When monarch butterflies migrate, the world watches in wonder. Migrating birds also awe us, not least when we consider the vast distances they travel with their little wings. The migration of insects in general leaves us clammier. Yet, like many birds and four-legged animals, many insects migrate with the seasons, and the extent of invertebrate migration had never been measured until now, let alone its environmental impact. With climate change upon us, the time had come to look.
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An international team of scientists, working in the air space over 70,000 square kilometers of southern England for 10 years, discovered that relocating insects are the biggest movement of biomass on the planet. The diminutive winged creatures in question include ladybugs, aphids, locusts and butterflies.
About 3,200 tons of insects migrate over southern England each year on their way to Africa, report the scientists, including Dr. Nir Sapir from the University of Haifa. This is eight times more than the combined weights of all birds and bats migrating over the region annually, they estimate in an article entitled “Mass seasonal bioflows of high-flying insect migrants,” in the December issue of Science.
Put otherwise, 3,200 tons of bugs is equivalent to 10 Boeing 777s.
How many bugs is 3,200 tons? About 3.4 trillion, give or take a few million. And of these masses, some 70 percent migrate during the daytime and the rest are nocturnal, the researchers observe.
Apropos monarchs, about 150 million of them, weighing an aggregate 75 tons, fly between North America and Mexico each year.
Radars for high-fliers
People tend not to notice migrating insects, partly because many fly at high altitudes. The team studied insects migrating at heights of between 150 to 2,000 meters, using specialized radar techniques: Insects, they explain, are too small to carry transmitters or to be observed by any other means. Netting also proves helpful.
Impact there must be. Massive amounts of nutrients locked in those tiny little bodies are moving between continents. Also, insects are a crucial part of human endeavor, ranging from farming to lipstick manufacture. Change in their patterns portends change in the way we live.
However, what the enormous movement of insects through the planet’s skies means for ecology has yet to be elucidated. Since springtime movement north and autumn movement south roughly cancel each other out, over the long run, there should be no net ecological effect from that perspective. But the fluctuations can be vast, as much as 200 tons of insects in either direction in any given year, and this should affect annual exchanges of energy and nutrients.
On a final intriguing note, the scientists proposed that larger insects have in-built compasses. “If high-flying insects have a compass sense, one would predict that, in addition to selecting a favorable tailwind, they would also orientate in the seasonally beneficial direction and, thus, actively contribute to their wind-assisted displacement,” according to the team – which indeed witnessed that phenomenon.
Though the paper doesn’t dwell on the point, an urgent reason to evaluate the ecological impact of migrating insects is climate change. Global warming has already been playing havoc with the movement of larger animal populations, augmented by species permanently relocating. It is thus vital now to gain a better understanding of the environmental impact of insect migration, and how changes in it will affect us all.