3.5T insects migrate across southern England each year

It’s one of the biggest mass migrations on Earth, and you probably don’t even know it happens.

Each year, from May to September, nearly 3.5 trillion insects traverse the skies above southern England, according to a new study in the journal Science.

Together these winged travelers make up 3,200 tons of biomass. That’s the mass equivalent of a herd of 800 fairly large elephants marching past the clouds.

And if you live in sunnier climes, like Southern California, the number and mass of insects flying over your head each year are likely to be even greater.

“I believe the numbers in the southern U.K. are close to minimum values for the rest of the world,” said study author Jason Chapman, an entomologist at the University of Exeter in Cornwall. “Almost anywhere I can think of will likely have much higher values, especially in the hotter parts of the world.”

Chapman and his colleagues say that if the densities they observed over southern England are indeed similar or larger over other parts of our planet, this insect migration could represent the most important annual animal movements on land.

Chapman has been studying various aspects of high-altitude windborne insect migration for 15 years, but for most of that time his focus has been on large nocturnal species — specifically, large moths.

In this study, however, he and his co-authors tallied migrating insects of all sizes, both day and night. All the insects in the study were flying at least 500 feet off the ground (a bit higher than a 30-story building).

To collect the data, the team used a special entomological radar that allowed them to determine body mass, flight altitude and a host of other information about individual insects with a mass of 10 milligrams or more (about the size of a housefly and bigger).

The radar cannot accurately measure the number of smaller insects, which are much more numerous than the larger traveling bugs. To solve that problem, the researchers used aerial netting to monitor the tiniest migrators.

The authors found that 99 percent of the individuals that migrated through the study area were in the smallest group of insects (those smaller than a housefly).