- Features
June 26, 2026

- Features
June 26, 2026

Britain’s accidental wildlife

From terrapins to tanuki, we discuss how invasive non-native animals became established in Britain and why responsible ownership matters.

When pets go wild

When you think of invasive non-native species, grey squirrels or Himalayan balsam spring to mind.

But what about a terrapin basking on a log in your local pond? A flock of bright-green parakeets screeching through a city park? Or even a wallaby hopping through the countryside?

It may sound unlikely, but Britain is home to a surprising number of non-native animals that owe their presence to people. Some escaped, some were released, while others were introduced deliberately. Many never establish themselves in the wild; however, history shows that some do.

Is every non-native species a problem?

The simple answer is no.

Some species introduced to Britain have become established without causing significant harm and, in some cases, have even brought benefits.

Little owls, for example, were introduced to Northamptonshire in the late nineteenth century and are now widespread across England, Wales and southern Scotland. They have become a familiar and much-loved part of the countryside.

Pheasants have an even longer history, having been introduced to Britain during the 11th and 12th centuries. Today, when released in line with sustainable gamebird releasing guidelines, their presence contributes to the creation and management of valuable habitats such as woodlands and game covers, supporting a wide range of other wildlife. Shooting also delivers significant social and economic benefits to rural communities.

The concern is not simply that a species is non-native. It is when a species has serious negative impacts on people, the economy or the environment. These are the species formally recognised as invasive non-native species, and once they become established, managing them is usually far more difficult than preventing their release in the first place.

How a caged bird conquered London

Few birds divide opinion quite like the ring-necked parakeet.

Their unmistakable green plumage and noisy calls have become a familiar feature of parks and gardens across parts of southern England, particularly around London.

They are not native to Britain. Instead, today’s population is thought to have grown from escaped or released captive birds over many years.

The British Trust for Ornithology estimates there are now around 12,000 breeding pairs in Britain.

Their success shows how a handful of escaped birds can eventually establish a thriving wild population.

The terrapin that outgrew the fish tank

Terrapins became popular pets during the 1980s and 1990s, but many owners soon discovered that the tiny turtles sold in pet shops grew much larger than expected and required specialist care. Some were released into local ponds and lakes instead.

A recent Turtle Tally UK survey recorded 1,387 turtles and terrapins living in the wild between 2019 and 2023, with sightings reported across England, Wales, Scotland and Northern Ireland.

Britain’s climate means they rarely breed successfully, but individual terrapins can survive for many years, competing with native wildlife for food and basking sites.

It is perhaps the best-known example of why releasing unwanted pets into the countryside is never a good idea.

When escapees become residents

Not every non-native animal arrived through the pet trade. Some escaped from ornamental collections or private estates before establishing wild populations.

The Egyptian goose is one of the best examples. Introduced centuries ago as an ornamental bird, escaped individuals established breeding populations that have expanded rapidly. The British Trust for Ornithology reports that breeding numbers have increased by almost 2,000 per cent since 1995.

Mandarin ducks followed a similar path. Once confined to ornamental collections, they are now established across many parts of England, with breeding numbers increasing by around 580 per cent over the same period.

These birds are now a familiar sight in many parts of Britain, demonstrating just how difficult it can be to predict the long-term consequences of introducing animals outside their natural range.

The ones we don't want to establish

Some non-native species have yet to gain a foothold in Britain, but they remain a concern.

The raccoon dog, or tanuki, is native to East Asia but has established populations across parts of mainland Europe. It is recognised as a high-risk invasive species because of its potential impact on native wildlife.

There is currently no established population in Britain, although occasional sightings continue to make headlines.

Raccoons are another species identified by experts as posing a future risk should escaped or released animals begin breeding in the wild. The lesson is clear – preventing introductions is far easier than removing a species once it becomes established.

Wait… wallabies?

It might sound like an April Fool’s joke, but wallabies really do exist in the British countryside.

Most are thought to have escaped from wildlife parks or private collections. Small localised populations have been recorded in parts of Great Britain, while the Isle of Man supports an established population estimated at around 1,700 red-necked wallabies.

They remain unusual, but they show that captive animals can survive and breed if conditions are right.

Making sure ferrets come home

Ferrets occupy a different place in this discussion. For many people involved in rabbit control, they remain an effective and valuable working animal. Responsible owners always make sure their ferrets are recovered after use, often using locator collars and good fieldcraft.

That matters because feral populations can cause problems in sensitive environments. On Rathlin Island, Northern Ireland, feral ferrets established after animals escaped or were abandoned became a serious threat to internationally important seabird colonies before a successful eradication programme removed them.

Good husbandry protects both the welfare of the animal and the wider environment.

History repeating itself

Escaped pets are only part of the story. Grey squirrels were introduced from North America during the late nineteenth and early twentieth centuries as ornamental additions to parks and estates. Today they are widespread across much of Britain, damaging woodland through bark stripping and contributing to the decline of native red squirrels through competition and disease.

Reeves’s muntjac tell a similar story. Originally imported from China and kept in collections, animals escaped and established breeding populations. They are now widespread across large parts of England and continue to spread into new areas, browsing woodland plants and affecting natural regeneration.

Neither species arrived through the modern pet trade, but both demonstrate the same lesson. Once a non-native animal becomes established, the consequences can last for generations.

What if you can no longer keep an exotic pet?

Circumstances change, but releasing an animal into the wild is never the answer.

If you can no longer care for an exotic pet:

contact the breeder or retailer to see if they can help
speak to a specialist rescue organisation or rehoming charity
seek advice from your vet or the relevant species organisation

Taking the time to find a safe alternative protects the welfare of the animal and helps prevent future problems for Britain’s wildlife and habitats.

Keeping wildlife wild

Most pet owners are responsible and would never deliberately release an animal into the wild. Equally, the vast majority of people keeping ornamental birds, exotic animals or working ferrets understand the responsibility that comes with ownership.

However, many of Britain’s best-known non-native species can ultimately be traced back to animals that escaped, were released or were introduced without a full understanding of the consequences.

Invasive Species Week reminds us that preventing the next invasive species problem often starts with simply making sure captive animals stay where they belong.