Scientists have finally found out the reason behind the monarch butterflies’ spectacular annual migration from North America to Mexico.

A study into the insect’s genetic structure has provided the answer to the question which has baffled researchers for many years. This new study has shed light on the history and migration pattern of this beautiful orange and black winged insect.

“Prior to our work, monarch migration was thought by some to be a very recent phenomenon, but we have shown that it evolved millions of years ago,” study co-author Marcus Kronforst told AFP of the findings that he said “overturn past thinking about monarch butterflies”.

“I believe this raises the stakes considerably when we consider that we may be witnessing the end of an amazing biological phenomenon that these little insects have been carrying out every year for the past two million-plus years.”



The number of butterflies that travel such a huge distance has fallen sharply over the last few years. In 1996, about a billion of the fluttering insects known to scientists as Danaus plexippus, completed the gruelling north-south trip, but only 35 million in the past year, according to the study authors.

The drop has been blamed on deforestation, drought and a sharp decline ascribed to herbicide use in the milkweed plants on which they feed and lay eggs.

“You used to see huge numbers of monarchs, clouds of them passing by,” said Kronforst. “Now it looks quite possible that in the not too distant future, this annual migration won’t happen.”

At the same time, many groups that used to migrate are morphing into stationary populations.

Now, by sequencing genomes of 90 monarch butterflies from around the world, researchers have discovered a gene that plays a critical role in determining whether monarchs are migratory, along with new details about their origins, migratory behavior and coloring.

The scientists discovered that migratory butterflies had reduced levels of a collagen gene that is involved in forming flight muscles. By using a flight monitor, they also found that the migrators consumed less oxygen and had a lower metabolic rate, allowing them to fly long distances.

“I like to think of it as a marathon runner versus a sprinter,” Dr. Kronforst said. “The migratory ones are really marathon runners.”

While most monarchs are orange and black, a small percentage of those in Hawaii are white and black.

“There’s one spot in one gene where all the white ones are different from all the orange ones,” Dr. Kronforst said.

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