Exotic species of spiders are making their homes in the UK, scientists say.
Researchers believe arachnids arriving in imports of food and plants are now able to survive and spread thanks to the UK's increasingly mild climate.
The new inhabitants include a species of false widow spider and some believe the deadly black widow could be next to invade.
Conservation group Buglife wants import rules to be strengthened to stem the tide of alien species invasion.
Matt Shardlow, director of Buglife, told BBC News: "Other countries in the world take great care about what biological material they allow in, because it can contain pests that can damage our goods, our livelihoods, our health and our biodiversity.
Our increasingly warm climate is starting to suit many more spiders
"Currently in the UK, we have a laissez-faire attitude - there is an open licence for people to bring in dangerous pests."
But a spokesperson for the Department for Environment, Food and Rural Affairs (Defra) said that a new strategy was in place to "tackle the threat to the UK's native biodiversity from unwanted pest species which have 'hitchhiked' into the UK on plants".
All this week, BBC News will be taking a closer look at some of the alien invaders that are in the UK.
John Partridge from the British Arachnological Society said his organisation had had an increase in the number of enquiries about "strange spiders".
He added: "We are certainly getting more spiders coming into the UK - and it seems that more are spreading around the country once they are in."
False widow Steatoda paykulliana is a new resident in the UK
One new inhabitant is Steatoda paykulliana, a false widow spider that is native to Southern Europe, West Asia and North Africa.
It is about 0.7-1.5cm (0.3-0.6in) in size and can bite.
While this spider had been spotted in the UK in the past, it was thought that no colonies had established.
But Stuart Hine, who runs the Insect Identification Service at the Natural History Museum, said this was no longer the case.
He said: "Now we have found it in Plymouth. And it looks as if it is here to stay."
The arrival of exotic spiders and insects that had hitched a ride on various imports was not a new phenomenon, said Mr Hine.
"If there was a warm period they would be able to survive, but a cold snap would kill them off," he explained.
"But now, our increasingly warm climate is starting to suit many more spiders - and once they come in, they are able to stay put."
This has also meant that some invasive species that once only existed within a few small pockets in the UK have been able to spread.
Steatoda nobilis is one such spider.
UK's 'most venomous' spider
This false widow is thought to have first arrived in the UK from the Mediterranean in the late 1800s.
For many decades it remained in a small area within Devon, but about 15 years ago it began to spread and it can now be spotted all along the South Coast.
In spider terms, it has to be said that [the tube web] is an aggressive spider
Stuart Hine, NHM
Mr Hine said: "It has a nasty bite - and some people can have a bad reaction to it."
The tube web spider (Segestria florentina), another non-native biting spider, has also been on the move, spreading from the South Coast much further north.
It is a large spider, measuring between 1.5cm and 2.2cm (0.6-0.9in), with green iridescence on its jaws.
Mr Hine said: "In spider terms, it has to be said that this is an aggressive spider.
"If you approach it, it raises its legs and bares its fangs.
"Most spiders will back away - this one will jump at you and bite."
Mr Hine believes that the black widow spider could be next on the list for the UK.
He said: "There is no great reason that they wouldn't survive here now - winters are now mild enough.
"It really is only a matter of time."
A bite from this highly venomous spider is extremely painful, and in a small number of cases can be fatal.
A balancing act
While experts stress that not all new species have a negative impact, they do warn that trade is a key factor in the number of new species that enter the country.
Defra is responsible for checking the products that enter the UK.
Could the deadly black widow be our next alien invader?
A spokesperson told the BBC: "The government and its agencies work with businesses, overseas authorities and the general public to minimise the risk of exotic animal and plant pests and diseases from entering the country and threatening public health, livestock, agriculture, horticulture and the environment.
"Disease can enter the country in many ways; that's why Defra undertakes international disease monitoring, while there are also strict controls on the movement of livestock and animals."
But Mr Shardlow from Buglife said: "We cannot just view moving biological material around like other trade products.
"You have to have a bit of environmental awareness, and I think we should be looking to import and export less biological material."
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