Transoceanic migration of dragonflies and branched optimal route networks

Abstract

The intriguing annual migration of the dragonfly species, Pantala flavescens was reported almost a century ago [1]. The multi-generational, transoceanic migration circuit spanning from India to Africa is an astonishing feat for an inches-long insect. Wind, precipitation, fuel, breeding, and life cycle affect the migration, yet understanding of their collective role in the migration remains elusive. We identify the transoceanic migration route by imposing a time constraint emerging from energetics on Djikstra's path-planning algorithm. Energetics calculations reveal a Pantala flavescens can endure 90 hours of steady flight at 4.5m/s. We incorporate active wind compensation in Djikstra's algorithm to compute the migration route from years 2002 to 2007. The prevailing winds play a pivotal role; a direct crossing of the Indian Ocean from Africa to India is feasible with the Somali Jet, whereas the return requires stopovers in Maldives and Seychelles. The migration timing, identified using monthly-successful trajectories, life cycle, and precipitation data, corroborates reported observations. Finally, our timely sighting in Cherrapunji, India (25.2N 91.7E) and a branched network hypothesis connect the likely origin of the migration in North-Eastern India with Pantala flavescens's arrival in South-Eastern India with the retreating monsoons; a clue to their extensive global dispersal.