Microhabitat use and artificial-light related occurrence of the brown widow spider Latrodectus geometricus in a newly invaded area of the inland Kanto region, Japan

[Abstract] : The invasion of the brown widow spider into Japan was first recorded in 1995. Since then, its establishment has been recognized mainly in major port areas, but further invasions are recently found from inland areas in the Kanto region of Japan. We thus attempted to clarify the actual status of its invasion by conducting a pilot extermination in a suspected area between October 13, 2022 and January 20, 2023. A total of two males, 39 females, and 83 egg sacs were recovered from 46 nests during our extermination. The nesting sites were typically found on or inside inconspicuous part of artificial outdoor objects, especially behind plastic benches and in recesses on the outer walls of buildings. These microhabitat uses were concentrated in environments where the surroundings were lit up by street and building lights at night. Artificial lights have a function to attract phototaxis insects so that the distribution of nesting sites is likely to be affected by the availability of these potential food sources. As this species has the potential to expand its distribution far inland more, additional surveys are required to predict future invasions and ecological impact.