The diagram to the right shows the orientation of lobsters tested in magnetic fields replicating those that exist at two different geographic locations (marked by stars on the map). The arrow outside each orientation diagram indicates the direction that lobsters would be expected to orient if homing from the fictive locations. The open triangle outside each orientation diagram indicates the actual direction to the capture site from the test site. In each case, lobsters responded as if they had been displaced to the locations marked by the stars rather than by orienting in the direction that was actually toward the capture site. Lobsters exposed to the field of the northern site walked south-southwest. Those exposed to the field of the southern site walked approximately north. These results indicate that lobsters can distinguish between magnetic fields that mark different geographic locations within their environment. Moreover, they responded to each field by orienting in a direction that would have led them toward the capture site had they actually been at the location where each field naturally occurs. In effect, the lobsters were tricked into thinking they were at a location where they were not.

• These results provide strong evidence that spiny lobsters determine their geographic position by using information from the Earth's magnetic field. In effect, the animals have an underwater GPS system based on geomagnetism.
• This ability, known as a magnetic map sense, enables lobsters to navigate through a complex reef environment during nightly foraging trips in complete darkness. By sensing subtle differences in the invisible magnetic fields that mark different locations, lobsters can guide themselves reliably around their underwater habitat.
• Although lobsters and other invertebrate animals have traditionally been regarded as simple creatures with small brains and limited sensory abilities, the navigational system of lobsters is actually among the most complex and sophisticated in the animal kingdom.