Warnings over noble false widow spider bites as numbers surge

Scientists have discovered that bites from noble false widow spiders can be so severe that they require hospital treatment, amid a sudden surge in their numbers in the UK and Ireland.

Spider experts and healthcare specialists have debated the threat posed by the noble false widow for many years.

A new study, published in the international medical journal Clinical Toxicology, has now confirmed that some bite victims experience symptoms similar to the true black widow spiders, with some severe cases requiring hospital admission.

Originating from Madeira and the Canary Islands, the noble false widow spider Steatoda nobilis now has the potential to become one of the world’s most invasive species. It was first documented in Britain over 140 years ago, but in recent decades the species has suddenly increased in numbers, significantly expanding its range and density.

The reasons behind this sudden expansion are not clear.

Scientists have ruled out climate change as the likely cause but have suggested that a new genetic mutation may have made them more adaptable to new environments.

They also appear to have benefitted from an ever-increasing globalised economy, hitchhiking in containers and crates throughout the globe.

Human movement has largely contributed to spread this species throughout Europe, North Africa, West Asia and parts of North and South America.

In parts of Britain and Ireland, it has become one of the most common species of spiders found in and around urban habitats.

With the increase in false widow spiders around homes, bites are becoming more prevalent, and scientists are now beginning to realise the full medical significance of these spiders.

Symptoms of envenomation – the process by which venom is injected by the bite – can be both localised and systemic, ranging from mild to debilitating pain and mild to intense swelling.

Some victims have experienced tremors, reduced or elevated blood pressure, nausea and impaired mobility.

In rare instances, victims have developed minor wounds at the bite site or had to be treated for severe bacterial infections.

A team of scientists from NUI Galway established a DNA database to allow clinicians dealing with cases to confirm the species identity using genetic analysis.

Dr Michel Dugon, head of the venom systems lab at NUI Galway and senior author of the study, said: ‘In addition to their medically significant venom, noble false widows are extremely adaptable and competitive in the wild.

‘Two decades ago, this species was almost unknown in Ireland, the UK or in continental Europe.

‘We still have much to learn about its genetics, origin, behaviour and development. One thing is certain though, this species is here to stay, and we must learn how to live with it.’

Dr John Dunbar, postdoctoral researcher at the lab at NUI Galway and lead author of the study, said: ‘We are encouraging people to capture a photograph of the spider immediately after being bitten.

‘Our latest study confirms without a doubt that noble false widows can cause severe envenomations.

‘This species is increasing its range and population density which will undoubtedly lead to an increase in bites.

‘While most cases will have a mild outcome, we need to continue to closely monitor bites by the noble false widow to understand the potential range of symptoms and to treat severe cases when they occur.’