They do damage by random disruption, not directed cruelty. For this reason, many people do not like to attach the term evil to such occurrences. But one must admit that they are unfortunate and cause much suffering. Time s direction, and even existence, implies the increase in entropy, and thus the existence of natural evil. Only in the temporal, getig, world can the spiritual, menog, conflict be played out.
Human evil is less problematic.
Zarathushtra continually rails against the violence and cruelty he sees around him. He calls upon people to choose righteousness. But few people willfully choose to be evil. They simply fail to exercise their good minds to choose good. Human evil is also basically a disordered condition, a failure of the moral faculty, not an active seeking of the wrong.