Intraguild impact of the invasive  Noble false widow spider  Steatoda nobilis (Thorell, 1875) in Ireland

With rapid urbanisation during the Anthropocene, several generalist spider species have adapted to synanthropic microhabitats and have established large populations outside of their native ranges. On the island of Ireland, the establishment and distribution of the Noble false widow spider Steatoda nobilis (Araneae: Theridiidae) (Thorell, 1875) within the last 20 years has spurred questions relating to its effect on native spider populations, the likelihood of other Theridiid spider establishing on the island, such as the medically significant black widows of the genus Latrodectus, and the likelihood of S. nobilis to establish in highly endemic insular habitats. Through an extensive field survey of six urban centres, we seek to establish population demographics for Steatoda nobilis and other synanthropic spiders in Ireland for the first time. We survey fence/railing microhabitats for spider density and diversity over the course of 11 months to draw comparisons with other variables such as prey availability and climate. In total, 20 identifiable spider species were observed occupying fence/railing microhabitats in urban centres around the island. Results indicate that S. nobilis and the missing sector orb weaver Zygiella x-notata (Clerck, 1757) typically make up more than 80% of the spider abundance within favourable microhabitats in Ireland regardless of the location surveyed; this includes two new counties where S. nobilis was previously not recorded but is now well established (Co. Mayo and Co. Sligo). The results also indicate that the diversity of synanthropic spiders is significantly affected by prey availability but not by daily weather conditions nor the removal of spiders through non-pesticidal means. Additionally, a comprehensive literature review of previous Latrodectus introductions to Ireland was conducted to determine the likelihood of establishment on the island. In addition to three published records, three additional records of Latrodectus importation, including the first record of L. hesperus in Ireland, were compiled and analysed. The global fruit trade was identified as a primary vector for black widows entering Ireland. Analysis of the case history indicates that it is unlikely that any member of the genus Latrodectus will be able to establish large populations on the island without relying on specific human-made structures (i.e., hot-houses). Overall, the data indicates that Steatoda nobilis’ rapid dispersal, large populations in urban microhabitats, and ability to outcompete native species in a lab setting meet the criteria to be considered an invasive species in Ireland. More synanthropic diversity surveys and comparative studies will be needed to understand the traits that make S. nobilis an effective alien species on a global scale, and to prevent it from invading areas of high endemism.

Publisher

NUI Galway

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Attribution-NonCommercial-NoDerivs 3.0 Ireland
CC BY-NC-ND 3.0 IE

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Collections

University of Galway Theses (Research Masters Theses)