The common house spider may be more dangerous to humans than we think as people report "skin-eating" conditions following a bite.
A study has shown common house spiders can infect humans with harmful bacteria, while false widow spiders, which are found in Ireland, carry harmful strains that are resistant to common anti- biotics.
Although it is known that Australian black widows and funnel web spiders can be very dangerous with their potentially deadly venom, there has been until now little knowledge on just how harmful the common spider can be.
People across the world have reported rare "skin-eating" conditions after being bitten by a seemingly harmless European or North American spider.
It was previously believed the irritation was the result of infections caused by the victim scratching and probing the bite site with contaminated fingers.
However, a study by NUI Galway, which is published in the journal Scientific Reports, has confirmed that spiders carry harmful bacteria and that those germs can be transmitted to a human when the arachnid uses its fangs to bite.
The study was conducted by a team of zoologists and microbiologists.
Dr John Dunbar, a zoologist at the Ryan Institute's venom laboratory in NUI Galway, said there are 10 species of spider in north-western Europe that have fangs strong enough to pierce human skin and deliver venom.
The false widow is the only one considered of medical importance.
Dr Dunbar said that although urgent medical attention may not be needed for some bites, others can cause lasting infections that may lead to a hospital stay.
"Most of the time, a spider bite results in some redness and pain," he said.
"In some cases, however, victims seem to develop long- lasting infections for which strong antibiotic treatment - and sometimes a hospital stay - are necessary."
Dr Dunbar added that Ireland has seen an increase in bites, which in some cases proved difficult to treat with antibiotics.
Dr Aoife Boyd, also from NUI Galway and a senior author of the study, said the "diversity of microbes never ceases to amaze me".
She added that the power of microbes to "survive and thrive in every environment" is clearly demonstrated here as antimicrobial-resistant bacteria are even found in spider venom.