Surfacing in the light
Cai, J., Bennie, J. & Gaston, K.J. 2026. Brightened nights, altered earth: artificial light reshapes activity rhythms in an earthworm and soil processes. Biological Conservation 313, 111616.
Artificial light at night (ALAN) is a global environmental disruptor, impacting natural dark-light cycles, with effects reported on the activity rhythms of diverse taxonomic groups and some associated ecosystem processes. Yet, impacts on soil-dwelling animals that are nocturnally active aboveground remain understudied. Here, we experimentally exposed the earthworm Lumbricus terrestris L. to ALAN (20 lx) in a glasshouse to see whether and how this would affect surface activity during nighttime and crepuscular periods (sunset + sunrise), and consequently soil processes, compared to the naturally lit condition. We recorded overall surface activity of L. terrestris, and three finer categories: pre-surfacing activity, foraging, and over-surface exploration. During nighttime, ALAN reduced foraging and over-surface exploration in L. terrestris by 40.8 % and 65.9 %, but increased pre-surfacing activity by 137.7 %. In comparison, crepuscular surface activity generally increased, with foraging even surging up to 347.8 % at sunset. Whereas there was no detectable change in soil respiration, these ALAN-driven activity disruptions were accompanied by measurable changes in other soil processes: increased transport of surface litter into upper soil layers (+112.4 %) alongside reduced litter consumption (-32.3 %) and redistribution of soil aggregates across soil profiles. Our results also indicated signs of light adaptation in L. terrestris. Overall, our findings suggest that whilst long-term monitoring of ALAN capacity to alter rhythms of activity of this keystone ecosystem engineer and ecological consequences is necessary, the pronounced shifts in the short term nonetheless warrant immediate attention and should inform conservation strategies to preserve soil biodiversity and functionality in a rapidly urbanising world.