Ireland’s deadliest spider even more dangerous than believed

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False widow spider

Spider bites are quite rare. But researchers at NUI Galway have found that common house spiders and false widow spiders are perhaps more dangerous than people think.

In a study published today, NUI Galway researchers found that common house spiders carry harmful germs which can cause infections in humans when they use their fangs to bite.

More worryingly, they found that the infamous false widow spider carries harmful bacteria which are resistant to common antibiotic treatments.

People bitten by spiders in recent years have suffered from a range of symptoms. Rare ‘skin eating conditions’ after spider bites were thought to be secondary infections, caused by people scratching the skin where they were bitten.

But the new research, published in the international journal Scientific Reports, confirms a theory which has been debated for years – and explains these strange infections.

Many spiders have been shown to have venom with antibacterial activity, and it is often debated as to whether the venom would neutralise bacteria.

But the research shows that at least for the false widow spider, which is native to the Canary Islands, the venom does not inhibit bacteria.

“The diversity of microbes never ceases to amaze me,” said Dr Aoife Boyd, Director of the Pathogenic Mechanisms Group at NUI Galway’s School of Natural Sciences, and senior author of the study.

“The power to survive and thrive in every environment is shown here by the presence of antimicrobial resistance bacteria even in spider venom.

“Antimicrobial resistance (AMR) is an urgent and growing problem worldwide. A One Health approach interconnecting human, animal and environmental health is the only way to tackle the problem.”

Dr John Dunbar, Zoologist at the Ryan Institute’s Venom System Lab in NUI Galway, said that about ten species of spiders common in North-western Europe have fangs strong enough to pierce human skin and deliver venom, but only one of them – the recent invasive noble false widow spider – is considered of medical importance.

“Most of the time, a spider bite results in some redness and pain.

“In some cases, however, victims seem to develop long lasting infections for which strong antibiotic treatment – and sometimes a hospital stay – are necessary.

“It is this increasing range expansion and massive rise in dense populations of false widow spiders around urbanised areas across Ireland and Britain that has seen a rise in bites with some severe envenomation symptoms but also infections, which in some cases proved even difficult to treat with antibiotics,” said Dr John Dunbar.

Neyaz Kahn, co-lead author of the study and PhD student at the Pathogenic Mechanisms Group in NUI Galway’s School of Natural Sciences, added that the study shows that spiders are not just venomous but are also carriers of dangerous bacteria capable of producing severe infections.

“The biggest threat is that some of these bacteria are multi-drug resistant, making them particularly difficult to treat with regular medicine.

“This is something that health care professionals should consider from now on.”