Scientists have issued a warning on 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 traumatising.
False widows are considered to be 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 bout of purple screaming,” Sarah Jane Dennehy told the BBC after her son was bitten.
“I stripped off his trousers and his lower 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 stripped off his top and a noble false widow spider crawled out from behind his ear.”
It took about 11 hours for the effects of the venom to wear off, she said.
Recent findings have suggested noble false widow spiders are up to 230 times more poisonous than native species in Irish homes.
Scientists found not only is the venom much more potent than that of any common northern European spiders, the species is also able to adapt its attacking behaviour to prevail in different scenarios.
They can make calculated decisions on whether to attack large or small prey depending on how much venom is left in their glands. If little venom is available, they avoid large opponents that could injure them, and instead focus on small prey, according to the study by a team of National University of Ireland, Galway researchers.
Co-author Dr John Dunbar said: “The tiniest amounts of venom - about 1,000th of a raindrop - can cause medically significant symptoms in humans that are about 250,000 times larger than them.”
Ms Dennelly said she had been in touch with the researchers following her son’s bite. “I want people to be aware that there are venomous 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 a bid to understand why it is so successful at spreading in towns and cities throughout the world.
Originating from Madeira and the Canary Islands, the noble false widow spider has the potential to become one of the world’s most invasive species of spider.
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 the London four years ago.
Additional reporting by Press Association
