Insects fly high to survive.
As cold-blooded creatures, they rely on outside warmth to live. After the sun sets, the air temperature at higher altitudes is warmer than that nearest Earth because the ground cools faster then the air above it. An area of warmer air forms, known as the inversion layer. To stay within these warmer temperatures, insects climb higher with the rising inversion layer. At sunrise, the insects return to Earth as it becomes warm near the surface.