So what is an invasive species?  An invasive species of animal, insect or plant is one that is not indigenous to the area that it has moved into and is damaging the local eco-systems and habitats, forcing out the native flora and fauna.  It is a big problem in many countries of the world, and there are no easy solutions.

So how does a species get a foothold in another area or country?  It can happen in many ways.  Human migration is one cause.  When people pack up to build a life in a new country or even on a new continent they tend to take their domestic pets and livestock with them; introducing cats, rabbits, dogs, cattle, sheep and goats into regions where they might not have been present before and where they are able to successfully compete against existing species and drive them out.  Some species, like rats and cockroaches, are notorious stowaways and hitch a ride on ships and other transport to destinations around the world.  This is how the great plague in the fourteenth century was spread across Europe; it arrived on the fleas on the rats that were living on the ships that were trading across the Mediterranean and Atlantic coast.  The trade in exotic pets is another vector.  People buy exotic pets, including snakes, spiders, birds, turtles, fish and iguanas, and when they grow too big or they do not want to or cannot care for them anymore, they release them into the wild.  If the climatic conditions are suitable and there is an adequate food supply, they can breed and spread.  

Groups of animals also sometimes escape from zoos, wildlife parks and private collections and form breeding colonies, like the famous colony of wallabies that took up residence in the Peak District of Derbyshire until an extremely cold winter in 1963 wiped the majority of them out.  There are also examples of species being introduced by governments to create a natural predator for a species that is regarded as a pest, either an indigenous species or another introduced species, and for that experiment to go disastrously wrong.  Probably the best example is the cane toad, introduced into Queensland, Australia in the 1930s.  The cane toads were unsuccessful in controlling the pests in the cane fields that they were introduced to deal with, but have bred very rapidly and are now expanding into ever larger swathes of Australia, including the Northern Territory and new South Wales,  depleting local species as they go.

So what is going on in France?  Parts of Belgium and Northern France are being overrun by an invasive species – the Siberian chipmunk.  These cute, striped, friendly rodents began to be imported into Europe from Asia in the 1970’s to be sold as pets and in 1980 seventeen individuals were released into a park in Brussels in Belgium.  They bred successfully and it is currently estimated that there are now more than 100,000 chipmunks living in the wild in France.  A chipmunk can be bought for as little as ten Euros in French pet shops, and the huge numbers of chipmunks in the woods around Paris are attributed to families who bought a chipmunk as a pet and then released them when they did not want them any more. 

Chipmunks are listed on the European Union’s list of 100 most-invasive species, and can be carriers of both rabies and Lyme disease.  Rabies is a virus that is usually spread by a bite from an infected animal or from a scratch that punctures the skin.   The rabies virus attacks the nervous system; causing symptoms of headache, fatigue, high temperature, hypersensitivity, hyperactivity, seizures, hallucinations and paralysis.  Death can be caused by a sudden cardiac arrest or the infected patient may sink into a coma. Lyme disease is carried by ticks that are found on the chipmunks, and is passed on when the tick is transferred to a human and bites them.   The initial symptoms are a rash, fever, headaches, swollen glands and muscle and joint pains.  For some sufferers, they will develop what is known as neuro borrelia between one and five weeks after having been bitten, which affects the central nervous system.  The symptoms can include back pain, nerve numbness, fever, stiffness in the neck, headaches and can develop into a chronic damaging of the nervous system.  In addition, Lyme disease can re-emerge years later as both swelling and discolouration of the skin, Lyme arthritis or inflammation of the heart.

The rapidly expanding population of chipmunks will also compete with local species for food and habitat.  The chipmunks are not nervous of human contact, and as they are easy to approach it makes the chances of someone contracting a disease from them much higher.  There are huge concerns that this highly invasive species will make it to the United Kingdom, threatening both the human population and the native species.  Officials are concerned that they will be bought in pet shops in France and smuggled into the UK, or simply captured in a park or woodland and illegally brought into the country.  In addition, the nearer to the French coast that the chipmunk spreads, the more likely it is that they could find a way onto a train, truck or car that is travelling under or across the Channel and end up in the United Kingdom.

How can this invasive species be stopped from spreading across Europe?  Wildlife experts are pressing for a ban of chipmunks in pet shops, and tourists need to recognise the dangers of trying to take animals across borders illegally.