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Most of us have heard how the introduction of just two dozen rabbits into Australia in 1859 created so much of a problem that within ten years of their release two millions of them could be killed without having any noticeable impact on their population. The rabbits were imported so that immigrant farmers would have something to hunt and eat, but the animals got so much out of control that large areas of southern Australia and some of the flora and fauna that lived in it were effectively destroyed. Many measures have been taken to control the rabbit population; these include rabbit-proof fences, poisoning, trapping and the deliberate introduction of Myxomatosis. And still the rabbits are a problem.

Then there is the case of the so-called Cane Toad. Farmers in Queensland were concerned that their sugar cane crops were being ravaged by the Cane Beetle. Someone heard that a species of toad, bufo marinus, were used with great success in the Caribbean to combat this pest, and a box of 101 of the animals were imported in 1935 and allowed to breed before being released. Oh dear! It was then discovered that the toads, now known as Cane Toads, couldn’t jump very high and most of the Cane Beetles in northern Queensland were out of reach! The result is that Queensland and much of the Northern Territories (and even an area of Sydney) are now infested with a breed of toad which is highly toxic and which breed and spread incredibly fast (each spawning couple can produce from 30,000 to 60,000 eggs!). So prolific are the Cane Toads, that native species of frog (Australia has no natural toads of its own) are dying out because their food sources are being reduced. The toads, which are now one of Australia’s worst environmental problems, are so toxic that they can kill the fish and animals that try to eat them. The toxin on a Cane Toad, for example, can kill a snake so fast that their bodies can remain in the snake’s jaws unswallowed. Fortunately, the toads appear not to be a major problem with humans. Nonetheless, various methods of eradicating the problem are being researched, with a biological one likely to be the answer in due course.

Could such a situation happen in Britain? It already has - and it continues to happen.

I suppose we ought to be used to invasion; we are, after all, the product of a variety of ancient invaders who settled here. But the Norman Conquest didn’t stop our land from being invaded; we have been under attack ever since. However, it is not people who have been invading us, but animals, insects and even plants. Many of these instances are, in fact, manmade.

Take, for example, the Grey Squirrel. This was introduced into Britain from America in the mid-19th century. So successful was this entertaining little creature, because of its larger size and strength, at competing for resources that it has effectively displaced large populations of our native Red Squirrel. It is unlikely that the Red Squirrel population will ever increase substantially, but isolated pockets of them survive in protected areas such as those on the island of Anglesey.

One example which recently featured in the headlines was the introduction of hedgehogs into the Western Isles about thirty years ago. They bred so well that their taste for birds’ eggs led to a decline of up to half of the resident population of a number of resident bird species. From 2003, local people organised a highly controversial annual cull of the hedgehogs , though some were collected and relocated to the mainland where hedgehog populations are in decline. Fortunately, it was announced in February that the culls are to be discontinued in the light of reduced local hedgehog populations and the withdrawal of support by animal welfare organisations.

The number of ‘invasions’ of Britain is staggering:

The Edible Dormouse. This tiny creature, much favoured as a delicacy, was introduced into these islands by the Romans, and can still be found in the Aylesbury area. The Edible Dormouse is one of the earliest of the creatures introduced to these islands by man.

The Wallaby. Visit the island of Inchconnachan and you may come across a red-necked wallaby. These animals, often confused with kangaroos, started with a breeding pair taken from Whipsnade Zoo in 1975. Others reported around the country may be escapees from private collections.

Reeves Muntjac Deer. Colonies of the asian Muntjac Deer exist throughout southern England and are the descendants of escapees from various zoos. They are becoming increasingly common and it is thought that they will soon become Britain’s most common deer.

The North American Mink. Pockets of this highly destructive animal which was imported into this country from the 1920s by fur farmers and which escaped, can still be found in many parts of the country.

The Rose-ringed Parakeet. Visit parts of south London and various other places in the south of England, and you may be surprised to see large flocks of these parakeets which have adapted so well to our climate that their numbers increase annually by an estimated 30%. A sports ground in Surrey was found in a 2004 BBC survey to contain as many as 3,000 of the noisy birds which were originally thought to have been escapees.

The Signal Crayfish. This crayfish was introduced into Britain from America by fish farmers in the 1970s. At some point they escaped and found their way into our inland water systems, and in consequence have all but decimated the resident population of native crayfish. The Signal Crayfish, which is a carrier of the crayfish plague against which the native crayfish have no immunity, can walk overland in its search for a new home and this ability may have aided its spread.

Similarly, the Chinese Mitten Crab has spread from Europe into this country, whether by natural migration or by accidental introduction by, for example, being transported here in ships’ ballast water. Its population in the UK has soared in the last ten years and the crab is now a major concern since it causes substantial damage when it burrows in fragile river banks.

In the plant kingdom, the most notorious invader of Britain is the Japanese Knotweed. This invasive asian plant was imported into Britain by gardeners in the 19th century and is rapidly spreading out of control. Indeed, it is an offence to spread this plant which is difficult to eradicate and causes much structural damage to structures and surfaces in its way.

Another plant introduced by gardeners is the Giant Hogweed, which resembles a giant form of Cow Parsley, is highly toxic. This plant, introduced again for its decorative uses, can cause severe skin inflammations and blisters when touched, and even blindness if minute quantities of the sap get into contact with the eyes. Children especially should be kept away from the plant, and many local authorities and wildlife trusts will post warnings of the presence of a plant whose seeds can germinate up to fifteen years after being dropped.

There are literally hundreds of invasive plants, animals, birds and insects that are thriving in Great Britain and slowly making their way around the country.

These include colonies of tiny European Scorpions which are known to be thriving in various locations around the UK near sea ports and freight depots. These harmless arachnids are thought to be accidental escapees from ships and cargoes arriving in the country. Then there are the various spiders that occasionally crawl out from banana fronds. In the main, their bites may be painful but rarely fatal, though medical advice should be sought in every case.

And then there are ...

But, perhaps, you have read enough already.

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