It is well-known that numerous animals, from arthropods to vertebrates, can sense Earth’s magnetic field and use this information to guide their movement. However, the specific mechanism responsible for a magnetic sense remains enigmatic. Although several putative mechanisms of magnetic sensing are often studied, a new, potentially unifying hypothesis has recently been proposed. This hypothesis posits that specific bacteria, called magnetotactic bacteria, are responsible for a magnetic sense through a symbiotic relationship with a host animal. More specifically, these bacteria, which manufacture their own chains of magnetite crystals to sense Earth’s magnetic field, could reside in specific nervous system tissues of animals and communicate magnetic information to the host. This presentation will summarize the hypothesis and discuss preliminary supporting data collected from metagenomic databases. This work combined with future experimental evidence will provide critical data to improve the understanding of how organisms use Earth’s magnetic field to inform their movements and the various novel ways in which symbiotic microbes govern important physiological traits of a host.