PURPOSELESS DESTRUCTION (Bal Tashchit)

Bal Tashchit May Override Custom
You may not destroy things in the world for no purpose. You may not waste anything (bal tashchit) that has a use, but you may use it for a purpose. Bal tashchit overrides customs and suggestions of what are good behaviors or actions.
ExampleIf you kept food under your bed when you slept, although there is a problem with ru'ach ra'a, you should eat the food, give the food to a non-Jew, or somehow use the food, but not throw it away.

 
Killing Creatures that Harm
You may kill any animal, bird, or other living creature that bothers, injures, or endangers people or destroys property (as long as it is legal by the laws of the local country or area). This includes animals that eat your food or produce.