Occurrence, reproductive rate and identification of the non-native Noble false widow spider Steatoda nobilis (Thorell, 1875) in Ireland

The noble false widow Steatoda nobilis (Thorell, 1875) has established thriving populations in urban centres throughout England and Wales since it was accidentally imported from the Canary Islands and Madeira to Britain over a century ago. In recent years, Steatoda nobilis has colonised parts of Western Europe, California, Chile and the Middle East. In Ireland, Steatoda nobilis was first recorded in 1999 from a single location in Co Wicklow. The present study examines the current range and main habitats of Steatoda nobilis in Ireland and assesses its potential as an invasive species by documenting its reproductive rate. Additionally, we present photographic material illustrating the intraspecific phenotypic variations exhibited by Steatoda nobilis to assist in correct identification of this species by the public. Our data shows that Steatoda nobilis is an extremely prolific, resilient species with distinct synanthropic affinities. This species currently occurs in at least sixteen Irish counties with the largest populations observed in the greater Dublin area, where it has become widespread in buildings and on street furniture. Steatoda nobilis seems to be currently absent from natural, undisturbed habitats such as woodlands, bogs and grassland. We suggest that due to its comparatively fast reproductive rate, long life span and year-round activity, Steatoda nobilis might have a detrimental impact on native urban-dwelling spiders.