Monarch butterflies use internal compass to find their way

Monarch butterflies at the El Rosario Butterfly Sanctuary outside of Angangueo, Mexico.
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Researchers believe the insects, which are rare visitors to the UK but are commonly found in North America, have an inbuilt biological compass that allows them to sense the direction of the Earth's magnetic field. Previously it was believed that the butterflies simply used the position of the sun to work out the direction they needed to travel, but it did not explain how they were able to continue travelling in the right direction even on cloudy days.

Biologists have found the butterflies have a pair of molecules in their brains that are sensitive to the Earth's magnetic field in much the same way as a compass and they can use these in combination with information from the position of the sun. They think that when changes in daylight during the summer that indicate the approach of winter cause these magnetic molecules to be switched on and so help the butterflies to orientate themselves in a south to south west direction.

Professor Steven Reppert, a neurobiologist at the University of Massachusetts who has been studying the monarch's brain, said: "The biology of the awe-inspiring fall migration of the monarch butterfly does scream out to be understood. "They travel very long distances and it is remarkable they know which direction to go. We think that they primarily use the sun to navigate, but it is known that on overcast days, they still travel in the correct direction. "The magnetic compass may serve as a back up system to keep the butterflies on track when they can't see the sun."

The migration of monarch butterflies is considered to be one of the most remarkable natural phenomena on the planet but their numbers have been in rapid decline.

The insects are typically found in the eastern US and south east Canada where they spend the summer months before flying south to a single spot in central Mexico on top of the Michoacán mountains for the winter. The journey can see them travel up to 3,000 miles. At these wintering sites they cluster on top of trees in their millions and the air is full of the sound of the rustling of their wings. In the Spring they make the return journey.

The insects are occasionally sighted in the south of the UK, usually after being blown of course during their migration, while there are also populations of monarch butterflies in the Canary Islands and on mainland Spain.

Individual butterflies can survive between two and eight months. Some butterflies make the whole trip but others lay eggs and die on the journey leaving offspring to complete the journey. This ability to continue travelling in the same direction to the same spot year after year has been a mystery for decades.

Due to their relatively short lifespan, however, the butterflies do not learn their route and instead their navigational abilities appear to be part of a genetic programme that sees them make the journey each year.

More: http://www.telegraph.co.uk/earth/wildlife/7855868/Monarch-butterflies-use-internal-compass-to-find-their-way.html

back in 1971 or 72.

One of the most mind blowing experiences that I have ever had.

Really amazing how many butterflies there are at times.