Researchers have uncovered a surprising side effect of artificial lighting: ordinary streetlights can lure thousands of tiny land dwelling isopods into giant synchronized “death spirals.” The newly documented behavior, observed in Israel, is the first of its kind and suggests that human made lighting can dramatically disrupt the instincts of small ground dwelling animals.
The study was led by PhD student Idan Sheizaf under the supervision of Prof. Ariel Chipman at The Hebrew University of Jerusalem. Published in Ecology and Evolution, the research describes how land dwelling isopods, relatives of crabs and shrimp that are better known as woodlice or pill bugs, abandon their normally solitary habits to join enormous circular formations containing more than 5,000 individuals.
A surprising discovery in northern Israel
The unusual behavior first came to light after amateur naturalist Eviatar Itzkovich noticed huge swirling groups of isopods during summer nights in the Golan Heights.
The researchers focused on the species Armadillo sordidus, a little studied isopod that typically spends its time hidden beneath rocks and damp leaf litter, where moisture helps prevent it from drying out.
Although woodlice commonly cluster together to conserve moisture, scientists had never documented coordinated movement on this scale. Before this work, very little was known about A. sordidus. The study also expanded the species’ known range. Previously, it had only been recorded in southern Syria and the Golan Heights. Researchers have now documented it in the Jezreel Valley for the first time.
Experiments reveal the role of artificial light
To determine what was causing the strange circular marches, the team tested several possible explanations, including magnetic fields and different types of lighting.
Strong magnets placed near the moving isopods had no effect, even though the Golan Heights is known for unusual magnetic properties. The animals continued circling uninterrupted.
Ultraviolet flashlights attracted only a small number of isopods and never triggered the swirling formations.
White light, however, consistently produced the dramatic behavior. When researchers positioned a white lamp so that its beam shone straight down, the isopods repeatedly gathered into large rotating circles.
The experiments showed that the shape of the illuminated area is what matters most. A vertical beam creates a circular boundary of light on the ground. Drawn toward that edge, the isopods begin walking along its perimeter. As more individuals join, the movement reaches a tipping point and develops into a large, self sustaining circular procession.
Reflecting on the findings, Idan Sheizaf said: “While collective movement is common in the animal kingdom, seeing it in this form in isopods was entirely unexpected. It appears that the geometry of our modern world — specifically the circular pools of light created by streetlights, is interacting with the natural instincts of these creatures to create a mesmerizing, yet potentially harmful, emergent phenomenon.”
Why the “death spirals” may be dangerous
Although the swirling formations are visually striking, researchers believe they represent an unintended trap created by artificial light at night (ALAN), not a natural social behavior.
Most of the participants were female, and many were carrying eggs, making it unlikely that the gatherings were related to mating. Instead, the evidence suggests that artificial lighting is disrupting the animals’ normal instincts.
The consequences could be severe. During one observation, a centipede preyed on the distracted isopods while they remained caught in the swirling formation. By pulling these animals out of their sheltered habitats and keeping them moving in circles, streetlights may leave them vulnerable to predators while also wasting energy needed for survival.
The findings highlight how even a simple change to the environment, such as installing a streetlight, can reshape ancient behaviors in small animals that often go unnoticed.