Web placement in grass spiders (Agelenopsis pennsylvanica) is driven more by artificial light at night than by prey
Web placement in grass spiders (Agelenopsis pennsylvanica) is driven more by artificial light at night than by prey
Light from human-modified landscapes (artificial light at night, or ALAN) can disrupt feeding, rest, reproduction and orientation in many animals. It is considered a contributor to global insect declines, and studies have found that up to one-third of insects attracted to stationary light sources die from exhaustion or predation by sunrise. Many insectivorous vertebrates hunt near artificial light to catch more prey, but few studies have examined whether invertebrate predators similarly exploit artificial light. Here we test how artificial light and prey affect web placement in the grass spider Agelenopsis pennsylvanica (Araneae, Agelenidae). We kept spiders in enclosures that had transparent sides, with a light source outside one corner. In the first experiment, lights either stayed on (light treatment) or off (control) all night, and we compared web placement between groups. Next, we conducted a cue conflict experiment, with light in one corner and prey in a separate unlit corner, and compared web placement between the light and control groups. In the absence of prey, control spider web placement was random while light treatment spiders were more likely to build webs in the lit corner and made their webs significantly closer to the light source. When prey was present, control treatment spiders were more likely to build webs near the prey, while light treatment spiders were still more likely to build webs in the light, and their webs were significantly closer to the light and farther from the prey compared to control spiders. Outdoors, this likely draws them to prey-dense, artificially lit areas. Recent reports, however, suggest that urban insects are evolving reduced flight-to-light behaviour. If spiders continue to prioritize light over prey, artificial light could therefore become an ecological trap for spiders if fewer insects approach the light. This work highlights the complex ways in which human activity may affect communities across temporal scales.
Walsh, W., Winsor, A. M., & Jakob, E. M. (2025). Web placement in grass spiders (Agelenopsis pennsylvanica) is driven more by artificial light at night than by prey. Animal Behaviour, 123365. https://doi.org/10.1016/j.anbehav.2025.123365