Millions of dragonflies are flying thousands of miles from India to Africa in the insect world’s longest migration, scientists say.

If the new claim is confirmed, it would be the first mass journey by insects across the open ocean and would outstrip the famous 4,300-mile monarch butterfly migration from Mexico to Canada.

The 11,000-mile Indian Ocean migration is why millions of dragonflies appear every year in the Maldives as if from nowhere, according to research published this week.

The annual event is mystifying because the chain of islands lies between 300 and 600 miles from mainland India and has no fresh water – essential to the dragonflies’ life cycle.

Biologist Charles Anderson, based in the Maldives, said: ‘No one I have spoken to knew where they came from.’

He has amassed observations since 1996 from the islands, from the mainland and from ships at sea and says they reveal a migration from southern India which arrives in Maldives capital Male about October 21.

‘That by itself is fairly amazing, as it involves a journey of 600 to 800km across the ocean,’ says Mr Anderson.

He believes they fly at heights of at least 3,200 feet because lower down the winds blow in the wrong direction.

The dragonflies – mostly a species called globe skimmers (Pantala flavescens) – appear in surges until December but each surge only stays a few days.

Dragonflies then appear in the Seychelles – between 1,700 and 2,400 miles from India – in November and December.

Mr Anderson adds: ‘I have also deduced that they are flying all the way across the western Indian Ocean to East Africa.’

Globe skimmers appear in Tanzania and Mozambique in December and January.

In April the dragonflies reappear in the Maldives – which suggests the insects are making a round trip of up to 11,000 miles.

‘The species involved breeds in temporary rainwater pools. So it is following the rains, taking sequential advantage of the monsoon rains of India, the short rains of East Africa, the summer rains of southern Africa, the long rains of East Africa, and then back to India for the next monsoon,’ Mr Anderson told BBC Earth.

‘It may seem remarkable that such a massive migration has gone unnoticed until now. But this just illustrates how little we still know about the natural world.’