Step outside and imagine there's a blanket of billions of insects overhead—because there probably is. Researchers who spent a decade tracking insects 500 to 4,000 feet above the ground in south-central England using radar beams and nets found about 3.5 trillion bugs and butterflies migrate across the region each year—moving south in the fall and north in the spring, much like birds. To picture it another way: Their mass is equal to about 20,000 airborne reindeer, reports the BBC. An ecologist says the number is "stunning," per Science, and another wonders how many more fly "over the basins of the Amazon or the Congo?" Indeed, "if you were to repeat this study almost anywhere else, I guarantee that you would exceed those numbers," study author Jason Chapman tells NPR, citing England's cold and wet conditions.
While small insects weren't picky about wind direction, scientists were surprised to find that larger insects appeared to be more deliberate in choosing whether to fly given current wind direction. "It signifies that the insects have a compass mechanism in order to know which is north and south, but they also have the capability to then fly up high into the sky and assess the direction of the wind," compare the two, and decide what to do, which is "quite complex," Chapman says. The researchers also noted that the bugs weren't exactly leisurely flitting above. Some take advantage of fast-moving air currents to travel distances of up to 200 miles at speeds of up to 36 miles per hour. (Meet the world's longest-distance flier.)