Bogong Moths Are First Bugs Known to Use Stars for Long-Distance Travel
Every spring in the Southern Hemisphere, Bogong moths migrate up to 621 miles (1,000 kilometers) from southeast Australia to spend the summer in cool caves in the Australian Alps. At the beginning of the fall, they fly back to their breeding grounds and die. Each moth undertakes the two-way journey only once in its life—so how does it know where it's going?
A team led by David Dreyer, a visiting research fellow in sensory biology at Lund University, suggests that Bogong moths may use the starry sky—among other tools—to navigate in the right direction. If this proves to be true, Dreyer and his colleagues claim it would make the Australian Bogong moth the first known invertebrate to 'use the stars for discerning specific geographical directions (that is, a direction relative to north) for directed long-range navigation to a distant goal,' the team wrote in a new study, published today in the journal Nature.
In 2018, the same researchers suggested that Bogong moths reach their destinations by both sensing Earth's magnetic field and by using unknown visual landmarks. In fact, as noted by a Nature News and Views article, some animals rely on several different navigational methods. To test whether the night sky plays a role in guiding the moths, the team captured the insects at the start of their migration and placed them in a planetarium-like simulator.
'By tethering spring and autumn migratory moths in a flight simulator, we found that, under naturalistic moonless night skies and in a nulled geomagnetic field (disabling the moth's known magnetic sense), moths flew in their seasonally appropriate migratory directions,' the researchers explained in the study.
As ancient seafarers would attest, the predictable positions of stars make them a reliable navigational tool. Nonetheless, scientists have previously documented only some night-migratory birds using starlight to find a specific geographical direction. Dung Beetles use the stars to travel in a straight line, but they are not migratory insects—they're not using stellar cues for long-distance travel like birds and Bogong moths do.
By analyzing the moth's brain, the scientists also demonstrated that neurons linked to vision 'responded specifically to rotations of the night sky and were tuned to a common sky orientation,' showing the greatest activity 'when the moth was headed southwards.' In other words, their brains appear to be wired to pick up on stellar cues.
However, the parts of the starry sky that moths specifically rely on for directions remain a mystery, especially since it is unclear whether moths can even see individual stars. The researchers theorize that the moths can likely see the Milky Way, while constellations, the Moon, and potentially dark features on the horizon might also serve as reliable navigational cues.
Ultimately, the study builds on the team's previous research by further illuminating the Bogong moth's directional toolkit. 'Our results suggest that Bogong moths use stellar cues and the Earth's magnetic field to create a robust compass system for long-distance nocturnal navigation towards a specific destination,' the researchers concluded.
The next time intense solar activity causes GPS blackouts, I bet we'll all be wishing we were Bogong moths.
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