Pine beetles did not escape from danger before the fire broke out, but targeted to find the place where forest fires raged. Female pine beetles like to lay eggs in charred trees. Since most insects don't patronize charred trees, the beetle eggs won't be harmed. When the larvae grow up, they will move to the phloem of the charred trunk, where there is enough food for them to enjoy. Two sensory organs on the side of the pine beetle's abdomen enable it to feel the fire source and fly to the fire area. They are particularly sensitive to infrared rays. The sensory organs of pine beetles consist of about 70 sensory cells, and each sensory cell consists of a tiny hard epidermal sphere. The watch ball absorbs the thermal radiation with the wavelength of 3 microns very well, which is about equivalent to the radiation generated by forest fires. In the process of absorption, the balloon on the surface will heat up, expand and stimulate the receptor. Pine beetles can use this wavelength of radiation to identify fire sources dozens of kilometers away. Using this bionic principle, German scientists developed a fire alarm.