Dragonfly Mooring

-Brian Mendonça



A murky monsoon morning

A swarm of dragonflies above

What must this portend?

Soundlessly, they lay siege to my roof

Like a thousand possibilities

On a September day.


(5 September 2010


L1/ 105 B terrace,


Kalkaji New Delhi)



Note:

The appearance of migratory birds is often considered to foretell approaching rains. But migratory insects also may arrive in huge numbers, either singly or in swarms staggered over the days preceding the arrival of rains. Arrival of these less conspicuous organisms often goes unnoticed. This oversight may soon be changing with the recognition of a migration of dragonflies across the Indian Ocean that was first announced in early 2009.

Source: Suite101. Insightful writers. Informed readers.

Abstract:

In the tropical Indian Ocean, the Maldive Islands lack surface freshwater, so are unsuitable for dragonfly reproduction. Nevertheless, millions of dragonflies (Insecta, Odonata; mostly globe skimmer, Pantala flavescens) appear suddenly every year starting in October. Arrival dates in the Maldives and India demonstrate that the dragonflies travel from southern India, a distance of some 500–1000 km. Dates of arrival and occurrence coincide with the southward passage of the Inter-tropical Convergence Zone (ITCZ). Circumstantial evidence suggests that the dragonflies fly with north-easterly tail winds, within and behind the ITCZ, at altitudes over 1000 m. It is proposed that this massive movement of dragonflies is part of an annual migration across the western Indian Ocean from India to East Africa. Arrival dates in the Seychelles support this hypothesis. Dragonflies also appear (in smaller numbers) in the Maldives in May, with the onset of the southwest monsoon, suggesting a possible return migration from Africa. These proposed migrations of dragonflies, regularly crossing 3500 km or more of open ocean, were previously unknown. It is known that these dragonflies exploit ephemeral rain pools for reproduction; the monsoons and ITCZ bring not only alternating, seasonal rains to India and Africa, but also appropriate winds for dragonflies to follow those rains. Several bird species migrate from India across the western Indian Ocean to wintering grounds in Africa. They do so at the same time as the dragonflies, presumably taking advantage of the same seasonal tail winds. Many of these birds also eat dragonflies; the possible significance of this was not previously appreciated.

-------------------------------------------------------------------------------------------------------

• Do dragonflies migrate across the western Indian Ocean?


R. Charles Anderson (2009).


Journal of Tropical Ecology, Volume 25, Issue 04, July 2009 pp 347-358 http://journals.cambridge.org/action/displayAbstract?aid=5645072


Image source: Flickr