image: The Australian Bogong moth Agrotis infusa (Lepidoptera: Noctuidae).
A major international study led by researchers from Lund University in Sweden has proven for the first time that certain nocturnally migrating insects can explore and navigate using the Earth's magnetic field. Until now, the ability to steer flight using an internal magnetic compass was only known in nocturnally migrating birds.
WATCH: The incredible journey of the bogong moth https://www.youtube.com/watch?v=Z7w44Ka0xXI
"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 one thousand kilometres. We show that insects probably use the Earth's magnetic field in a similar way to birds", says Eric Warrant, professor at Lund University.
Eric Warrant and David Dreyer at Lund University, together with colleagues from Australia, Canada, Germany, and the USA , studied the moth species Agrotis infusa, also known as the Bogong moth, in Australia.
The findings indicate that the insects use both visual landmarks in their flight path and the Earth's magnetic field, probably making their navigation more reliable.
The researchers 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 moths migrate over a great distance every year, from a large area in southeastern Australia to a specific area of small, cool caves high up in the mountains more than one thousand kilometres away. After a few months in a dormant state, they make the same journey back when summer is over. Besides the Bogong moth, only the North American Monarch butterfly migrates with equivalent precision.
The researchers focused on investigating how the Bogong moth knows 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 team members Barrie Frost and Henrik Mouritsen 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.
"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", says David Dreyer, adding:
"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."
Eric Warrant has many years of experience of researching animal night vision and how animals navigate in the dark. Nevertheless, the findings surprised him.
"I believed the studies would show that Bogong moths only use visual cues such as stars, the moon and landmarks to navigate. But that is not the case. They perceive the Earth's magnetic field in exactly the same way as birds do - and probably for the same reason."
The next step will be to find out how the moths, despite never having been to the caves before, know that they have arrived at their destination. The researchers also want to locate and characterise the insects' elusive magnetic sensor.