When Dr Silviu Petrovan identified a Colombian tree frog in some imported roses in a florist’s shop in Sheffield, and then a reed frog from South Africa in a shipment of aquatic ornamental plants, it got him thinking – what other species were hitching rides in pot plants and cut flowers coming into Europe from abroad and what damage were they doing?
Several years later and now we know at least a little bit more about this multi-billion-pound trade – and it’s not good news.
For a start, it’s not just or even mainly relatively large animals such as amphibians and reptiles that are coming into the country unnoticed, according to a paper published by Petrovan and colleagues from around the world in the journal BioScience.
Data obtained from the Department for Environment, Food and Rural Affairs (Defra) by Petrovan and his colleagues shows that customs officers in the UK are coming across mainly invertebrates.
The largest volume of interceptions in Britain involved a small insect called the silver leaf whitefly, which probably originates from India and is described as "one of the most economically important agricultural and horticultural pests in the world” – it has the potential to be a major pest of salad crops such as tomatoes and cucumbers grown in greenhouses.
And as Prof William Sutherland, who was involved in the study, points out, it would be impossible for officials to spot and identify all the tiny insects and other pathogens such as fungi that are coming through in these shipments. “It’s inconceivable that they can thoroughly check an import of a million roses from Kenya,” he says.
The whitefly is not causing any damage in the UK yet, but according to Petrovan, other species have been spread by this trade and become established. The Italian wall lizard, for example, is now found over much of Europe and even parts of the USA and Canada as a result of the pot plant trade.
“There are several records of them arriving with cargo into Britain,” says Petrovan. “A large number that arrived with a stone shipment from Italy were luckily discovered in Buckinghamshire and eradicated on time a few years ago.”
What can governments do about this growing threat? Petrovan says governments across the world need to make interception data publicly available so that researchers such as them can better understand which and how potential alien species are entering countries.
The results of not worrying about this trade can be seen in our countryside today – Japanese knotweed and Himalayan balsam were originally introduced as ornamental plants, and today they and other non-native species cost the UK economy an estimated £4 billion a year.
Main image: European tree frogs (not the species found in Sheffield) are often accidentally imported with flowers coming into the Netherlands, say the study authors/University of Cambridge
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