A large rat-eating snake from Europe is breeding in central London – just one of more than 50 foreign reptiles and amphibians seen living wild in the capital area in recent years.
At up to 6ft 6ins long, the predatory Aesculapian snake, which feeds on rats and other small mammals, is bigger than any native British reptile, but although it is found across the continent from France to Russia, it has never been a resident of Britain.
Yet now a small population of Zamenis longissimus is flourishing in London NW1, a stone's throw – or a snake's slither – from one of the capital's smartest addresses, Primrose Hill.
There are thought to be 30 or more of the snakes, descendants of a small group released in the 1980s, living and breeding in the undergrowth alongside the Regent's Canal at the edge of Regent's Park, near London Zoo. But the actors, media types and rock musicians of Primrose Hill can take comfort in the fact that although their new neighbours are big, they are not venomous.
They are one of many exotic and non-native presences from the reptile and amphibian world which have been recorded living wild within the Greater London area – roughly the area inside the M25 – according to a detailed report from the London Natural History Society, which is featured in the current issue of British Wildlife magazine.
No fewer than 51 alien taxa – the technical term for species and sub-species counted together – have been observed, split between 30 reptiles, ranging from snapping turtles to red-eared terrapins, and 21 amphibians, from American bullfrogs to midwife toads.
In particular, there are no fewer than 22 different types of freshwater terrapin – mostly American species and hybrids – at large in park ponds and lakes and rivers in probably every London borough, originating from a pet craze which followed the American animated children's TV series Teenage Mutant Ninja Turtles of the late 1980s and early 1990s.
"On the back of the TV programme the North American terrapin became the latter-day hamster," said Tom Langton, a conservation ecologist who is one of the authors of the report.
"It was a cool pet. But people didn't realise that these animals grow slowly and can live up to 50 or 60 years, not the six months to two years when I can remember my hamsters dying.
"The majority of these animals were dumped when people could no longer cope with them. Teenagers leaving home left a trail of terrapins to be put in the local river or the local park."
The second biggest group are several species of "green" or "water" frogs from Europe, including the marsh frog, the pool frog and the edible frog, which Mr Langton said had been spread "massively" by the pet trade. They presented a potential threat of disease, he said.
Amphibians all over the world are being affected by diseases, especially the deadly chytrid fungus, which was found in American bullfrogs in Kent, until they were eradicated, said Mr Langton.
As for the Aesculapian snakes, which are named after Asclepius [sic], the Greek god of medicine, he said: "It's a fascinating story. They are iconic animals and were on Roman coins as a symbol of healing.
"People will take snakes the wrong way and they'll think, Oh God … but they're not venomous and they're lovely animals, actually, if you get a chance to sit and watch them.
"It's unreal that they're in the UK."
Foreign invaders: Our new residents
Originally found in the tropics from Africa to Vietnam, but increasing in Britain, especially in the London suburbs. Considered a serious agricultural pest in their home range; fears they may be a pest in Britain, and also displace native bird species from their nesting holes.
Chinese mitten crab
A large crab from Asia, named for the hair on its claws, firmly established in the Thames. A predator of other species, it also causes trouble by burrowing into river banks.
An Asian insect with a highly variable appearance – it can have from 0 to 21 spots – it was first found here in 2004 and is now rapidly spreading across Britain. Preys on other ladybirds and could endanger some British species.
A fierce predator originally brought here for the fur trade, now found throughout the country. It fills an empty niche in Britain – a carnivore that can swim – and has nearly wiped out our native water vole in many areas.
A small fish originally from Asia that was brought here as an ornamental species and has now escaped into a number of water bodies in England. Likely to deplete native fish populations from competition and predation of eggs and fry.
A small deer from China brought in to deer parks has now spread across southern Britain in large numbers. Now causing damage to woodlands by eating out the undergrowth, leading to disappearance of woodland birds.