Monarch butterflies are well-known for their lengthy annual migration each fall from Canada to Mexico (and vice-versa in the spring) without losing their way for about 3,000 miles. As the length of these trips exceeds by far the lifetime of any given butterfly, it is strictly a one-way trip for each butterfly. So how do they return to the same locations over several generations? This was a mystery, until an international team of scientists finds the answer, revealed in this news release from the Hebrew University of Jerusalem. These researchers have found that monarch butterflies "have special photoreceptors for ultraviolet (UV) light in their eyes which provide them with their sense of direction." Without UVs, they get lost. Read more...
Before going further, here is a beautiful photograph of one of these monarch butterflies (Credit: Linda Thomas).
Here is a link to a larger version of this picture which comes from the Brookside Gardens Butterflies picture set of Linda Thomas on Flickr.
Here are some excerpts of the news release mentioned above.
The phenomenon of long-range bird migration is a well-known one, but not in the insect world. Also, among birds their migration route is a round-trip one, which they make more than once in their lifetimes, while for the monarch it is strictly a one-way trip for each butterfly. How do these creatures do it?
The mystery of the mechanisms involved in this remarkable phenomenon has been resolved by a team of scientists who did this by exploring the infinitesimal butterfly brain and eye tissues to uncover new insights into the biological machinery that directs this delicate creature on its lengthy flight path.
And here are some more details about the findings.
While light in general is essential to the functioning of the "biological clock" in the butterfly brain – governing its metabolic cycles, including its "signal" to migrate -- the researchers discovered that it is specifically the ultraviolet band of light that is crucial to the creature's orientation. The butterflies have special photoreceptors for ultraviolet (UV) light in their eyes which provide them with their sense of direction.
They proved that this ultraviolet "navigation" is crucial by placing butterflies in a "flight" simulator. When a UV light filter was used in the simulator, the butterflies lost their orientation.
For much more information, this research work has been recently published by Neuron under the title "Connecting the Navigational Clock to Sun Compass Input in Monarch Butterfly Brain" (Vol. 46, Issue 3, Pages 457-467, May 5, 2005). Here are two links to the abstract and the full paper (PDF format, 11 pages, 573 KB).
But if you prefer to simply know more about the monarch butterfly in plain English, here is a link to this page on Wikipedia -- which doesn't mention this latest discovery. Should I update this Wikipedia page? I have to think about it.
Sources: The Hebrew University of Jerusalem, August 8, 2005; and various web sites
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