An insect that normally inhabits warm countries has been found living and breeding in the UK, entomologists say.
Experts say its arrival in the UK is a clear sign of climate change
The green "shield" bug, which attacks a broad range of crops, is usually seen in the Mediterranean, Middle East, Australia, North America and Africa.
Its arrival in Britain is a clear sign of climate change, claim experts from the Natural History Museum, London.
"I'm always reluctant to invoke global warming but it's the only explanation," said curator of beetles, Max Barclay.
The green vegetable bug (Nezara viridula) is similar to the UK's native green shield bug (Palomena prasina), but is paler in colour and has a longer, narrower shape. Also, unlike its British cousin, the green vegetable bug has no brown markings.
The insects - sometimes known as "stink" bugs, because of the foul odour they emit when threatened - are regular stowaways to the UK.
They often get shipped in with imported vegetables but, until recently, they have not been able to stand Britain's cold climate.
Now three healthy colonies have been found in London - two in the Queen's Park area and one in Kings Cross.
"When somebody first brought a specimen to me I didn't believe it," Dr Barclay told BBC News Online. "I thought somebody had picked it up on their holidays, but it really was eating their tomatoes in London."
Of course, if three colonies have been found, the actual number is likely to be far higher.
"It is not something that is going to attract much attention," said Dr Barclay. "So there may well be several colonies living unnoticed."
This is not the first time an insect that usually likes warm weather has come to the UK. But the really interesting thing about the green vegetable bug is that we know it could not survive here in the past.
"World experts on this group said in 1959 that it can't establish in the British Isles," said Dr Barclay. "They said it is a regular import - it is always coming in - but it can't live here.
"And for 40 years there was no record of it, so they seemed to be correct. But obviously something has changed now."
The "urban heat island effect" is one possible reason why London is now an acceptable temperature for green vegetable bugs.
It is a well known phenomenon that big cities such as London are a couple of degrees warmer than the surrounding countryside. The asphalt and concrete for roads, buildings, and other structures absorb the Sun's heat, causing surface temperatures and overall ambient temperatures to rise.
But is this effect sufficient to make London a suitable home for stink bugs? Experts at the Met Office suspect not.
"Both global warming and the urban heat island effect are going on," Dr Richard Betts, from the Met Office, told BBC News Online. "But I would say the global warming effect is probably the largest.
"I wouldn't have thought the urban heat island effect would have been so overwhelming in the last 20 years."
Dr Barclay added: "I don't think [the urban heat island effect] has caused it to be warmer here than it was in the 60s or 70s."
He continued: "I have been looking at a lot of new species that have come in over the years - but this is the only one that tells a clear story about global warming.
"In all the other cases people say, 'Is this to do with global warming?' And we have to say we are not sure. But in this case, we are sure."