Australian moths use the stars as a compass on 1000-km migrations

An Australian butterfly that migrates more than 1000 kilometers to request a respite by summer heat is the first invertebrate known to use the stars as a compass on long trips.

Each spring, billions of Bogong butterflies (Agrotis Infusa) Travel from various parts of southern Australia to cool the caves in the Australian Alps after spending the winter as a caterpillars feeding on vegetation. Once in the caves, they have a long period of inactivity, called Estivation, before returning to their breeding grounds.

It has been a long time a mystery exactly how these butterflies, whose figures have collapsed in recent years, have sailed so far to these high country caves, explains Andrea Adden at the Francis Crick Institute in London.

Previous studies have shown that they are able to use the electromagnetic field of the earth, but only in combination with benchmarks they can see. Adden and his colleagues wanted to discover which other clues butterflies can use to navigate.

“If you go to the Australian bush, where these butterflies live and look around the night, one of the most striking visual benchmarks is the milky way,” she said. “We know that day migratory insects use the sun, so testing the starry sky seemed to be an obvious thing to try.”

To do this, the team caught butterflies during their migration using light traps and took them to a laboratory. There, the insects were placed in a perspex arena and an image of the night sky was projected on a screen above them. The butterflies were attached inside the arena, but could choose a flight direction according to the image of the sky. The researchers used a device called Helmholtz coil to essentially cancel the magnetic field of the earth.

The tests have shown that butterflies use a stellar compass, explains the member of the Eric Mandate team at the University of Lund, Sweden. “When butterflies attached were placed in a very realistic local starred night sky, they stole in their inherited migratory direction,” he said. “They did it only with the help of these stars – all the other visual clues, as well as the magnetic field of the earth, were absent.”

When the team turned the starry sky of 180 degrees, the butterflies stolen in the opposite direction, and when they redistributed natural stars at random through the image, they were completely disoriented.

In a second experience, butterflies were fixed in place with a very thin electrode inserted in their brain. This revealed changes in the neuronal activity of the butterflies when the image of the projected sky was turned.

Although the beetles use the milky way of staying on the same rolling on short distances, no insect was known to use celestial navigation for migration so far.

“Bogong’s butterfly is the first invertebrate that we know who is able to use the stars like a compass for long -distance navigation towards a distant destination to which it has never been before,” explains Mandate. “Only humans and certain species of night migratory birds are known to have this capacity.”

Another insect famous for long -distance migration, the monarch butterfly (Danaus plexippus), use the sun to navigate, taking into account at the time of day.

Cody Freas at Macquarie University in Sydney, Australia, says it is remarkable what insects can do with a fairly simple visual system. “Stellar navigation really presents the capacities of these small eyes composed in night insects to navigate different indices – sun, moon and stars – as well as to work even in extremely low levels of light,” explains Freas.