Trillions of Migrating Insects Take to the Sky Every Year

And that’s just over one part of England.

A Gulf Fritillary butterfly in flight. (Wikipedia user: Umbris.)
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Remember the horror film The Swarm, in which a bunch of killer bees go on a rampage, destroying a military base and crashing helicopters? Or Them!, in which giant, irradiated ants attempt to take over Los Angeles? Well, insects may not be as organized as that, but a new study shows that an astonishing number of bugs participate in coordinated seasonal migrations.

Each year, trillions of ladybugs, dragonflies, moths, and other insects migrate in a purposeful manner—not randomly. Gao Hu, of Nanjing Agricultural University, and his colleagues spent a decade tracking and quantifying insect flight in three areas of England, and published their findings in this week’s Science.

Using data collected by upward-pointing radar beams and aerial samples of bugs captured by nets hung from blimps, the team was able to track the size, speed, and direction of various insects. They made some surprising discoveries: Insects migrate north and south in seasonal patterns, just like birds. Insects completed a spring migration, traveling north in May and June, before spending July riding the winds in an aimless manner. (Ah, summer.) During August and September they once again headed south.

Researchers focused on insects flying 500 to 4,000 feet above ground level; smaller, lower-flying insects don’t make long-range seasonal migrations, note the authors, and were excluded from the study. And it’s generally too cold in the UK for insects to fly above 4,000 feet. The scientists also discovered that insects didn’t just move with prevailing winds; they actively selected winds that corresponded with their preferred direction.  

If the huge numbers observed over the UK (3.37 trillion insects, making up 3,200 tons of biomass) are applicable to the airspace above all landmasses, say the authors, high-altitude insect migration “represents the most important annual animal movement in terrestrial ecosystems, comparable to the most significant oceanic migrations.”

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