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Last Updated: Wednesday, 10 May 2006, 19:02 GMT 20:02 UK
Tiny tags trace dragonfly paths
A transmitter is attached to a dragonfly's thorax ( C.Ziegler)

The epic journeys taken by dragonflies searching for warmer climates have been revealed by scientists in the US.

The team, led by researchers from Princeton University, found that the insects are capable of flying up to 85 miles (137 km) in a day.

Writing in the journal Biology Letters, the group describes how it tracked the movements by attaching tiny radio transmitters to the insects.

A scientific posse followed the signals from a receiving aeroplane.

Other researchers monitored the insects' progress from the ground.

Tricks of the trade

The dragonflies' route took them along the east coast of America towards the warmer south.

The data revealed that the dragonflies' migration patterns are strikingly similar to those of songbirds, suggesting there is a strong evolutionary link to their behaviours.

Dragonfly on finger ( Christian Ziegler)
The ocean prompts a change in direction ( Christian Ziegler)
"Insects have been around far longer than birds, therefore we suspect that they have been migrating far longer than birds," said Professor David Wilcove of Princeton University and one of the authors of the paper.

"It is just possible what we are seeing here are the basic primitive rules of migration and that birds converged on the tricks of the trade," he told Science In Action on the BBC World Service.

Billions of common green darner dragonflies (Anax junius) migrate every year but until now hardly anything was known about their routes or strategy.

The new research shows there is method behind the insects' flight behaviour.

For example, the dragonflies tended to only move after two nights of cooler temperatures, indicating a cold front was approaching with favourable north-westerly winds.

They also tended to change direction when they met a large body of water, ensuring they never became stranded out over the sea.

Two insects were recorded flying out over the ocean before reversing and skirting down the coastline.

The detailed flight path information was made possible by tiny radio transmitters developed by the team.

Final destination

Each transmitter weighed about a third of a gram and had enough battery life to track an individual for 10 days; but tagging such small creatures is far from easy.

"The challenge is first catching the dragonfly," said Professor Wilcove.

Once caught, each transmitter was attached with a couple of drops of superglue and some eye-lash adhesive.

However, the final destination of the green darners is still not known because of the power restraints of the transmitter set-up; and some individuals simply flew out of range of the scientists.

In the future, the team hopes to refine its techniques and make the tracking even more hi-tech.

"The dream scenario would be to get a satellite to pick up the signals from these transmitters," said Professor Wilcove.

"If you had a satellite like that you could [follow the migration of] all kinds of birds, dragonflies, and locusts; and, I think, it would shed tremendous light on the movements of these organisms."

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