Like many migrating birds, numerous species of nocturnal moths undertake long-distance migrations at night. Each spring, billions of Bogong moths (Agrotis infusa) escape hot conditions in different regions of southeast Australia by making a migration of over 600 miles (1,000 km) to cool caves in the Australian Alps; after a few months in a dormant state, the insects make the same journey back when summer is over. A new study led by Lund University shows that the moths can sense the Earth’s magnetic field and use it to steer their migratory flight behavior.
“Our findings are the first reliable proof that nocturnally active insects can use the Earth’s magnetic field to guide their flight when migrating over 600 miles,” said Lund University’s Professor Eric Warrant, co-lead author of the study.
“We show that insects probably use the Earth’s magnetic field in a similar way to birds.”
Professor Warrant and co-authors studied Bogong moths in Australia and focused on investigating how the moths know in which direction to fly.
They found answers by capturing the moths in flight and placing them in a flight simulator where the insects were free to fly in any direction they chose.
The flight simulator — invented by the team for studying navigation in Monarch butterflies — was in turn placed in a system of magnetic coils which allowed the researchers to turn the magnetic field in any direction. In addition, they were able to show visual landmarks to the moths.
The results, published in the journal Current Biology, indicate that the moths use both visual landmarks in their flight path and the Earth’s magnetic field, probably making their navigation more reliable.
“By turning the magnetic field and the landmarks either together or in conflict with each other, we were able to investigate how the Bogong moths use magnetic and visual information to direct their flight,” said co-lead author Dr. David Dreyer, also from Lund University.
“When the magnetic field and the landmarks were turned together, the moths changed their flight path in an equivalent manner.”
“However, if the magnetic field and the landmarks were turned in conflict with each other, the moths lost their sense of direction and became confused.”
“We believe that moths in northern Europe may use the Earth’s magnetic field in an equivalent manner when flying over the Alps to the Mediterranean,” the researchers said.
They now plan to find out how Bogong moths, despite never having been to the caves before, know that they have arrived at their destination. They also want to locate and characterize the insects’ elusive magnetic sensor.
David Dreyer et al. The Earth’s Magnetic Field and Visual Landmarks Steer Migratory Flight Behavior in the Nocturnal Australian Bogong Moth. Current Biology, published online June 21, 2018; doi: 10.1016/j.cub.2018.05.030