On warm summer nights in the Golan Heights, thousands of small woodlice gather beneath streetlights and walk in endless circles until they die. An amateur naturalist from Kibbutz Gshur noticed this strange behaviour near his home and brought it to scientists at the Hebrew University of Jerusalem. Their research, published this spring in Ecology and Evolution, is the first formal study of this deadly phenomenon in woodlice.
The creatures involved are Armadillo sordidus, small harmless crustaceans normally solitary and shy. Yet beneath certain streetlights, up to 5,500 individuals have been observed marching together in perfect circles. PhD student Idan Sheizaf led the investigation to understand why.
The team discovered that the geometry of modern LED streetlights is the cause. When white light shines straight down from above, the woodlice are drawn to the circular edge of the lit area and follow each other in an endless loop. They walk until exhaustion kills them. Horizontal light, by contrast, causes them to gather but not to spiral.
The phenomenon mirrors the famous "ant mill" documented in 1921, where army ants followed each other in circles until they died. What makes this woodlice spiral especially concerning is that many of the dying animals are females carrying eggs. Additionally, centipedes hunt the distracted creatures, picking them off one by one.
Light pollution from streetlights has long been known to harm insects globally. This is the first time researchers have shown how it can trap an entire population in a fatal loop.