Earthworms don’t need eyes to sense direction, but they may need the planet’s magnetic tug to keep moving normally. In carefully controlled lab tests, researchers found that red earthworms crawled far less when the surrounding magnetic field was dialled down to almost zero.
The team built a simple, reproducible setup: worms wriggled through see-through (transparent) soil inside coils that either left Earth’s natural field intact or cancelled it out. Video tracking then measured how much ground each animal covered. The result was striking — movement dropped in the weakened field, and the effect showed up within the first minute and held across trials and soil types.
As the authors put it, earthworms “move significantly less when held in a near-zero magnetic field,” and this outcome was “highly reproducible.”
To ensure that intensity, rather than an oddity of the equipment, drove the change, the researchers also rotated the magnetic field so that “north” pointed west, while keeping its strength close to normal. Worms moved about the same under this rotated field as they did under the natural one. That helps rule out confounding factors and supports a simple conclusion: it’s the very weak field that saps activity.
“All these results support that cumulative distance is strongly reduced when the Earth’s magnetic field is reduced to near zero,” the team writes.
Direction was a subtler story. In one set of trials, groups of worms showed a shared directional bias that shifted toward the weak field’s westward orientation, hinting that they can, at times, align with magnetic cues. But that pattern didn’t repeat in later tests. The researchers are cautious here, noting that any collective direction can be shaped by many factors, from small differences among individuals to the layout of the test room.
Why does any of this matter? Magnetoreception (sensing magnetic fields) has been documented across animals, yet the biological “sensor” remains unknown. Birds are the classic model, but they’re hard to test and results can be noisy.
Earthworms offer an elegant alternative: easy to keep, free from sky cues, and trackable in transparent soil. The new protocol turns a decades-old puzzle into a classroom-simple experiment that other labs can copy. It doesn’t solve the mystery of the magnetic sense, but it gives researchers a reliable lever to pull.
Journal Reference: Biology Letters DOI: 10.1098/rsbl.2025.0213
