Scientists have issued a warning about noble false widow spiders after a 15-week-old baby was bitten by one and taken to A&E in Ireland.
A mother said her son Charlie fell ill and had to be taken to hospital in an incident she described as traumatic.
False widow spiders are considered the most venomous type of spider in the UK.
“Charlie was lying on his mat and all of a sudden he went apocalyptic – he had a real fit of purple screaming,” Sarah Jane Dennehy told the BBC after her son was bitten.
“I took his pants off and his left leg was swollen, it was bright red and there were three bites.”
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The mother, from County Cork, added: ‘Then I took her top off and a noble false widow spider crawled behind her ear.’
It took about 11 hours for the effects of the venom to wear off, she said.
Recent findings have suggested that noble false widow spiders are up to 230 times more poisonous than native species in Irish homes.
Scientists have found that not only is the venom much more potent than that of any common northern European spider, but the species is also able to adapt its attack behavior to prevail in different scenarios.
They can make calculated decisions on whether to attack large or small prey based on the amount of venom remaining in their glands. If little venom is available, they avoid large opponents that could hurt them and focus instead on small prey, according to a study by a team of researchers from the National University of Ireland in Galway.
Co-author Dr John Dunbar said: “The smallest amounts of venom – about 1,000th of a raindrop – can cause medically significant symptoms in humans that are about 250,000 times greater than ‘them.”
Ms Dennelly said she had been in contact with researchers after her son was bitten. “I want people to know that there are poisonous spiders in Ireland and the UK,” she told the BBC.
The study – published in the journal Toxins – investigated the potency of the false widow spider’s venom in an effort to find out why it’s been so successful in spreading to cities around the world.
Native to Madeira and the Canary Islands, the noble false widow spider has the potential to become one of the most invasive spider species in the world.
It was first reported in southern England in 1879 and has since spread to the rest of the UK.
Schools have even been closed after false widow spiders were detected or suspected on site – including a number in London four years ago.
Additional reporting by Press Association