Researchers have discovered a surprising side effect of artificial lighting. An ordinary streetlight can lure thousands of tiny land-dwelling isopods into a gigantic, synchronized death spiral. The newly documented behavior observed in Israel is the first of its kind and suggests that artificial lighting can dramatically disrupt the instincts of small land-dwelling animals.
The research was led by doctoral student Idan Sheizaf under the supervision of Professor Ariel Chipman of the Hebrew University of Jerusalem. Published in ecology and evolutionThe study describes how land-dwelling isopods, relatives of crabs and shrimp known as woodlice and pill bugs, abandon their normally solitary habits and join giant circular formations containing more than 5,000 individuals.
Amazing discovery in northern Israel
The unusual behavior first became apparent after amateur naturalist Evitar Itzković noticed a huge swarm of isopods swirling in the Golan Heights on a summer night.
Researchers focused on the species dirty armadilloa little-studied isopod that usually spends its time hiding under rocks or damp leaf litter, where moisture helps prevent it from drying out.
Woodlice commonly swarm to conserve moisture, but scientists had never recorded coordinated movements on this scale. Until this work appeared, little was known about it. A.Dirty. This study also expanded the known range of this species. Previously, it had only been recorded in southern Syria and the Golan Heights. Researchers have now recorded it for the first time in the Jezreel Valley.
Experiment reveals the role of artificial light
To determine the cause of the strange circular march, the team tested several possible explanations, including magnetic fields and different types of lighting.
Despite the Golan Heights being known for its unusual magnetic properties, powerful magnets placed near the moving isopod had no effect. The animals continued to circle without interruption.
Ultraviolet flashlights attracted only a few isopods and did not cause swirling formations.
However, white light consistently produced dramatic behavior. When the researchers placed a white lamp with the light shining directly below them, the isopods repeatedly gathered together to form large rotating circles.
Experiments showed that the shape of the irradiation area is the most important. The vertical beam creates a circular light border on the ground. The isopod is drawn toward its edge and begins walking along its perimeter. As more individuals join, the movement reaches a tipping point and develops into a large, self-sustaining circular matrix.
Reflecting on the discovery, Idan Sheizaf said: “Group movement is common in the animal kingdom, but it was completely unexpected to see it in this way in isopods. The geometry of the modern world, especially the circular pools of light created by street lamps, seems to interact with the natural instincts of these creatures to produce a fascinating but potentially harmful emergent phenomenon.”
Why is the “death spiral” dangerous?
Although the spiral formations are visually striking, researchers believe they represent an unintentional trap created by artificial nighttime light (ALAN) rather than natural social behavior.
Most of the participants were females, and many were carrying eggs, so it is unlikely that the gathering was related to mating. Rather, there is evidence that artificial light disrupts animals’ normal instincts.
The consequences can be serious. In one observation, centipedes preyed on isopods that distracted them while they remained trapped in swirling strata. Streetlights can pull these animals out of their protected habitats and keep them moving in circles, leaving them vulnerable to predators and wasting the energy they need to survive.
The findings highlight how even simple changes in the environment, such as installing streetlights, can reconstruct ancient behaviors in small animals that are often overlooked.
