Masters of the monsoon

So, at altitudes above 1,000 m, the dragonfl ies could be able to reach the Maldives using these winds. Studies in China have found the dragonfl ies fl ying at these heights and studies of air pollutants have shown that they can spread from southern India to the Maldives at speeds of 10 m per second. With such tailwinds, dragonfl ies might make the crossing from India to Male in 24 hours or less. But Anderson believes the dragonfl ies’ arrival in the Maldives represents a short break in a journey to east Africa and he has gathered considerable circumstantial evidence to back his claim. Large numbers of dragonfl ies start appearing in the northern Seychelles, 2,700 km from India, in November, and then in Aldabra, 3,800 km from India in December. Dragonfl ies appear in Tanzania and Mozambique in December and January. These dates strongly suggest that the dragonfl ies take advantage of the moving weather systems and monsoon rains to complete an epic migration, says Anderson. These dragonfl ies exploit temporary pools of water where predators are absent but prey, such as mosquito larvae, are present and they can complete their larval life in as little as 40 days, which is remarkably quick compared with most dragonfl y species exploiting longer-lasting pools. He believes the dragonfl ies are then able to exploit the northward movement at the back of the ITCZ in the following spring to migrate back to India, arriving in the Maldives on their way in May and June. This would amount to an epic roundtrip migration of 14,000–18,000 km involving four or fi ve generations of dragonfl y. He also points out that this proposed migration is similar to that known to be taken by several insect-eating birds, including cuckoos, nightjars, falcons and bee-eaters. The proposed dragonfl y migration suggests that the birds might feed on the insects during their migration. The proposed dragonfl y migration exceeds even that of the Monarch butterfl y, which, over four generations, completes a 7,000 km migration from Mexico to Canada and back. Anderson acknowledges the uncertainties in his hypotheses but the possibility that these insects are making a regular seasonal transoceanic migration “should excite further interest in these extraordinary animals,” he says.