Live fast, travel far, and mate randomly wherever the wind blows you is the life strategy of the globe skimmer dragonfly. Found on many continents in wide-spread locations, globe skimmers are difficult to track directly because they are too small to wear radio transmitters and have thin wings that can’t be tagged. So instead of mapping migration routes, scientists examined genetic make-up to evaluate the likelihood of a globe skimmer dragonfly from North America breeding with one from Japan. The answer reported in a study published last week* establishes a new world record for insect migration.
Globe skimmers (Pantala flavescens, also called wandering gliders) are one world-wide population from the same gene pool. They circumnavigate the globe and migrate from continent to continent. Although monarch butterflies were thought to be the champions of insect migration at 2,500 to 3,100 miles, these dragonflies have them beat with distances of 4,400 miles. They are the only insect known to migrate across oceans. Globe skimmers are panmictic, meaning they mate randomly all over the world. Panmictic breeding is rare among animals (presumably excluding humans), occurring mostly in ocean species like sea coral, European eel, and some fish.
Entomology Today
Biologists at Rutgers University found that populations of this dragonfly in locations as far apart as Texas, eastern Canada, Japan, Korea, India, and South America, have genetic profiles so similar that there is only one likely explanation. Apparently, these insects are traveling extraordinarily long distances, and they are breeding with each other, creating a common worldwide gene pool that would be impossible if they did not intermingle.
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Globe skimmer migration follows favorable weather. Requiring fresh water for mating and egg laying, they ride the winds in search of good weather. For example, determined dragonflies annually leave India in dry season to visit Africa during rainy season. The larvae have a short development time (38-65 days) and can mature quickly to fly off and continue migrating before ephemeral pools dry up.
...if while riding a weather current they spot a fresh water pool created by a rainstorm, it’s likely that they dive earthward and use those pools to mate. After the eggs hatch and the babies are mature enough to fly, which takes just a few weeks, the new dragonflies join the swarm’s intercontinental and now multi-generational trek right where their parents left off.
Designed for long distance travel with a large wing surface area, their broad hindwing supports gliding, helping them travel extraordinary distances by riding on currents without expending much energy. This puts the global skimmer at the mercy of wind currents and results in them being blown off course to remote locations. One such location is Easter Island where the global skimmer population became resident and developed body and behavioral traits that favor non-migration.
...they crouch low against the substrate rather than lift their tarsae [last segment of their legs] when wind passes over their wings and possess smaller hindwings than continental populations.
The one and half inch long globe skimmer takes suicidal risks to find clement weather. While many die during migration, enough survive to continue the trip and support a global population. Some of the other 6,000 dragonfly species live, breed, and die in the same pond without straying more than 36 feet from home. A few species (25-50) migrate regionally, such as the common green darner (Anax junius) who summers in the U.S. and migrates to Texas and Mexico. But no insect travels further than the globe skimmer and has as much random sex along the way.
DRAGONFLIES ACTIVE NEAR YOU YET THIS SEASON? WHO’S BLOOMING? GOT MOTHS?
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* Original research published by PLOS ONE: A Global Population Genetic Study of Pantala flavescens