We use cookies on this website. By using this site, you agree that we may store and access cookies on your device.

Invasive Species

The text in this section is based on information provided by Invasive Species Ireland, a joint initiative by National Parks & Wildlife Service and the Northern Ireland Environment Agency. 

 Definition

Invasive species are species that have been introduced (deliberately or accidentally) by humans and have a negative impact on the economy, wildlife or habitats of Ireland and Northern Ireland. After habitat loss, invasive species are the second biggest threat to biodiversity worldwide, and the biggest threat on islands.  They can also be called "alien invasive species".  The UN's Convention for Biological Diversity (CBD) defines alien invasive species as being alien or non-native "species which becomes established in natural or semi-natural ecosystems or habitat, is an agent of change, and threatens native biological diversity"

Invasive species are one of the main drivers of biodiversity loss across the globe.

Ecosystems provide a variety of services to us for free and these bring many benefits to society and the economy. There are four main categories: provisioning, such as the production of food and water; regulating, which includes the control of climate and disease; supporting, for example, nutrient cycling and crop pollination; and cultural, such as spiritual and recreational benefits.  Invasive species can impact on the ability of nature to provide these services resulting in increased economic costs and environmental damage.

The impacts of invasive species on biodiversity are widely demonstrated and can occur in all habitats. For example:

  • Outcompeting native species for resources (grey squirrels)
  • Reducing native biodiversity by grazing on native flora (muntjac deer)
  • Predation on native species and their young (Feral ferret)
  • Altering habitats which can lead to flooding (Aquatic plants blocking rivers, canals and drainage channels)
  • Introduction of parasites (eel swimbladder nematode) and pathogens (squirrel poxvirus) which were not previously found here and against which our native species are not adapted to cope.
  • Dilution of native gene pools by interbreeding with native species (ruddy duck).

    A summary of the impacts of invasive species in Ireland can be found in the Invasive Species in Ireland report.

Invasive species have been estimated to cost the European economy €12.7 billion each year.

Estimating the economic impact of an invasive species is difficult but it is vital to know the cost of controlling species and managing their impacts to inform management decisions. Invasive species are estimated to cost the United States economy in the region of $137 billion per year (Pimental et al. 2000). In Europe this figure stands at approximately €12.7 billion/year (Kettunen et al. 2008). These figures are likely to be underestimates as there is a limited availability of documented costs.

Financial costs in response to invasive species can occur as a result of prevention, management, mitigation, loss of productivity or as the result in the loss or decline of an economically important species. These economic impacts can be incurred by anyone on individual, collective and international levels.

Some countries such as New Zealand consider invasive species management as part of biosecurity.  Biosecurity in Ireland has traditionally covered the areas of plant and animal health, however invasive species could be considered to be the third strand of biosecurity.

Biosecurity plans have been drawn up for areas such as lake catchments with the aim of preventing invasions and putting in place contingency plans.  Invasive Species Ireland takes a biosecurity approach to the development of Invasive Species Action Plans and has links to the plant and animal health regimes on the island of Ireland.

As well as having impacts on the environment and the economy, invasive species may impact on our lifestyles. There are a wide range of activites than can unintentionally spread invasive species such as gardening, boating, angling and the keeping and trade of pets.

Invasive species have the potential to disrupt these activities as they transform the environment around us.  For example:

  • Invasive plants can take over a garden and spread into neighbouring properties
  • Invasive plants can prevent angling and access to rivers and lakes
  • Invasive species can restrict boating by interfering with navigation and colonising boat hulls and marinas
  • Pets can escape and become established in the wild

Invasive Species Ireland have advice on how you can prevent the spread of invasive species in their ‘What can I do?’ section.

Invasive Species Ireland's "Most Unwanted" list

Invasive Species Ireland's Management Toolkit, including the Amber List of established and potential invasive species

The Convention for Biological Diversity's section on Invasive Alien Species 

The National Biodiversity Datacentre's National Invasive Species Database, including species alerts and updated distribution maps.

The Central Fisheries Board, Control of Aquatic Invasive Species in Ireland (CAISIE) website