Fig. 3

a Illustration of the setup and measurements. A QPD is monitoring an air volume through a telescope. The FOV is terminated in a black cavity to reduce the optical background. When an insect transits the FOV, sunlight is scattered into the telescope and recorded by the sensor. The QPD is sampled continuously with a DAQ board, and the signal is stored in a computer. b Map of the measurement site at Stensoffa in Southern Sweden (N55.70, E13.45). The telescope is aimed into a black cavity located 142.3 m away in a roughly northwards direction