A team of scientists and engineers at The University of Texas at Austin has identified the first sensor of the Earth's magnetic field in an animal, finding in the brain of a tiny worm a big clue to a long-held mystery about how animals' internal compasses work. Animals as diverse as migrating geese, sea turtles and wolves are known to navigate using the Earth's magnetic field. But until now, no one has pinpointed quite how they do it. The sensor, found in worms called C. elegans, is a microscopic structure at the end of a neuron that other animals probably share, given similarities in brain structure across species. The sensor looks like a nano-scale TV antenna, and the worms use it to navigate underground.

"Chances are that the same molecules will be used by cuter animals like butterflies and birds," said Jon Pierce-Shimomura, assistant professor of neuroscience in the College of Natural Sciences and member of the research team. "This gives us a first foothold in understanding magnetosensation in other animals."

The researchers discovered that hungry worms in gelatin-filled tubes tend to move down, a strategy they might use when searching for food. 

When the researchers brought worms into the lab from other parts of the world, the worms didn't all move down. Depending on where they were from -- Hawaii, England or Australia, for example -- they moved at a precise angle to the magnetic field that would have corresponded to down if they had been back home. For instance, Australian worms moved upward in tubes. The magnetic field's orientation varies from spot to spot on Earth, and each worm's magnetic field sensor system is finely tuned to its local environment, allowing it to tell up from down.

The research is published today in the journal eLife.