The invention relates to wind energy systems. A wind energy system is provided having an insect sensor. The insect sensor is adapted for measuring the insect density in the air. Further, a method for operating a wind energy system taking into account the insect density in the air is provided. The wind energy system is curtailed during times with a high insect density. Hence, in periods following times with a high insect density, the wind energy system can be operated without the aero-dynamical performance of the rotor blades being spoiled by smashed insects.