A Snodland couple were shocked when they opened their door late at night to find a crab apparently trying to get in.

When Jane Byrne heard a noise she presumed it was hailstones – but was amazed to discover a blueish-grey crustacean scratching at the entrance to their May Street house at around 10pm yesterday.

Peter Byrne, 63, said: "We were watching the news. My wife thought it was hailstones, she opened the door and looked and then shrieked 'It's a crab trying to get in the door', so I grabbed the fly swatter."

The 3.5 inch-wide crab had put one claw across the threshold, as if to try and get into their home, the couple say.

"You see on TV when they put a foot in the door to stop it being shut, that's almost what it was like," Mr Byrne added.

However, when they switched the light on, the crab scuttled away immediately into a hedge.

"It was quite a big crab. I have no idea where they're coming from. It's very bizarre," he said.

Some five crabs have been spotted in the street in the past two weeks, he's been told, including one which had been run over.

Mr Byrne, who is a Scout leader, believes it may have been a Chinese mitten crab.

Mitten crabs have distinctive claws that appear furry, and he says his night-time visitor had similar features.

According to the Natural History Museum, Chinese mitten crabs are one of the world's 100 worst invasive species.

They cause problems by damaging river banks, modifying natural habitats and competing with native species.

Christian Castle works night shifts at the Smurfit Kappa paper mill, in Townsend, about a one-minute drive from the Byrne's street.

The site is opposite the River Medway and Mr Castle says he regularly sees crabs around this time of year near the warehouse and docking station.

There are more this year than usual, however, and he spotted about 30 on Saturday night, including one the size of his boot.

It is not known whether they were Chinese mitten crabs.

A resident at the nearby Holborough Lakes development also spotted a crab, about 10cm wide, next to his doorway at the weekend.

He lives very close to the lake and believes it may have come from there.

He hasn't seen it since, but believes it has been digging up shingle next to his house.

The father seems unphased by the crab, adding he and his wife had moved from London to be closer to nature.

Chinese mitten crabs can grow to the size of a dinner plate and the full extent of their distribution in the UK is unknown.

The Natural History Museum is asking the public to help by reporting their sightings.

It is not known for certain whether the crab spotted by the Byrne's was a Chinese mitten, but one thing is for sure: "We are not opening our door tonight," Peter said.

To report a sighting of a Chinese mitten crab, click here.

Escaped animals, unusual finds and news from the RSPCA can all be found here.

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