Published on July 22nd, 2009 | by Bryan Nelson2
14,000km Dragonfly Migration Discovered, Longest of Any Insect
A remarkable dragonfly migration stretching between 14,000 and 18,000 kilometers has been discovered which spans the Indian Ocean.
The migration is by far the longest known insect migration, dwarfing the 7,000km journey of monarch butterflies. Millions of dragonflies make the epic migration every year, which spans from India to the Maldives, the Seychelles, Mozambique, Uganda and back again.
Perhaps the only thing more amazing than the migration is that it has somehow dodged scientific discovery until now. “This just illustrates how little we still know about the natural world,” said Charles Anderson, discoverer of the mass migration.
Charles Anderson is a biologist who works at the Maldives Marine Research Center. Upon noticing the millions of dragonflies arriving each year, he decided to ask around about it. The event is well known to locals, but no one he spoke to seemed to know where the dragonflies come from.
Their appearance there is particularly strange because the Maldives are located so far away from any other land mass, up to 600-1000km across the Indian Ocean from India. Furthermore, the 1,200 coral atolls and small islands which make up the Maldives archipelago house very little fresh water, which the dragonflies would require to breed and complete their life cycle. So what are they doing there, and in such large numbers?
Anderson tracked their arrival and departure dates and found that it coincided with an unusual weather system called the Inter-tropical Convergence Zone. Once a year from October to December, winds over the Indian Ocean suddenly shift direction and move southward from India toward the Maldives. He therefore deduced that the dragonflies were using those winds to glide over the remarkable distance. That journey is incredible enough, but the dragonflies only stay for a few days in the Maldives before moving on. Where do they go next?
It turns out that large numbers of dragonflies– the same species which make the journey from India to the Maldives– start to arrive on the Seychelles islands in November and December, some 3,000-4,000 kilometers from their original location in India.
And that’s still not the end of their journey. It is also known that the dragonflies appear in large numbers throughout eastern and southern Africa, as far south as Mozambique by January. Then in March and April they begin to appear in large numbers in Uganda, most likely on their way back up to India– just in time for the next monsoon season.
All in all, the epic adventure spans a total of 14,000-18,000 kilometers, and the journey appears to follow the rains, from the monsoon season in India to the rainy season in eastern and southern Africa. The swarm of dragonflies complete a total of 4 generations by the time the entire migration is completed. Furthermore, the trip is mirrored by the migratory paths of a number of insect-eating bird species, which scientists now know must feed on the dragonflies as they travel.
It’s been known for a few years that dragonflies were capable of long distance migrations, and that their migrations often resembled that of birds. But no one expected this. “There are earlier records of swarms of dragonflies flying out to sea, and at sea,” Anderson said.
“But it was always assumed that those dragonflies were doomed. Which says rather more about our earth-bound lack of imagination than it does about the globe skimmers’ extraordinary flying abilities.”
Source: BBC NEWS
Image Credit: kretyen on Flickr under a CC License