Analysis: meet the spider who can live for up to five years, produce 1,000 babies annually and whose bite can land you in hospital

By John P. Dunbar, Aiste Vitkauskaite, Sean Rayner and Michel M. Dugon, NUI Galway

The Noble false widow spider (Steatoda nobilis) has become a familiar sight in and around Irish homes in the past decade. Tabloids in Ireland and Britain regularly publish gruesome pictures of gaping wounds attributed to the supposedly devastating effects of its venom. But how accurate are those reports and what do we actually know about this spider?

At the NUI Galway Venom Systems Lab, we have been studying this spider for the past five years and we are finally learning the truth about the false widow story. The name "false widow" refers to its appearance, strikingly similar to "true" black widows and their characteristically dark, shiny, bulbous abdomen. As false widows often share the same habitats as black widows, it can be difficult to tell them apart. The relationship goes beyond their looks; they are, in fact, very closely related.

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But while the true black widow has a notorious (often exaggerated) reputation for being deadly, does the Noble false widow spider deserve to be Ireland's and Britain's public enemy number one? Many of us were first introduced to this spider through media headlines and articles describing it as purposely and viciously attacking people in their homes and delivering bites containing flesh eating venom and deadly bacteria.

The species is not a newcomer in Britain and the Noble false widow had already been reported in southern England near Torquay, Devon by the time Britain was gripped in the first Anglo-Boer War of 1880. However, the first bite officially recorded in the medical literature occurred more than a century later in 1991. Despite this initial medical report, the Noble false widow received little attention from the scientific community. From the 2000s onward, the species regularly headlined the media. This led us to begin a scientific investigation to try and establish fact from fiction.

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From RTÉ Radio 1's Morning Ireland, Dr Michel Dugon discusses a new survey about the Noble False Widow Spider

Our initial aim was to "debunk" alarmist media reports, but the Noble false widow spider turned out to be quite the surprise. Some 23 years after being first spotted in Ireland, the Noble false widow is now established in almost every county on the island. In east coastal counties such as Dublin, they are one of the most common urban spiders. One could catch 150 adult spiders, in just a few hours, and return to the same location a few weeks later to find equally large numbers.

From an ecological standpoint, spiders are keystone organisms, fundamental to their ecosystems. Globally, they consume 400 to 800 million tons of arthropods annually, which include agricultural and medically important pests. Each species plays a specific role within the ecosystem, often specialising in a handful of prey types. Ireland has one of the poorest spider species diversity in Europe with less than 400 species compared to over 600 in Britain and over 1.600 species in France.

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The Noble false widow has a list of traits that make it competitive against native Irish spiders. Cold tolerant and active all year round, it has a five-year lifespan, produces 1,000 babies annually and subdues a diverse range of prey including spiders, bees and even native lizards. In contrast, most of our native spiders are inactive during the coldest months, have shorter lifespans and produce fewer offspring.

Drop for drop, the venom of the Noble false widow is far more potent than any of the native spiders we have assessed and has superior prey capture and predator avoidance strategies. All our observations show that the Noble false widow takes over habitats and displaces native species. In the long term, this can have catastrophic consequences: further loss of diversity due to displacement by the Noble false widow could have a detrimental impact on Irish ecosystems.

What's for lunch? A Noble false widow spider tucks into a wasp. Photo: NUI Galway Venom Systems Lab

There are currently 49,434 species of spiders known worldwide. Virtually all of them are venomous, including our native spiders and, of course, the Noble false widow. However, spiders have evolved venoms to target biochemical pathways of different prey and therefore, some are more toxic to humans.

We discovered that the Noble false widow shares two-thirds of its venom toxins with the true black widow, including powerful neurotoxins that affect the nervous system of mammals, including humans. It turns out that the venom can pack quite a punch. The number one symptom is mild to debilitating pain and swelling. Some victims experienced tremors, reduced or elevated blood pressure, nausea, and impaired mobility, which closely resemble symptoms caused by the venom of true black widows. In rare instances, victims developed minor necrosis while others were treated for severe bacterial infections. Our research confirms that the Noble false widow does carry harmful bacteria on their fangs that can be resistant to antibiotics.

Our research confirms that the Noble false widow does carry harmful bacteria on their fangs that can be resistant to antibiotics

But before running for the hills, we must realise that spiders do not bite randomly. Venom is a complex and precious resource for any animal: it requires lots of energy and several weeks to produce. It is a precision tool that requires careful metering when administered. Using too little of it would render the attack inefficient, and the spider may end up injured or killed. Using too much could leave the spider venomless and vulnerable for days or weeks.

Spiders have evolved the amazing ability to make very quick informed "decisions" as to when and how much venom to inject. With this in mind, we can rest assured that it does not go about its daily business wanting to inflict bites on us humans; it would much rather hide and save its precious venom for tasty bugs.

The team's full study on the Noble false widow spider can be read here

Dr John Dunbar is a Postdoctoral researcher at NUI Galway who completed his doctoral research on the ecology, venom and potential medical importance of the Noble false widow spider. Aiste Vitkauskaite is a MSc student in Toxicology at NUI Galway. Sean Rayner is a Zoology and Earth and Ocean Sciences graduate from NUI Galway, currently completing a MSc in Toxicology. Dr Michel Dugon is a lecturer in Zoology and Principal Investigator of the Venom Systems Lab at NUI Galway. He is a former Irish Research Council awardee.


The views expressed here are those of the author and do not represent or reflect the views of RTÉ