Monday, November 6, 2017

Dragonfly that Crosses the Seas to Africa - Article on The New Indian Express Newspaper about Dragonfly Migration (October 22, 2014) )

This evening, look up and you will see Globe Skimmer Dragonflies (Pantala flavescens), famous in Kerala by the name ‘Onathumbi’, heading towards the south or south-western direction. A city-based group of nature watchers has started monitoring the flight of the Globe Skimmer, believed to be the longest migration trail of any insect. And guess where it is all headed to? Africa.

 Members of the group, Travancore Natural History Society (TNHS), are observing the phenomenon with interest. Eldho Pachilakadan, a TNHS member, was the first to notice a large aggregation of dragonflies. Having spotted it at a point between Cherai and Njarakkal coasts in Ernakulam district, he followed the trail. There were more aggregations on the way, apart from small clusters, confirming that the migration had begun. 

 “I counted around 1,500 Globe Skimmers crossing a point in Cherai in a minutes’ time. When these reach an aggregation, their number is to the tune of crores and cannot be counted. The number is so large that even Swallows and Bee-eaters, which on a better day would eat them, would hesitate to come close,” says Eldho, an architect who is more an environmentalist now.  
 Swarms of Globe Skimmers which leave from South India are spotted along the shores of Maldives in the month of October, according Charles Anderson, a biologist based in the place. He started collecting data from observers in Maldives, India as well as vessels in the sea. In 2009, he published a study saying that the insects migrated from South India to Africa. However, this was based on circumstantial evidence. 

 Later, the scientist, with Keith Hobson and David X Soto, started studying the stable-hydrogen isotopes in the wings of dragonflies. These isotopes are absorbed into the blood during the insect’s larval stage, and are heavily influenced by the water body in which the larva was bred. Their paper published in 2012 suggested that there is a high probability of the dragonflies in Maldives having arrived from as far as the Himalayas.

 “They arrive at the beginning of the Onam months and then breed in the fresh waters of the state. In the state their distribution is from the lowlands to the crest of the Western Ghats. The duration of larval stage is around one month. Some of the offspring breed here while most embark on a pilgrimage to Africa,” says Dr Kalesh Sadasivan, PRO of TNHS.

 The average speed of the dragonflies is 5 metres per second - not very impressive. So how do the insects traverse oceans and continents? Scientists think that they achieve this by riding high-altitude winds. However, this does not mean that the insect which leaves from Kerala would reach Africa. How can they? Their lifecycle lasts not more than five months. What happens is a multi-generational migration - the role of migration is inherited by the next generation. By the time the swarm reaches Africa, it would be made of completely new members.    

 “Pantala plays an important role in curbing the mosquito menace in the state. They are carnivores and catch mosquitoes in mid-flight. The larvae are also effective mosquito larval predators,” says Kiran C G, a member of TNHS who wrote the book ‘Dragonflies and Damselflies of Kerala’. “There will be an upsurge in the number of mosquitoes in the coming months,” he adds

Original Article - Dragonfly that Crosses the Seas to Africa - The New Indian Express October 22, 2014

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