Washington (Online): A group of British scientists have measured the migration of insects in the skies and found that more than three trillion passes over our heads each year.

According to the scientists, Insects play a key role in healthy ecosystems. They pollinate crops, eat crop pests and provide food for birds and bats.

Experts say this first-of-its-kind measurement suggests insect migration, which most of us never see, is a major event.

Co-author Jason Chapman of the Centre for Ecology and Conservation at the University of Exeter's Penryn Campus in Cornwall said, "Insect bodies are rich in nutrients and the importance of these movements is underappreciated."

"If the densities observed over the 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."

The study published in the journal Science stated that such movement would take up 3,200 tonnes by weight, more than seven times the mass of the 30 million songbirds which leave Britain for Africa each autumn.

Most of the travelling, some 70 percent is done by day, said scientists at the University of Exeter and Rothamsted Research.

Using special radars pointed at the sky, lead author Gao Hu tracked the migration of insects at a height of 150 meters (yards) for nearly a decade.

The annual average came out to 3.37 trillion insects .

The researchers said that the travel was heaviest on warm days.