Dragonfly migration reveals extraordinary global journeys

A dragonfly skims across a garden pond on a warm afternoon, vanishing almost as soon as it appears. Most people imagine that its life is limited to one pond and a short spell of summer.

That picture is largely mistaken. Some of these insects travel between continents and cross open oceans, undertaking journeys to rival those of migrating birds.

Scientists have only now established just how far the most extreme travellers go.

Dragonfly migration around the world

After examining nearly 400 studies, a research team has assembled the first worldwide picture of dragonfly and damselfly migration. Even those doing the counting were surprised by the result.

Across all the groups examined, only a small proportion were found to migrate – less than 2% of known species – while another 85 were considered probable migrants.

Dr Johanna Hedlund led the research at Lund University in Sweden and the University of Exeter in England.

She found that migration had probably evolved many times, emerging independently in several distinct lineages and being reinvented on each occasion.

Why some dragonflies leave home

Migration generally starts when conditions at home become unsuitable. The water in which these insects breed may become too cold in winter, or too hot and dry in summer.

Under those conditions, they cannot raise young and have little option but to leave.

Migratory species also follow a different timetable. An adult migratory dragonfly can spend months flying.

By contrast, relatives that stay put spend most of their lives underwater as nymphs, developing wings only late in life.

Long journeys leave their mark on the body as well. Migratory species generally have longer, smoother wings suited to gliding, allowing them to use moving air and flap less often.

One study documented that difference in wing shape along a migration route.

Crossing oceans on seasonal winds

Among the boldest travellers is the globe skimmer. At barely 5 cm long, it is thought to fly more than 2,400 km from north-eastern India to the Maldives, covering much of the distance over open sea.

The crossings are likely to depend on seasonal trade winds that blow in the right direction at the right time of year.

An analysis of the fuel needed for such a journey found that the insect can remain airborne for more than a week without landing.

At the destination, rain fills temporary puddles that do not last long enough for hungry fish to live in them. The next brood develops quickly, maturing in roughly 40 days.

Globe skimmers inhabit warm, wet places almost anywhere across Asia, Africa and the Americas. Their complete circuit, undertaken by successive generations, stretches over many thousands of kilometres.

Rare insects on solo journeys

Most insect migration works as a relay rather than a return trip: the individual that sets off seldom comes back.

Instead, its descendants complete the circuit started by their ancestors a generation or two earlier, making it a journey no single insect undertakes in full.

“That is rare in insects and, oddly enough, something research has not paid much attention to before,” said Hedlund.

A few dragonflies alone break that pattern, leaving and returning within a single lifetime. Researchers had missed the achievement until this worldwide assessment brought it to light.

Climbing to cooler ground

One kind of solo journey takes insects upwards rather than across the landscape. Known to scientists as altitudinal migration, it avoids heat by moving to cooler, higher ground instead of travelling across a map.

Japan’s red dragonfly, called the akiakane there, makes this journey every year.

Adults emerge in late spring and leave the hot valleys for cooler peaks. They come back to breed only when the air cools in autumn.

At that point, whole hillsides fill with them – a sight long treated as a seasonal curiosity rather than one of the rarest feats of endurance among insects.

Swarms and sustenance

The numbers involved can be as striking as the distances. A European dragonfly called the four-spotted chaser once swept across Belgium in swarms numbering hundreds of millions.

Migrating birds and bats still schedule their journeys to feed on such swarms.

Warming already appears to be changing some routes. The vagrant emperor, a North African dragonfly once uncommon in Europe, now breeds there and reaches as far north as the UK and Scandinavia.

This gradual movement north makes these insects what scientists call indicator species – living measures of a changing climate.

Their usefulness as trackers goes further. One study found very little genetic difference between globe skimmers from widely separated continents, as though the entire species were a vast family constantly on the move.

Following the movements of this one recognisable insect can begin to reveal the links between distant ecosystems.

It also provides a glimpse of the immense, unseen movement overhead of pollinators, crop pests and disease carriers.

What dragonfly migration reveals

What was once scattered speculation has become a clear map. Dragonfly migration occurs worldwide, with 100 confirmed species spread across several families.

A few achieve something almost no insect does: they complete an entire return journey in one lifetime. This makes them a rare scientific tool.

A group that is easy to spot can now serve as a proxy for the huge numbers of insects travelling across the planet, helping to improve efforts to track pollinators, crop pests and critical migration habitats.

In a few cases, the insect above a garden pond is also among the planet’s most extreme travellers.

With its full range now visible, that quiet flicker above the water becomes a signal scientists can follow and act on.