A flatworm that overwhelms snails in a “gang attack” and has caused many extinctions when introduced to other parts of the world has now arrived in Europe. Urgent action is necessary to save wild British snails – the UK Government should close the borders to pot plants.
Buglife is a strong and positive advocate for bugs of all shapes, sizes and habits. We are forgiving of many of their foibles and indeed we big-up the good sides of persecuted animals such as wasps and spiders – dispelling prejudice and educating the public.
However, there are some bugs that we are less keen on – bugs in places where they should not be that are causing damage to wildlife. We call these bugs ‘harmful invasive non-natives’.
A healthy ecosystem is like a mechanical clock, thousands of whirring cogs each different, but each contributing to keeping time. Some of the cogs are restricted to a particular ecosystem, while others can function harmoniously in a range of ecosystems – a lapwing can thrive on a mountain pasture or a coastal saltmarsh. Individual cogs are prevented from becoming too dominant because other cogs have evolved to check and balance their activities and the cogs have cohabited ecosystems for millions of years, evolving ways to succeed alongside each other – each has its own niche. 
In an ecosystem a species of caterpillar is prevented from eating all the scabious flowers in a meadow because a parasitic wasp has evolved that thrives when the caterpillar’s numbers increase and they become easy to find, this reduces the numbers of caterpillars reaching maturity. The blackbirds and robins in my garden do not eradicate each other because they have evolved to nest in different places and eat different things at different times of day.
However, this happy stability can be turned upside down when a species is introduced from a distant ecosystem. The introduced species has not encountered plants and animals like those native in this ecosystem for millions of years. They have no strategy to deal with the invader. Released from its shackles of parasites and evolved coping strategies the invasive non-native can become harmful, eradicating native species and unbalancing ecosystems. It’s as if the cog in the clock grows and grows, spinning faster and faster, tearing up the resident cogs and upsetting the keeping of time.
Harmful invasive non-native species are one of the major world causes of biodiversity loss and their activities can also be very damaging to people as they invade and cause unwelcome changes in agricultural ecosystems and even in our homes. I blogged recently about one of the invasive species that is damaging native biodiversity – the American Signal crayfish (technically a problem with two invasive species because the American crayfish are carriers of another invasive species, the Crayfish plague (Aphanomyces astaci), that wipes out native crayfish).
Not all introduced species become invasive and the amount of harm caused to agriculture, garden plants, wildlife and the economy varies widely from one species to the next. But each new species that gets introduced is a risk. Sometimes the record of that animal in other parts of the world where it has been introduced gives a strong clue as to the likely damage it would cause in the UK.
One of the big areas of risk is the international trade in pot plants. It is practically impossible to sterilise the soil in a pot plant, no matter how toxic the chemicals that it is fumigated with, it only takes one or two eggs in a pocket of air deep in the soil to survive and a potentially devastating invasive species has crossed over a border and threatens a new country.
The immersion of pot plants in hot water is a proposed biosecurity measure, but it has not been adequately tested and has never been implemented.
The international pot plant trade is the likely source of all the following species:-
Harlequin ladybird (Harmonia axyridis) – that consumes our native ladybirds and causes a nuisance in people’s houses in the autumn.
Oak processionary moth (Thaumetopoea processionea) – that has very irritating hairs that stimulate the Forestry Commission into spraying woodlands with toxic pesticides that damage ecology.
New Zealand flatworm (Arthurdendyus triangulatus) – a predator of our earthworms that has spread into the wild in parts of Northern England, Scotland and Northern Ireland. Its impacts have been particularly heavy on our most ecologically important earthworm the Lob worm (Lumbricus terrestris).
Australian flatworm (Australoplana sanguinea) – a predator of our earthworms in gardens. 
Lily beetle (Lilioceris lilii) – a shiny red beetle that people like, until it eats all their lilies.
Rosemary leaf beetle (Chrysolina americana) – a frankly beautiful beetle, but not all rosemary growers agree with me.
Spanish slug (Arion vulgaris) – a huge slug spreading through Britain’s gardens and causing havoc.
Girdled snail (Hygromia cinctella) – common and widespread in southern England and moving up into Scotland, but not yet known to be a problem species.
Australian landhopper (Arcitalitrus dorrieni) – a shrimp with the same story as the Girdled snail.
Light brown apple moth (Epiphyas postvittana) – one of the commonest garden moths in many areas but so far only causing minor problems – imported from Australia.
This is only the start, there are many more species already infesting the pot plant trade, or likely to do so, which pose a very high risk to UK wildlife and agriculture, including:-
Asian hornet (Vespa velutina) – a bee eating wasp already destroying bee populations in France.
Argentine ant (Linepithema humile) – one of the worst invasive species in the world – eliminates native ant species and damages ecosystems.
And now a new risk to British wildlife from the pot plant trade has been identified. New Guinea flatworm (Platydemus manokwari) has been found in France and experts are calling for action to prevent its spread now! 
The New Guinea flatworm is a horror that has destroyed populations of native snails across the Indo-Pacific. It is considered to be the a cause of the extinction of native land snails on several Pacific and Pacific Rim islands and is one of the major threats to the famous Partula tree snails.
New Guinea flatworms are particularly effective at causing the extinction of species because they are capable of eating all the available prey and then fasting for months or years. While fasting the flatworms digest their own tissues, shrinking to a fraction of their former size. All the time they are alert to the distant scent of the next snail to arrive in the vicinity. When they smell a snail they home in, overwhelming it by sheer numbers in a “gang attack”.
The New Guinea flatworm occurs in a wide range of climates – alpine, sub-alpine, cool temperate, warm temperate and tropical – so there is no reason to believe that it won’t thrive in Northern Europe.
If we are to save British wildlife from these and other, less well understood, invasive perils action is required now. Governments can protect the environment, just as the Australian and New Zealand governments do, by preventing the importation of high risk biological material such as pot plants.
There is no need to import pot plants into the UK – horticulturalists here are quite capable of growing our own pot plants and selling them to the domestic market. Until there is a proven way to sterilise pot plants and this is implemented the UK Government should take effective action and close our borders to the dangerous trade in pot plants.
New Guinea flatworm (Platydemus manokwari) – Justine J, Winsor L, Gey D, Gros P, Thévenot J. (2014) The invasive New Guinea flatworm Platydemus manokwari in France, the first record for Europe: time for action is now. PeerJ 2:e297 http://dx.doi.org/10.7717/peerj.297
