Whilst other invertebrates also make use of the night sky, only A. infusa moths appear to do so for long-distance navigation.
In addition to the Earth’s magnetic field, Agrotis infusa moths have been found to use the night sky to navigate during migration.
During their 1,000-kilometre migration, Australian Agrotis infusa moths navigate by the stars. This makes them the first known invertebrate species to use a star compass for long-distance navigation, an international research team claims on 18 June in Nature.
Every spring, the moths escape the scorching south-east of Australia to spend the summer in cool mountain caves. In autumn they return, reproduce, and then die. Individual moths therefore make the entire journey only once; the researchers reasoned that a learned sense of direction is therefore out of the question. It was already known, however, that A. infusa moths can navigate using the Earth’s magnetic field.
Flight tunnel
That they also draw on information from the night sky, in addition to the Earth’s magnetic field, emerged from experiments using a flight tunnel. In it, researchers recreated the Australian night sky. Moths caught in spring or autumn fly in the correct seasonal direction inside such a tunnel when presented with a realistic star field – even when the researchers block the Earth’s magnetic field within the tunnel. When the researchers rotate the orientation of the stars by 180 degrees, the moths fly more or less straight in the opposite direction. When presented with a randomly generated star field, they lose their sense of orientation and fly in no particular direction.
Whilst other invertebrates also make use of the night sky, only A. infusa moths appear to do so for long-distance navigation. Dung beetles, for example, use the stars only to move in a straight line – the direction of that line is of no further consequence to them. It is known, however, that monarch butterflies use a celestial body for orientation in addition to the Earth’s magnetic field; in their case, the sun.
Compass
Visual neurons play an important role in the moths’ star navigation, as the researchers discovered in a follow-up experiment. These neurons fire more strongly when a moth sees a star field in a specific orientation. The researchers believe this could be the neural basis for the internal star-based compass.
Exactly which aspect of the night sky the moths use remains unclear for now. The Milky Way is, in any case, clearly visible in Australia and shines particularly brightly in the south, the researchers note – presumably something that the moths can also perceive readily.