they’re not completely off the hook.

The most famous of these plague pandemics – the Black Death – occurred between 1346 and 1353, and was the deadliest pandemic recorded in human history. It killed at least 3 million people in England – over half the population at the time – and reduced the world population from an estimated 475 million people to 350-375 million. Overall, it caused the greatest loss of human life in Europe prior to World War I.

A brown rat
The brown rat, contrary to popular belief, didn’t have anything to do with the bubonic plague. It is a much more recent colonist and didn’t arrive in the UK until a few hundred years after the plague first appeared.
Image Source: Pixabay

For a long time, it probably seemed inconceivable that anything could get rid of the black rat. But then, in the early 18th century, its cousin arrived: the brown rat.

One of the brown rat’s alternative names is the Norway rat because when it first started to appear in England in the 1720s, some people believed that it had come over on ships from Norway. In reality, these first immigrants probably arrived via trading ships from Russia, for the brown rat hadn’t actually colonised Norway yet – and wouldn’t do so for another 30 years. We now know that the brown rat originated in central Asia, but even today it bears the scientific name of Rattus norvegicus, which literally means ‘Norwegian rat.’

A brown rat in the grass
The brown rat was once called the Hanover rat by outspoken critics of the monarchy, who wished to link the many problems of 18th century England with the House of Hanover, the new ruling family at the time.
Image Source: Dunpharlain

In the 300 years since its arrival, the brown rat has almost completely displaced the earlier invader. Not only is the brown rat bigger, bolder and more aggressive than the black rat, it can also eat a wider variety of food and deal with greater weather extremes than its smaller, slimmer cousin, which prefers warmer climates. Any rat that you see wild in the UK today, therefore, will almost certainly be the brown rat, which now outnumbers the human population of the country. A few black rats occasionally turn up in major seaports or cities, foraging in disused buildings and warehouses, but these are likely to be new arrivals, having reached our shores on incoming cargo ships.

Unfairly or not, the black rat has, for a long time, been blamed for the cause of untold human loss and misery. And although today it has been partially exonerated for its role in the spread of the bubonic plague, old grudges die hard. Few people have clamoured to try and save or protect the black rat. They are, after all, non-native, extremely common elsewhere in the world, and generally viewed as pests and vermin, both to ourselves and our resident wildlife.

The last viable population of British black rats lived, until quite recently, on an uninhabited archipelago off the northwest coast of Scotland called the Shiant Isles. No one knows exactly how the rats reached these remote islands, but it is believed they are the descendants of stowaways that came ashore from sinking ships in the early 20th century. However, over the winter of 2015-16, a rat control project, sponsored by the RSPB, eradicated virtually all rats from the islands over concerns they were negatively affecting the local seabird population. In early 2018, it was announced that the Shiants were officially rat-free.

Black rats have been here in Britain for the last 2,000 years. But not for much longer. With the last stable, substantive colony in the British Isles now gone, the black rat will almost certainly become extinct as a resident British mammal within the next few years. Good riddance to the unwelcome vermin, many might say. But in our mammal-depleted country, having already lost so many species over the centuries, I find it hard to celebrate the loss of yet another.

In the next British Wildlife of the Week, we move from one of our very rarest mammals to what is probably our rarest freshwater fish – the vendace.


  • Jason Woodcock

    With a background in conservation and animal behaviour studies, Jason's passion lies in the natural world. He adores all things nature and enjoys nothing more than spotting rare and interesting species out in the wild. He has also worked in a zoo and knows plenty about keeping the animals inside our homes healthy and happy, too.

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