Artificial lighting at night is a growing worldwide phenomenon that can negatively impact flora and fauna in the surrounding area. With new technology, there is now opportunity for change: newer LEDs can emit specific wavelengths of light that may be less ecologically damaging. In this study, we aim to describe the circadian spectral sensitivity of two phylogenetically distant urban spider species with similar life histories, the Araneoid Parasteatoda tepidariorum and non-Araneoid Pholcus manueli, to determine differences between them. We exposed these spiders to progressively dimmer levels of white, blue, green, or red light. Despite evidence that spiders lack visual sensitivity to red light, we found that not only could both species entrain to the dimmest red light, P. tepidariorum had stronger entrainment to green and red light than white light. This study suggests that wavelength selection for ALAN will require a nuanced approach considering the sensitivities of individual local species.

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