Nationwide survey shows invasive spider thriving in urban centres

The invasive Noble false widow spider (Steatoda nobilis) is now one of the most common urban spiders in Ireland, according to a new study by researchers at the University of Galway.

Researchers surveyed urban spider populations across the Republic of Ireland to identify the most common species and the environmental factors influencing their diversity and abundance.

The study found that the Noble false widow and the long-established missing sector orb weaver (Zygiella x-notata) accounted for more than 80% of urban spider populations. Remarkably, the Noble false widow is now well established even in counties such as Mayo and Sligo, where it was previously unrecorded.

The findings, been published in Ecology and Evolution, highlight Ireland’s understudied urban habitats, as well as the potential negative impact of the Noble false widow on native spider species

            Brandon Collier, doctoral researcher at University of Galway and first author of the study, said: “This research provides a framework for studying a largely overlooked habitat for invasive and medically important species. As human populations increase year after year, urban areas grow with them. Understanding the impact this has on native species in Ireland provides essential knowledge for preventing and managing invasions in more fragile environments like Australia, New Zealand, and Japan.”

Rapid global trade has allowed more spider species to spread beyond their native ranges to become cosmopolitan and, occasionally, invasive. False widows and their relatives, the black widows, have led this trend, with implications for human and environmental health.

While the strong venom potency and medical importance of certain widow spiders is well documented, their ecological impact has been harder to determine.

To better understand urban spider populations, researchers developed a visual survey framework that could be applied internationally to monitor invasive species.

The scientists are calling for the Noble false widow spider to be officially recognised as an invasive species under the UN Convention on Biological Diversity’s guidelines because of its rapid spread and potential impact on native spiders.

The research was carried out by established and postgraduate scientists from the University of Galway, with funding through the University’s Hardiman Scholarship held by Brandon Collier.

            Mr Collier added: “Now more than ever, we need to evaluate the threat of potentially invasive spider species and formulate a global action plan to prevent negative impacts on sensitive native species. Collaborating with international research groups has allowed us to begin the dialogue, but implementing policy changes in affected regions is essential to preventing future wide-spread invasions.”

                Dr Michel Dugon, Head of the Venom Systems Lab at University of Galway and senior author of the study, said: “The populations of Noble false widows have exploded throughout Western Europe in the past two decades, and the species has been recently observed in New Zealand, South America, the US, and North Africa. Our next step is to understand the physiological adaptations of the species to better predict other areas at risk of invasion.”

            Dayle Leonard, doctoral researcher at University of Galway and co-author of the study, said: “This research highlights a threat to biodiversity that is largely ignored. We were able to show how though Irish weather varies greatly, spider diversity is more affected by the seasons, food, and, potentially, the presence of the invasive Noble false widow spider. There are global implications with the spread of the Noble false widow across continents, so providing insight into its dominance and its impact in urban environments is vital.”

The full study in Ecology and Evolution is available at https://doi.org/10.1002/ece3.73193.

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