WASHINGTON: Scientists have for the first time found a sensor to detect the Earth's magnetic field in an animal after they discovered a tiny antenna-like structure in the brain of worms that acts like an internal compass to help them navigate.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 how they do it.Researchers at The University of Texas at Austin found the sensor in worms called C elegans, 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," Pierce-Shimomura said.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 did not 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.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 neuron sporting a magnetic field sensor, called an AFD neuron, in the worm was already known to sense carbon dioxide levels and temperature.The researchers discovered the worms' magnetosensory abilities by altering the magnetic field around them with a special magnetic coil system and then observing changes in behaviour.They also showed that worms which were genetically engineered to have a broken AFD neuron did not orient themselves up and down as do normal worms.Finally, the researchers used a technique called calcium imaging to demonstrate that changes in the magnetic field cause the AFD neuron to activate.Pierce-Shimomura suggested this research might open up the possibility of manipulating magnetic fields to protect agricultural crops from harmful pests.