Picture of David Weaver
Reading American monarch butterflies use their internal clock for sky navigation. The butterflies travel in the fall for winter from North America to Mexico. Although they primarily use the sun for orientation on this long flight, they use the internal clock to balance their course. The report American neurobiologists in the journal "Science" (Volume 300, p. 1303). During the journey from North America to Mexico, the position of the sun in the sky changes over time. This change can apparently balance the insects with the internal clock, so they stay on track. The scientists around Steven Reppert from the University of Massachusetts in Worcester have observed this with the aid of a special flight simulator, which recorded the flight direction of the insects with a video camera and a computer. Their results are the first evidence that insects need their internal clock for sky navigation, the researchers say.

After the butterflies had lived in a light-dark cycle that corresponded to the light in the fall (light from 7 to 19 o'clock), the insects turned southwest towards Mexico when the biologists exposed them again to the daylight. However, if the monarch butterflies had lived in an earlier rhythm (light from 1 to 1 pm), they flew in the wrong direction, to the southeast. Constant light confused the animals completely: The butterflies seemed to have lost their sense of time and then flew right to the sun.

Biologists have long been pretty sure monarch butterflies navigate the sun. But how they correct their direction of flight every day is hardly known. It has long been assumed that the internal clock plays a role in this. Reppert and his team have now proven that this timepiece is absolutely essential for orientation. How it works in detail and how time finally regulates the spatial information, the scientists still need to clarify.

Only every fourth or fifth generation of monarch butterflies set out on a long journey to Mexico this fall. This behavior is thus not learned, but instinctive. The orientation skills of these butterflies therefore seem to be simpler than those of bees, for example, who are constantly learning their way to feed. display

ddp / bdw? Cornelia Pfaff

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