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