Tuesday, August 23, 2016

The dragonfly that wanders the globe

            It’s not often that a common dragonfly makes the international news, but the wandering glider did just that in March. The two-inch long insect generated the attention for its remarkable long distance flying abilities. According to research by a Rutgers University biologist and her student, wandering gliders frequently make transcontinental migrations. Hundreds of thousands of them have been seen crossing the Indian Ocean from Asia to Africa, for instance, and they have been observed on every continent except Antarctica, making them the most widespread dragonfly on Earth.
            In New England, wandering gliders are quite distinctive as one of the very few dragonflies that appear orange in color as they dart by at eye level.  That appearance is somewhat deceiving, though. In the hand, they usually appear more yellow than orange. But their large red eyes and orange stigma – a spot on the leading edge of the wings, near the wingtip – combine with their golden yellow bodies and an amber wash on their clear wings to make them look orange.
Wandering Glider by Greg Lasley
Females typically lay a clutch of 500 to 2,000 eggs in vernal pools and other temporary puddles by tapping their abdomen on the surface of the water. (Biologists say it’s not unusual for the insects to attempt to lay their eggs on the shiny hoods and roofs of vehicles that they mistake for puddles.) But they are most often seen from July through September cruising back and forth over meadows, power line corridors and other openings while hunting for insects, which they capture and consume on the wing. Large swarms of wandering gliders can sometimes be seen feeding together when food is abundant, though you can often get the best view of them when they perch vertically on vegetation, usually close to the ground.
It’s in the fall when they migrate south that their name is most apt, however. Unlike most dragonfly larvae, which overwinter in the pond or stream in which they hatch, wandering glider larvae develop in less than two months, allowing them to emerge from the water in late summer or early fall and transform into their adult stage. They then undertake the epic migration that can take them out over the ocean for days or weeks at a time, feeding as they go on aerial plankton. This feat means they surpass the monarch butterfly as the insect with the longest migration, putting them on par with many whales and birds.
Since wandering gliders – sometimes called globe skimmers – are too tiny for researchers to use GPS technology to track their movements, scientists analyzed the genes of specimens from far flung locations around the world to learn how widely they travel. This information served as a proxy for how often dragonflies from widespread locations mate with each other. They apparently do so quite regularly; so often, in fact, that their global gene pool is largely homogenous.
Lead researcher Jessica Ware told Newsweek that most species have a “neighborhood effect” in which individuals that breed in the same vicinity tend to be more closely related genetically than those living farther away. But that’s not true of the wandering glider. “Because the entire world is their neighborhood, any [wandering glider you see] is likely to be as closely related to one in Europe as it is to one in South America,” she said.
The insects are well adapted for their intercontinental travels. Their wings are long and broad and built for gliding – somewhat like albatrosses, which also soar across the oceans – and they are considered the highest flying dragonfly after having been recorded flying more than three miles above the surface of the Earth. This means they can take advantage of oceanic winds to carry them much of the way to their ultimate destination without having to flap continuously.
But it’s not an easy trip. Ware calls it “a kind of suicide mission,” since many die along the way. Those that make it, however, help to assure the survival of the species, since their long migrations are believed to be part of a strategy that provides that at least some will end up somewhere with available freshwater to breed in, regardless of the season.

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