# Survey of Synanthropic Spiders in Ireland Reveals Expansion and Dominance of the Invasive Noble False Widow Steatoda nobilis in Urban Habitats (Araneae: Theridiidae)

## TL;DR

This study finds that the invasive Noble false widow spider is becoming dominant in urban areas of Ireland, outcompeting native species.

## Contribution

The first comprehensive survey of synanthropic spider populations in Ireland, revealing the expansion of Steatoda nobilis into new regions.

## Key findings

- Steatoda nobilis and Zygiella x-notata together make up over 80% of spider abundance in surveyed urban areas.
- S. nobilis is now established in two new Irish counties, Co. Mayo and Co. Sligo.
- Synanthropic spider diversity is influenced by seasonality and prey availability, but not daily weather.

## Abstract

Rapid urbanisation has led several spider species to adapt to synanthropic microhabitats and establish large populations outside of their native ranges. In Ireland, the establishment and widespread distribution of the Noble false widow spider
Steatoda nobilis
(Araneae: Theridiidae) (Thorell, 1875) has raised questions about its impact on native spider populations across the country. Through an extensive field survey of six urban centres over an 11‐month period, we sought to establish population demographics for
S. nobilis
and other synanthropic spiders in Ireland for the first time. We surveyed fence microhabitats for both spider abundance and diversity to determine the influence of variables such as prey availability and climate. Of the 20 identifiable species observed,
S. nobilis
and the missing sector orb weaver
Zygiella x‐notata
(Clerck, 1757) typically made up more than 80% of the spider abundance regardless of location surveyed, including two new Irish counties where
S. nobilis
had previously not been recorded but is now well established (Co. Mayo and Co. Sligo). Our results also indicated that the diversity of synanthropic spiders is significantly affected by seasonality and prey availability, but largely unaffected by daily weather conditions.

Rapid urbanisation has facilitated the establishment of large populations of the Noble false widow spider outside of its native range through the use of synanthropic microhabitats. In Ireland, we survey these favourable microhabitats for spider diversity for the first time and find that the Noble false widow now typically makes up more than 40% of the assemblage.