On spring nights, bogong moths migrate to the Australian Alps, travelling distances of more than 1000 kilometres to reach the cool mountain caves where they spend their summers aestivating. But how does the moth navigate from its winter breeding grounds to the alps? Tests in a flight simulator found moths found their way by the stars and moon, but became disoriented when researchers deliberately misaligned the sky and the Earth’s magnetic field. That magnetic field is crucial to the moths’ ability to find their way, making bogong moths the first nocturnal insect known to use magnetic sensitivity as a tool in long-distance migration. (Birds have long been known to navigate using the Earth’s magnetic field.) Do other insects have an internal compass tuned to the Earth’s magnetic field? Study co-author Eric Warrant, a sensory physiologist from Lund University in Sweden, says monarch butterflies, which migrate by day across the United States to overwinter in Mexico, may also have some magnetic sensitivity, but their primary compass is the sun: “Bogong moths must rely on the Earth’s magnetic field because the moon is a very variable and unreliable cue compared to the sun—which is a very constant cue day after day.”
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