Non-native species are plants or animals that have been introduced (deliberately or accidentally) by human activities into an area outside of their natural range. Over 2,000 plants and animals have been introduced to Britain from all over the world by people.
Many of the plants we grow for food or to decorate our gardens, and many of the animals we farm or keep as pets are non-native and can provide a positive value to our lives.
However, around 10-15% of non-native species have the ability to spread and become dominant. They cause to harm wildlife and the environment, are costly to the economy and can even impact on our health and way of life – these are invasive non-native species (INNS).
Please read and note the below, compiled by SEPA (Scottish Environmental Protection Agency). They include both species that are already here, and a menace, and also those species we are currently threatened with. Obviously, we all have a part to play in preventing their spread.
We all have a role to play to prevent the spread of INNS. It is especially important for aquatic species because, once they have established in the water, they are very costly and difficult and, in most cases, impossible to eradicate. Many invasive plant species can clog watercourses, making them inaccessible for water sports.
The best thing we can do is to Check Clean Dry our equipment and clothing every time we leave the water so that we don’t accidentally carry an INNS to the next place we visit. Find out more about environmental best practices on the SCA Environment page.
These are examples of species that are already causing problems elsewhere, including England, so we need to be especially vigilant to prevent them from arriving in Scotland.
Floating pennywort (Hydrocotyle ranunculoides)
Floating pennywort (also called water pennywort) grows in fresh water. It can grow up to 20 centimetres a day, blocking out light and reducing the oxygen for other plants and animals. It blocks waterways, preventing access to the water and increasing the risk of flooding.
Floating pennywort:
Water primrose (Ludwigia grandiflora)
Water primrose is a highly invasive freshwater weed from South America. It has become a serious problem in France where it blocks waterways and overgrows ponds and lakes. It has only recently started to be found in Britain. but if it were to establish widely could cost as much as £242 million to manage.
Water primrose:
• grows on the banks of rivers and lakes and floating on the surface of the water
• has a flower with 5 bright yellow flower and distinctive seed pods
• has a thick fleshy stem Has leaves which range from long and thin to almost completely round
Killer Shrimp (Dikerogammarus villosus)
Killer shrimp is a freshwater species. It is a predator of native shrimp and other native species, including fish eggs. It can disrupt whole ecosystems through predation and its impact across food chains. Parasites carried by killer shrimp could reduce fish stocks.
Killer shrimp:
• have a tail with distinctive cone-shaped bumps
• usually have striped backs, but can be more uniform in colour
• can grow to 30 mm long, larger than native shrimp, but are more commonly 10 to 20 mm.
Find out more about killer shrimp
These are examples of species recorded in Scotland. In some cases they are established locally, but none are widespread across Scotland so it is possible to protect uninvaded waters. We need to take care not to spread them to other parts of Scotland.
New Zealand pygmyweed (Crassula helmsii)
New Zealand pygmyweed grows in freshwater ponds, lochs, reservoirs, canals and ditches and can spread out onto damp ground. It can cover small ponds to a depth of 0.5m or cover the margins and bed of larger deeper waterbodies over many square metres. It can prevent recreational and commercial activities and may cause extensive declines in native plants.
New Zealand pygmyweed:
• has yellowish-green opposite succulent leaves that are < 20mm long
• has solitary white or pale pink flowers
Zebra mussel (Dreissena polymorpha)
Zebra mussels are found in freshwater rivers, canals and lochs. They can block pipe-work and affect lock gates. They can also smother native species and rapidly take nutrients from the water, altering ecosystems.
Zebra mussels:
• are very small - usually about 30 mm in length but can grow up to 50 mm
• have light and dark bands of colour, usually blue or brown and yellow-white
• are a distinctive 'D' shape
• attach, usually in groups, to anything solid underwater, like masonry, stones or tree roots
North American signal crayfish (Pacifastacus leniusculus)
Signal crayfish are found in freshwater streams, canals, rivers, lochs and ponds, and are also able to survive in brackish water. They cause declines in diversity and richness of aquatic communities. Commercial fisheries have been affected by predation of fish eggs and competition between crayfish and salmonids for refuges. Burrowing by crayfish can cause erosion of riverbanks and destabilise structures built at the edges of rivers.
Signal crayfish:
• is lobster-like in appearance
• reaches a maximum size of 16-18cm
• have red undersides to the claws, with a small turquoise/white blotch on the upper surface at the claw hinge
Carpet Sea-squirt (Didemnum vexillum)
Carpet Sea-squirt is a marine species recorded in coastal marinas and adjacent shallow artificial structures but can grow on natural cobble or gravel seabed to 80m depth, in tide pools on shore, in seagrass beds and on aquaculture installations. Colonies can spread to extensive coverage of seabed, potentially smothering species living in gravel and affecting fisheries and shellfish industries.
Carpet sea-squirt:
• is pale orange, cream or off-white colonies forming extensive, thin (2-5 mm) sheets and can form long pendulous outgrowths
• has a firm, leathery texture and veined or marbled appearance
• has numerous small pores in surface close when colony disturbed to produce tiny whitish spots
Find out more about carpet sea-squirt
These are examples of species present on land in Scotland that you should look out for as you access the water – take care not to transport seeds or fragments of plants.
Giant Hogweed (Heracleum mantegazzianum)
Giant hogweed is especially abundant by lowland streams and rivers, but also occurs widely on waste ground and in rough pastures. It grows on moist fertile soils, achieving its greatest stature in partial shade.
The sap can sensitize human skin to ultra-violet light, leading to severe blisters. Affected skin may remain sensitive for several years. The plant is also a vigorous competitor, producing almost pure stands which exclude native vegetation and hinder access to the water.
Giant hogweed:
• has flowering stems typically 2-3m high
• bears ‘umbels’ of flowers up to 80 cm in diameter
• has leaves often 1m or more in size
Himalayan balsam (Impatiens glandulifera)
Himalayan balsam grows in moist and semi-shaded damp places, predominant on banksides by slow-moving watercourses. It spreads rapidly on soft banks of waterbodies, forming extensive monoculture stands to the exclusion of most other plants.
Himalayan balsam:
• is an annual herb
• has stout succulent, reddish-translucent hollow stems up to 2.5m tall
• has leaves 5-18cm long and 3-7cm wide
• has deep purplish-pink to white flowers with a distinctive strong balsam smell
