Dragonflies likely migrate across the Indian Ocean

In 2009, marine biologist Charles Anderson put forward a hypothesis after observing globe skimmer dragonflies(Pantala flavescens) on the Maldives, that had flown in from what he assumed was India. When they flew off again, it was towards East Africa. Now, 12 years later, a group of researchers decided to investigate his claim.

Globe skimmer dragonflies are too small to be fitted with transmitters. Instead, the researchers examined its physiological aspects and calculated how long a globe skimmer dragonfly could stay airborne using the energy that can be stored in its body. In addition, the researchers used meteorological wind models to determine if there are winds that can facilitate the migration in both directions.

"Our study shows that this migration from India to East Africa is actually possible. However, the globe skimmer dragonfly can't manage it using only the fat it can store in its body. It also requires favourable winds and these are present during certain periods of the year," says Johanna Hedlund, a biology researcher at Lund University.

According to the simulated migration experiments using wind models, about 15 per cent of the dragonflies could manage the migration from India to Africa in the spring. In the autumn, 40 per cent could make the same journey in the opposite direction.

Johanna Hedlund and her colleagues consider it impressive that dragonflies can do this at all. Even more impressive is the fact that the globe skimmer dragonfly migration across the Indian Ocean is the longest in the animal kingdom in relation to an animal's size.

"We have got a lot closer to solving the mystery of how a tiny dragonfly, which only weighs 300 milligrams, can cross 2,000 kilometres of open sea," says Johanna Hedlund.

Other animals also rely on favourable wind conditions when they migrate. Two examples are the amur falcon and the Jacobin cuckoo, which also fly across the Indian Ocean. The researchers behind the study in question warn that climate change may affect the chances of these birds and the globe skimmer dragonfly in the future. There is a risk that wind patterns will change when the water surface gets warmer.

The researchers consider that the study is important in several ways. It creates an understanding of the distances that one of the animal kingdom's smallest migrants can cover, it increases knowledge about how migratory animals can spread diseases, and it also contributes to ecosystem services at widespread locations around the world.