This photo of a weasel riding on the back of a woodpecker has gone viral after it was posted on social media.

It has been picked up by media outlets worldwide. Speaking to BBC News, the photographer Martin Le-May said he was "taken aback" by how many people were sharing the photo.

The weasel was not using the woodpecker for transport, but was actually after a tasty meal.

BBC Earth now has a challenge for you: can you top this photo?

Today, we are launching BBC Earth Capture, a series of video and photo challenges.

Each will have a separate theme, for you to interpret how you wish.

In honour of the weasel and woodpecker, our inaugural challenge is called Extraordinary.

If you've captured something extraordinary in nature share it with us, and we'll share it with the world.

Find out how to take part by clicking this link: Take the BBC Earth Capture challenge.

Or, if you'd prefer, tweet us with your pictures.

So how did this picture happen?

It was an unusual sight to encounter on a stroll on a dull day in March.

A strangled, distressed squawking and a flash of green grabbed the attention of Martin Le-May and his wife Ann as they walked around Hornchurch Country Park, Greater London in the UK.

Hiding behind a tree with binoculars to get a better view, the pair was stunned to witness a ferocious tussle between a green woodpecker and a weasel.

And then something amazing happened: the woodpecker took flight with the weasel clinging onto its back.

The photographs capturing the moment are extraordinary. They’ve been shared thousands of times on social media and have been picked up by a plethora of news outlets. But how extraordinary was the event itself, and what exactly was going on?

Unlike many other woodpeckers, [green woodpeckers] spend a lot of time feeding on the ground on ants around ants’ nests... The weasel will hang around and wait for an opportunity to eat sort of anything that they can

“I’ve never seen anything like it,” says Dr Stuart Marsden, reader in Conservation Ecology at Manchester Metropolitan University in the UK, who has studied green woodpeckers extensively.

Weasels are ferocious predators that usually predate mammals – they can take on animals bigger than themselves and often eat rabbits. But it’s more unusual for them to attack birds.

“I wouldn’t think that woodpeckers are often taken,” says Dr Marsden. But woodpeckers are ground birds. Weasels go after their eggs and babies, and sometimes adults that are trying to defend the nest.

He thinks the woodpecker was probably feeding in the grass when it was ambushed. The birds’ diet is mainly ants.

“Unlike many other woodpeckers, they spend a lot of time feeding on the ground on ants around ants’ nests."

“The weasel will hang around and wait for an opportunity to eat sort of anything that they can eat.

“They are really vicious and clever,” he adds.

“Unfortunately it’s gripped on here and it’s been taken for a ride.”

Naturalist and broadcaster Iolo Williams told the BBC: “These are truly amazing photographs. It’s worth remembering that weasels have a truly catholic diet – I’ve seen them taking fully grown rabbits.

“They are incredible predators, so I don’t think it’s that remarkable that one tried to take a woodpecker.

“What is remarkable was that it was captured on camera.”

Weasel vs woodpecker

Green woodpeckers grow to around 32cm (12.5in) in length while male weasels measure around 20-22cm (7.9-8.6in) and females reach 15-18cm (5.9-7in)

In weight, green woodpeckers vary from 180 to 220g (5.6-7.8oz), while adult weasels usually weigh between 106-131g (3.7-4.6oz) for males and 55-69g (1.9-2.4oz) for females.

Dr Marsden told BBC Earth: “For a bird like that to take off from the ground, to lift itself off the ground with a heavy [load] on its back is quite impressive really.”