Lobsters navigate with magnetic positioning system, study shows

Spiny lobsters possess a remarkable navigational sense based on an ability to read small variations in the Earth’s magnetic field, experiments conducted by University of North Carolina at Chapel Hill scientists show. The new work is the first to demonstrate that at least some invertebrate animals, which many people consider primitive underachievers biologically, possess navigational skills rivaling those of sea turtles and homing pigeons.

“After spending daylight hours inside coral reef crevices, spiny lobsters emerge at night to forage over large areas before returning in darkness to the same den,” said biology doctoral student Larry C. Boles, first author of a scientific paper about the study. “Something in a lobster’s nervous system allows it to monitor the invisible magnetic field that exists throughout its underwater habitat and to exploit small differences in the fields found at different locations to chart a course back home.”

That seemingly uncanny mechanism — something like nature’s own global positioning system — mirrors what baby sea turtles and birds can do as shown by earlier studies at UNC and elsewhere, Boles said.

Spiny lobsters are a tropical species and are not the clawed lobsters most people are familiar with from restaurants and grocery stores, he said. In the past, many have assumed that a complex navigational ability would require a fairly sophisticated nervous system and that the brains of invertebrates might not be up to the task.

A report on the findings appears in the Jan. 2 issue of the journal Nature. Dr. Kenneth Lohmann, L. G. Hoggard distinguished associate professor of biology at UNC and Boles’ mentor, is co-author.

The project began when the two began wondering how lobsters find their way back to their dens at night in complete darkness. To test the animals’ homing abilities, they captured lobsters at various sites in the Florida Keys and transported them to a marine laboratory about 10 miles away.

“During the trip, we tried to confuse the lobsters by keeping them in sealed boxes, turning them constantly and following indirect routes to the lab,” Boles said. “When the trip was over, we tethered the lobsters to an electronic tracking system that monitored the direction toward which they tried to walk.”

“We couldn’t believe it,” said Lohmann. “The lobsters had never been to the lab, and we expected them to be completely lost. Instead, they walked each time in directions that pointed toward home. They somehow knew where they were.”

To determine if the crustaceans used the Earth’s magnetic field to determine their position, the researchers built a large magnetic coil around the lobster tank. The coil allowed them to produce magnetic fields identical to fields found at other locations away from the test site.

“We tried to trick the lobsters into thinking they were somewhere else,” Boles said. “We put them in magnetic fields found at locations a considerable distance from where they were actually being tested.”

One group was exposed to a field that exists in a location north of the test site, he said. A second group was tested in a field comparable to one found at an area to the south. Sure enough, the crustaceans were not fooled.

Lobsters tested in the field measured at the northern location walked south, while those exposed to the field from the south walked north. Thus, lobsters responded to each field by walking in a direction that would have led them home had they actually been at the location where each field naturally occurs.

The results show that lobsters can tell where they are by using the magnetic fields they encounter, Boles said. In essence, they have a magnetic “map” that enables them to navigate over long distances.

“Our findings will surprise a lot of people,” Boles said. “They provide some of the strongest evidence yet that animals have and use magnetic maps. That’s the reason Nature, one of the world’s top scientific journals, accepted our paper for publication.”

It is hard to convey what a leap it is to go from something like a migratory bird to a lobster, which is like a big ocean insect, he said. People do not generally ascribe much mental ability to invertebrate animals.

Lohmann, who several years ago showed that baby sea turtles have a similar ability, said the work probably would spur other scientists to investigate animal migration and navigation.

“This is an exciting area of research right now,” he said. “The picture that is emerging is that magnetic positioning systems are real, and they may be widespread among animals.”