logo: Invasive Species WeekInvasive Species Week


From 13 Ė 17 May, organisations across Britain are taking part in Invasive Species Week to raise awareness of invasive species and their impacts on us all. Anyone working in the field is likely to have encountered invasive species, but may not realise how easily they could be helping to spread them.


What are invasive species?

Around 2,000 non-native plants and animals from all over the world have been introduced to Britain by people, and the number is increasing each year. Most are harmless but 10-15% have become invasive and have a negative impact on our environment, cost the British economy over £1.7 billion a year, and can even harm our health and way of life. Once established they are extremely difficult to manage and the damage they cause is usually irreversible.

Floating pennywort clogs waterways preventing navigation and increasing the risk of flooding. Image: Phil Harding, Environment Agency.

Floating pennywort clogs waterways preventing navigation and

increasing the risk of flooding.

Image: Phil Harding, Environment Agency.


Some have been deliberately introduced to the wild, but many others have been spread unintentionally, for example between waterbodies on sampling equipment, boats or angling gear or from gardens through irresponsible disposable of garden waste.


The impacts of invasive species are felt across a wide range of important habitats and native wildlife.

Lakes, rivers, streams and other freshwaters are particularly vulnerable to invasion by species such as floating pennywort, originally introduced as a pond plant. In the wild it forms dense mats which grow up to 20cm a day under the right conditions; these affect oxygen levels in the water, crowd out and kill off native wildlife, and damage habitat. Floating pennywort can regenerate from a tiny fragment and survive over two weeks out of water in damp conditions. In 2017 the Environment Agency removed over 1,000 tonnes, mostly from the Thames, Cam and Ouse River catchments.

Woodlands are a key part of our landscape and cultural heritage and home to some of the countryís rarest wildlife, but the biodiversity they support is threatened by species such as rhododendron. A dense sea of purple flowers may look attractive in bloom, but once rhododendron has become established, few native plants in that area will survive. Only trees which are able to grow above the rhododendron canopy will persist and when those die they cannot be replaced as seedlings are unable to establish under the lightless canopy. Each large rhododendron bush can produce several million seeds per year, which can remain viable in the soil for several years.

American mink attacking a gannet chick, classified as a vulnerable species by the IUCN. Image: John W Anderson.

American mink attacking a gannet chick, classified as a vulnerable

species by the IUCN. Image: John W Anderson.


Britain is surrounded by small islands which are an important habitat for rare birds. The impacts of invasive species are often far worse on small islands as native wildlife has evolved in isolation from predators, competitors and diseases. As a result native species are less able to compete and defend themselves in the face of new threats. The introduction of non-native mammalian predators including rats, mice and mink to islands all over the world has contributed to declines and extinctions of a number of rare bird species.


What can I do to help?

Follow a good biosecurity routine when working in the field to reduce your risk of spreading invasive species:

  • Arrive at the site with clean footwear and vehicle.
  • Ensure footwear is clean (visually from soil and debris) before leaving - use any facilities provided.
  • Ensure vehicle is kept clean - remove any accumulated mud before leaving site.
  • Minimise access and if practical do not take vehicles onto premises, keep to established tracks and park vehicles on hard standing.
  • Where possible avoid areas of livestock and areas with known disease issues.
  • Plan visits so that the most risky visit is last.

Free online biosecurity training for is available from www.nonnativespecies.org/elearning.


There are simple things that everyone can do to help protect the environment:

  • If youíre an angler, canoeist, boater or similar, Check Clean Dry your kit after leaving the water to avoid spreading invasive species between waterbodies. Itís even more important if youíre abroad as you could bring back new plants and animals.
  • Be Plant Wise when planning a clear out of your garden, pond or aquarium, dispose of plants responsibly and donít dump them in the wild.
  • Take care of pets, never release them or allow them to escape into the wild. Itís cruel and could harm other wildlife.
  • Look out for Asian hornet. Find out more and report sightings at www.nonnativespecies.org/alerts/asianhornet or download the Asian Hornet Watch app.
  • If you enjoy being outside why not join a Local Action Group working on invasive species management. Contact nnss@apha.gov.uk to find your nearest group.


Find out more about Invasive Species Week by visiting www.nonnativespecies.org/invasivespeciesweek or on Twitter @InvasiveSp.