Researchers Record Trillions of Migrating Insects Swarming Through the Skies

Though bugs make up a large amount of biomass, little was known about their migrating habits, until now

A painted lady butterfly, Vanessa cardui, one of thousands of insect species that migrate over southern England University of Exeter/S.R.Miller/Fotolia

Songbirds do it. African wildebeests do it. Even whales and many species of fish do it. No, we're not talking reproduction (though they do that, too). Every year, all these creatures undertake an epic migration. But the seasonal journeys of one class of living creatures has long gone overlooked: insects. 

Now after a decade of monitoring, researchers have tallied the bugs that undertake this massive journey. Their results, recently published in the journal Sciencesuggest that some 3.5 trillion insects (which translates to 3,200 tons of biomass) migrate over southern England each year—a scene that likely takes place around the world, reports Nell Greenfieldboyce for NPR.

The researchers monitored insects passing above 500 feet in the air, according to a press release. To count the winged invertebrates, they pointed a narrow beam radar directly into the sky, which detected insects slightly larger than a housefly, reports Deborah Netburn at the LA Times. But to count the waves of smaller insects, they sent up nets attached to small helium balloons to collect snapshots of the migration.

“Insect bodies are rich in nutrients and the importance of these movements is underappreciated,” lead author Jason Chapman of the Centre for Ecology and Conservation at the University of Exeter in England, says in the release. “If the densities observed over southern UK are extrapolated to the airspace above all continental landmasses, high-altitude insect migration represents the most important annual animal movement in ecosystems on land, comparable to the most significant oceanic migrations.”

Like songbirds, the researchers found that huge masses of insects move northward in the spring and southward in the fall. Some species, including butterflies, even cross the English Channel for migratory trips as far as Africa. Netburn reports that unlike birds, about 70 percent of the insect migration takes place during daylight hours.

In fact, Chapman tells Greenfieldboyce that insect numbers in southern England are probably not indicative of the rest of world because the area is relatively cold and damp. “I believe the numbers in the southern UK are close to minimum values for the rest of the world,” Chapman tells Netburn. “Almost anywhere I can think of will likely have much higher values, especially in the hotter parts of the world.”

Hugh Dingle, a migration expert at the University of California Davis who was not part of the study, tells Greenfieldboyce that the work is impressive and that he isn’t surprised at all by the finding that insect migrations are so large. “It’s nice to see the data making this so apparent. Certain insects like locusts and the monarch butterfly, have gotten a great deal of attention. But perhaps because of all that attention on these big charismatic insects, the huge migrations that occur in lots and lots of other insects, all the way down to tiny aphids, are certainly not as well known by the public, and may not even be as well known by scientists.”

Netburn reports that Chapman and his team have begun similar work on insect migrations in Texas, and they are already overwhelmed by the sheer number of invertebrate they are finding that migrate through the skies of the Lone Star State.

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