Alien species are animals, plants, fungi and micro-organisms that have been introduced to a new natural environment from other parts of the world through human intervention. The number of alien species is on the rise in Europe, totalling more than 12,000 at the moment. Many of these species are brought into Europe intentionally, for their beauty, usefulness or commercial value. Others arrive by accident, for example, as contaminants of other goods or as hitchhikers on boats or automobiles.

Invasive Alien Species (IAS) are alien species whose introduction and spread cause serious negative environmental consequences. Fortunately, not all alien species cause harm to their new environment: the vast majority experience difficulties surviving, growing or reproducing. Roughly 10 to 15% of alien species arriving in Europe become invasive and locally over-abundant, often as a consequence of a lack of predators and parasites that would normally keep them in check.


Invasive alien species pose a huge threat to Europe's biodiversity. They may cause the extinction of native species and alter the functioning of entire ecosystems. IAS can also cause major economic impacts as they can damage infrastructure, obstruct transportation, and reduce yields from agriculture, forestry or fisheries. Additionally, some species cause serious health problems for both humans and animals, such as allergies and disease transmission. The cost to the European economy is estimated to be at least 12 billion per year. As more and more of these species are entering Europe and, by definition, spreading rapidly, the costs are predicted to increase rapidly and are expected to be exacerbated by climate change. Moreover, the costs associated with IAS rise exponentially if the species is not dealt with immediately.


Invasive alien species do not respect administrative borders. Once a species is established in one country, it can easily spread to neighbouring countries through natural dispersal or (un)intentional human intervention. Also, prevention and management measures undertaken at national level may be undermined by lack of similar actions adopted in neighbouring countries. Clearly, a European approach to the problem of invasive alien species is required.

To this end, new legislation on IAS was introduced in the European Union, establishing a coordinated EU-wide framework for actions to prevent, minimise and mitigate the adverse impact of IAS. It is based on three types of measures, each tackling IAS according to their level of occurrence in Europe:

  • Prevention: measures to prevent intentional and unintentional introduction and spread of IAS into and within the European Union territory.
  • Early warning and rapid response: an obligation for Member States to detect the presence of IAS as early as possible and take measures to prevent establishment and further spread on their territory.
  • Management of widespread species: an obligation for Member States to manage already well-established IAS on their territory to prevent further spread and minimise harm.

At the core of the EU Regulation is a list of IAS of Union concern. This list represents a subset of IAS that all Member States agree to take action on. These species can either be already present in Europe or absent, but expected to enter the EU territory without action.

Want to know more? Read this brochure on Invasive Alien Species, published by the European Commission.