A Question of Nature: How hidden is the UK's wild side?
London's little known wildlife is revealed by a new BBC programme. Does the UK have a secret wild side, and what little known creatures lurk hidden within our shores?
Scorpions, parakeets, terrapins, alligator snapping turtles, and tree frogs all live in the wild... in Britain.
As strange as it may sound, the UK has become home to a wide variety of animals and plants from around the world.
But it is not just exotic animals living secret wild lives... some of our native British wildlife can be found doing surprising things to ensure their survival.
The BBC Two programme Natural World: Unnatural History of London, shows pigeons using the Tube to get around the city, a seal that takes fish from fishmongers outside Billingsgate Fish Market, and foxes that will "sit" if given sausages.
And you have been in touch with BBC Nature, telling us that strange and wonderful things can be seen in Britain.
While some of the animals spotted have been released either deliberately or by accident, others have arrived by themselves like the great white egrets that recently bred for the first time in the UK.
Two of the UK's 24 bumblebee species have disappeared from our shores in the last century and another six are seriously threatened, yet one non-native species, the tree bumblebee (Bombus hypnorum), is quickly spreading.Bees in boxes
It only arrived from Europe about a decade ago and appears to have naturally spread rather than having been released.
Unlike our mainly ground-nesting species, these bumblebees nest in trees, although they are also making use of the nestboxes intended for birds many people have put up.
Sally Huggett tweeted: "We have tree bumble bees nesting in our bird box in East Sussex," and Ian Bailey from north-east Hampshire also tweeted saying that he believes he has "tree bumble bees in a nest box".
The fact that France is so close and the habitat so similar, the biggest question many experts have is why it took so long for tree bumblebees to arrive.
"This month I saw an otter swimming up the River Dee in Aberdeen city at 10 o'clock in the morning," tweeted Anne Williamson.
From Aberdeen to Andover, many of you got in touch with BBC Nature telling us you have recently seen urban otters.
A few decades ago, spotting an otter in an urban environment would have been a very rare occurrence due to polluted, sterile rivers and canals.
Otters are apex predators, mainly relying on catching fish so the fact they are now increasingly common means there are now fish back in our rivers.
Britain's secret wildlife
- Terrapins' natural home is the swamps of the US. See how the 1990s craze for pet terrapins resulted in many being dumped into lakes when they grew too big..
- Thirty years ago otter sightings were extremely rare, you can now see otters in our busiest cities thanks to the cleaner waterways.
- In 2010 an extremely rare alligator snapping turtle was caught in a West Midlands reservoir.
- Watch the theories of how exotic-looking ring-necked parakeets escaped from an aviary and taken to the British climate and suburbia.
- The UK has populations of the kangaroo-like red-necked wallaby in Scotland and Isle of Man with other sightings all over the UK.
- Natural England has confirmed sightings of raccoons and Siberian chipmunks in the UK and many unconfirmed sightings of big cats.
The fish the otters feed on in turn rely on smaller fish and invertebrates; our river ecosystems are much healthier.
Otters are now found in "most watercourses in Scotland... Dundee or Edinburgh would appear to be the best places to come and see them," said Greg Tinker from the Scottish Wildlife Trust.
But what most people have been telling us about is a bird that may seem more at home in sunnier climes.
The sight and sounds of a raucous flock of ring-necked parakeets are well known to Londoners but sightings elsewhere around England are on the up.
Ring-necked parakeets originate from sub-saharan Africa and Asia but were a favoured pet of the Romans and have been found throughout Europe far longer than in the UK.
Their stronghold is south-east England so we investigated reported sightings sent to BBC Nature from Studland in Dorset and Castleford in Yorkshire.
"They are everywhere... there is even a pair in St Andrews which is surprising because it's so cold up there," said Hannah Peck, who is conducting her Imperial College London PhD study: Project Parakeet.
Ms Peck has been investigating ring-necked parakeets in south-east England for nearly three years and estimates the population just in south-east England is around 32,000 but could be up to 50,000.
"People can record sightings [of parakeets] at BirdTrack which is part of the BTO."
But they are not the only animals to have found the UK surprisingly hospitable.
It was estimated at last count that 13,000 yellow-tailed scorpions, originally hailing from north-west Africa and southern Europe now live in the south-east, with several populations of at least 1000 around London, and large numbers on the Isle of Sheppey, Kent.
Dr Toni Bunnell, a biologist at the University of Hull, says the scorpions have also been "down at Sheerness docks and on the north Devon coast for about 120 years".
"They are thought to have come in on ships from Italy on stonework."
Craig Macadam, Scotland director with Buglife, says scorpions love masonry.
"They are associated with brick walls, which warm up in the sun down there in the south."
But a marching scorpion army is not about to advance across the country.
"Invasive species tend to spread along the south coast and then move north, but they've got a nice live colony and it's likely they are staying put," Dr Bunnell says.
Elsewhere, about 10 coatis, also known as Brazilian aardvarks, are living wild in Cumbria, 20 alligator snapping turtles, also from North America, are believed to be living wild in parts of Kent, London, the West Midlands and West Yorkshire.
One species of false black widow spiders, Steatoda nobilis crawled in to Devon about 100 years ago after arriving from the Canary and Madeiran Islands, and is slowly spreading.
Craig Macadam says invasive species can be found creeping across the UK - many heading to Scotland as temperatures get warmer.
"Two or three new species of dragonfly have been found in the UK in the last year and a half," he says.
"They are quite active fliers and can move around and respond to subtle changes in the weather."
The dainty damselfly, a dragonfly relative, is one such creature, whose reappearance after last being seen in the 50s amazed scientists.
But other invertebrates also have made the UK their home - like a snail so far only found in stately homes.
Sea life not normally seen in British waters could also be becoming more common.
Great white sharks could be "occasional vagrant visitors", according to Richard Peirce, chairman of the Shark Trust.
He says it is a real surprise that Britain does not have an established great white shark population, because the conditions in British waters mirror those they like elsewhere.
From the reports coming in to BBC Nature, some of the UK's secret wild side might not stay so secret in the future.
Native animals are developing new behaviours to survive and new species are setting up residence on our shores under their own steam.
And while many released alien species are not yet capable of establishing feral populations they, like the ring-necked parakeets, could become part of our landscape in the future.
So keep your eyes peeled next time you are out as you may catch a glimpse of wildlife you never knew was out there.
Natural World: Unnatural history of London is on BBC Two on Monday at 20:00 BST.