Woodlice Form Rotating "Death Spirals" Under Streetlights

On warm nights in northern Israel, something deeply strange happens under the glow of streetlights: thousands of woodlice begin to move in perfect, rotating circles. These "death spirals" — also called "isopod mills" — can involve over 5,000 individuals at a time, spinning in a hypnotic geometric pattern that seems almost intentional.

But it is not intentional. It is a trap.

In May 2026, researchers from Hebrew University of Jerusalem published their findings in the journal Ecology and Evolution. The phenomenon was first observed in the Golan Heights by amateur naturalist Eviatar Itzkovich and subsequently investigated by PhD student Idan Sheizaf and Professor Ariel Chipman.

The cause? The geometry of white artificial light at night (ALAN). When a vertical streetlamp illuminates the ground, the woodlice — specifically the species Armadillo sordidus — form a circular boundary around the lit area and begin following its edge. As more individuals join, the movement intensifies into a continuous rotating mill.

The swarms are predominantly female, many carrying eggs, ruling out mating as an explanation. Instead, the researchers believe it is a disruption of natural instincts — a kind of behavioural short-circuit caused by an environment never encountered in the species' evolutionary history.

Key Evidence

• Published in Ecology and Evolution (May 2026)
• Over 5,000 individuals observed in single swarms
• Triggered by geometry of white artificial light, not just brightness
• Predominantly female swarms, many carrying eggs
• Makes woodlice vulnerable to predators and causes energy loss

The Rational Explanation

This is a classic example of an emergent property: individual woodlice following a simple behavioural rule (stay near the light edge) producing a complex collective pattern (rotating mill) when multiplied across thousands of individuals. Similar "death spirals" have been observed in army ants. The behaviour is not mysterious — it is the unintended consequence of human technology interacting with animal instinct.

What We Don't Know

How widespread is this phenomenon? The study focused on northern Israel, but ALAN is global. Are woodlice and other nocturnal species experiencing similar behavioural disruptions in cities worldwide? And what are the long-term ecological consequences of these artificial patterns?

The Rabbit Hole

This is part of a broader pattern: human infrastructure creating bizarre new behaviours in the natural world. From birds singing at artificial dawn to sea turtles confused by beachfront lighting, the built environment is rewriting animal behaviour in real-time. The woodlice mills are simply the strangest example yet documented.