Crouching scientist hidden dragonfly: monitoring insect lifestyles in the air and the mud

Science News,  August 12, 2006  by Susan Milius

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When Martin Wikelski and David Wilcove went bird-watching in Cape May, N.J., one fall day in 2004, they were surprised to find that the main spectacle had four wings instead of two. Migrating dragonflies filled the air, flashing iridescent green and blue as they hovered over dunes, perched, then zipped off.

"They were everywhere," says Wikelski, who's a biologist at Princeton University. He and his Princeton colleague Wilcove had come to admire birds that take a break on the long haul up and down the East Coast, but insects on long journeys need rest stops too.

Wikelski has studied bird migration and pioneered the tracking of individuals on long flights. He says that as he and Wilcove marveled at the dragonfly air show along the New Jersey coast, they thought, why not track them too?

The scientists knew the difficulties that they were likely to face. Even the newest, lightest tracking devices might weigh down the insects so much that they couldn't get off the ground. Or the dragonflies might simply refuse to keep migrating after a scientist had glued baggage onto them.

"We knew people would think this was a crazy idea," Wikelski says.

He and his colleagues have now published an account of their efforts. It's one of several recent works exploring hard-to-see aspects of dragonfly life.

Although dragonflies are among the most familiar of insects, science is just beginning to unravel their complex life stories, which start in water and end in air. That cycle sends dragonflies into clashes and coalitions with an unusually wide range of other creatures.

Beyond the satisfaction in discovering details of the lives of charismatic animals, the new approaches to dragonfly ecology have implications for conserving these creatures and the wetlands they rule.

WHAT'S UP? Migration biologists have spent decades tracking animals en masse. Wikelski contends that what's needed now is an individual bird's-eye view, or bug's-eye view, ofhow migration works.

The migrant dragonflies that Wikelski set about tracking were the common green darners (Anaxjunius), robust fliers with blue abdomens that turn purple as the temperature rises.

Of the 5,200 species of dragonflies and related damselflies in the world, scientists estimate that 25 to 50 make seasonal migrations. There's evidence for migrations among nine North American species.

These aren't migrations in the bird sense of the word. Each insect makes a one-way trip and another generation returns, scientists presume.

To follow single dragonflies, Wikelski decided on radio tracking.

He sought help from Jim Cochran of Sparrow Systems in Fisher, Ill., who built ultralight transmitters. "Each one of them is like a Stradivarius," says Wikelski.

To test a transmitter, which costs about $200, Wikelski and his colleagues fastened it on a female dragonfly's underside with a nontoxic glue--eyelash adhesive.

Wikelski recalls some nervous moments watching the dragonfly right herself on her perch. The transmitter may be light, but it's still about one-third the weight of a dragonfly itself.

Finally, the transmitter-bearing dragonfly took to the air--and stayed aloft. The team was exuberant. "It was like the launching of the space shuttle; everyone was jumping up and down," Wikelski says.

In all, the researchers attached transmitters to 14 dragonflies.

The researchers followed the insects from the ground as best they could with chase vehicles. At least twice a day, Wikelski got a better view by taking off in a small airplane to locate the insects.

The group followed the individual dragonflies for an average of 6 days, in which the insects covered about 60 kilometers.

On any given day, the insects either made one long flight of up to 6 hours or stayed in one area. "They behave like birds," says Wikelski.

They also stayed put on days when wind speeds topped 25 km per hour, even if the gusts would have swept them along their way.

In an upcoming Biology Letters, Wikelski's group describes radio tracking individual dragonflies. Now, the team is calling for a bigger effort, including a satellite dedicated to tracking small animals.

ELUSIVE LADLES Sophie Foster, now at the University of Toronto at Mississauga, has studied the Hine's emerald dragonfly (Somatochlora hineana) in Wisconsin. Although it doesn't migrate, there were plenty of questions about its movements. Such as where the females hang out when they're not mating.

In 1995, the federal government listed the Hine's emerald dragonfly as endangered. It survives in patches in the Midwest. Foster studied in Wisconsin's Door County in 2000. She worked with Daniel Soluk, who is now at the University of South Dakota in Vermillion.

The emerald dragonfly males patrol breeding grounds near spring-fed streams. For years, biologists have speculated on why there are so few females in many male territories.

Scientists have proposed various answers, such as die-offs of females or refuges for them in other locations. But Foster found no published tests of any of these ideas.