Scientists have known for decades that many animals use the Earth’s magnetic field for navigation. It’s less clear how they do it. A new study suggests earthworms may be a good way to figure it out. (This story first aired on All Things Considered on October 15, 2025.)
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Scientists have known for decades that some animals use the Earth’s magnetic field to help them navigate. Think of it as an internal GPS. But how it all works remains unclear. NPR’s Nate Rott reports on a new study which suggests earthworms may help provide an answer.
NATE ROTT, BYLINE: For the better part of a decade, behavioral ecologist Yoni Vortman’s research into magnetoreception – which we’ll talk more about in a minute – focused on birds. He recently switched to earthworms because, well, I’ll let him tell you.
YONI VORTMAN: I got to earthworms because I was kind of frustrated with birds, actually.
ROTT: (Laughter) Birds were doing you dirty, or what?
VORTMAN: Birds are like – you know, like a border collie. You try to do an experiment with them, and they jump towards the light, and a lot of things really interfere with them. I don’t know. If you have a dog…
ROTT: I do have a dog.
VORTMAN: …Then you know that you can try to train him to something, but then if he hears a noise, he’s going the other direction. And birds are like flying dogs.
ROTT: Earthworms are less distractible. They don’t have eyes or ears. And when you’re trying to determine how a species chooses where to go and what sense they’re using to make that decision, it’s easier when there are fewer inputs. So with worms…
VORTMAN: The intuition of most biologists is that earthworms move randomly. They don’t really navigate.
ROTT: But Vortman, who works at Tel-Hai Academic College in northern Israel, says when you consider that to move, earthworms have to literally eat dirt, expending a lot of energy…
VORTMAN: Then of course they don’t move randomly. And they need to navigate somehow, and the magnetic sense is the perfect thing if you navigate underground.
ROTT: The magnetic sense – magnetoreception, if we want to be fancy – is an animal’s ability to detect the Earth’s magnetic field. Scientists have found that all sorts of animals – not humans, but sea turtles, sharks, salamanders and birds, just to name a few – have this internal compass, this sixth sense.
VORTMAN: But somehow, amazingly, it’s the only sense that we don’t know where is the sensor.
ROTT: In other words, we know eyes are for seeing, ears for hearing. So what are they using to detect magnetic fields? Scientists have many theories. Maybe it’s biochemical reactions detecting magnetism. Maybe it’s electroreceptors. It’s all very heady. Vortman’s current hypothesis for worms is a symbiotic magnetic bacteria, which he says is for another paper and another discussion. But he says the paper he just published in the journal Biology Letters, showing that worms have this magnetic sense too, could really help scientists answer the broader question.
VORTMAN: Many things that we cannot do with birds or sea turtles, we can do with earthworms.
ROTT: For example, if you want to sample 40 sea turtles to understand how they’re navigating, it’s difficult and expensive.
VORTMAN: If you want to sample 40 earthworms – I don’t know – you can go to the next fishing store, right?
ROTT: They’re ubiquitous, cheap and, as we now know, a heck of a lot easier to work with than birds. Nate Rott, NPR News.
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