nQuagga/Zebra Mussels – Spread to the UK in ballast water, these molluscs reproduce prolifically and can clog up piping. They are filter feeders and remove so much plankton from the water that the whole balance of the aquatic environment can be thrown, resulting in collapses of populations of native species. nRose-ringed Parakeets – They escaped in to the UK in late 1960s. They are largely a problem in SE England where quite a population has built up. They out-compete native species for nest-holes in trees. nAmerican Mink – They escaped or were liberated from fur farms in the 1960s. They have since become a real problem in the UK as they will predate anything they are big enough to catch, which includes ground-nesting birds and most significantly the Water Vole population, which has been devastated. nKiller Shrimp– These are two species of shrimp of the genus Dikerogammarus that due to their greater size than similar native shrimps and voracious appetites have the potential to devastate aquatic communities by basically eating anything they can get hold of including fish fry. Not sure about Gwent, but they certainly occur in Cardiff Bay. nAsian Hornets – A species which has received much media coverage in the last couple of years. They are a real problem in France, devastating local honey-bee populations. To date there have been only 13 sightings in the UK, with eight of these in 2018. nInvasive Garden Ant – Not one I had previously heard of, but first discovered in the UK in 2009. They form far bigger colonies than our native ants and can thus outcompete them. They’re predicted to potentially be a big problem. nAmerican Signal Crayfish – Imported into the UK in the 1970s as a food source, they escaped in to our waterways. They have decimated out native White-clawed Crayfish population by outcompeting them and also spreading the deadly Crayfish Plague. They have also had a detrimental impact on many other native freshwater species and have caused bank instability with their burrows. nTopmouth Gudgeon – They were introduced into the UK in 1984 and have since spread to a number of sites. They are only small fish species, however they are problematic because they breed rapidly and in great numbers, quickly producing large densities that then feed on the eggs of other fish species. The Environment Agency has been working to eradicate this species before it spreads to too many sites. nGrey Squirrel – They are familiar and widespread, having been introduced into the UK in the 19th century. They are a real ecological and commercial problem, responsible for the loss of our native Red Squirrel from much of the UK through competition and the spread of the deadly Squirrel Pox, to which they are themselves immune. They are also a real problem in forestry through their habitat of bark stripping younger trees, which can deform or kill them. I don’t need to tell you they are widespread! nMuntjac Deer – These small deer were brought to Woburn Park in Bedfordshire in the early 20th century. They have since escaped and spread to many parts of the UK. They can be a real problem in native woodland as they will eat off all new growth, preventing new tree growth both from coppice and new seedlings with long- term implications for the health of the woodland. They are present in Gwent and alongside the Fallow Deer are a considerable ecological issue, particularly in the Wye Valley area.

n New-Zealand and Australian Flatworms – There are approximately 10 non-native flatworm species in the UK with these two regarded as being problematic as they prey on our native earthworm populations with resultant impacts on diversity and soil structure. The New-Zealand Flatworm is considered to be the worst offender of the two.

A number of these INNS are listed on Schedule 9 of the Wildlife & Countryside Act 1981, together with various other animals. This legislation makes it “illegal to release or allow to escape into the wild any animal which is not ordinarily resident in Great Britain and is not a regular visitor to Great Britain in a wild state, or is listed in Schedule 9 to the Act”.

These species are such a problem because they out-compete our native fauna for resources such as food and breeding sites, they can spread diseases to which our native fauna has no resistance and prey on our native fauna. The result is a reduction in diversity with knock-on negative effects elsewhere within the food-chain. It all sounds a bit depressing, and there are very real concerns that need to be addressed regarding INNS. There are things that can be done with some positive outcomes.

The Environment Agency have had good success in their work to remove Topmouth Gudgeon and a school of thought is that the reintroduction of native Pine Martens could control Grey Squirrel populations with resultant benefits for Red Squirrels and on the Gwent Levels, properly planned Mink control operations can reduce populations to a level where successful Water Vole reintroductions can be carried out.

We should remember that it’s not the INNS animal’s fault that they are in this country and causing problems, that is almost exclusively our fault. The animals are just doing what comes naturally and exploiting the new habitats they find themselves in as best they can. With this in mind any control measures or culls must only be carried out where strictly necessary and be as humane as possible. We must then learn the lessons of what can happen introducing species in to the UK and take necessary measures to prevent this happening. There are various things that can be done to prevent the spread of INNS, for example aquatic species are a particular problem, so to prevent spreading individuals, particularly anglers, should use the check, clean and dry approach to equipment such as nets when moving between different waterbodies to prevent the spread of organisms. Also, sightings of INNS should be reported in accordance with GB Non-native Species Secretariat guidance -

To find out more about the work of Gwent Wildlife Trust visit:




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