Using the example of scale insects as evidence, why are natural predators important to an ecosystem

natural predators live and breed in their natural environment, where their prey can only be digested by a predator immune to an insects stings, poison, etc ... meaning predator & prey were from the same region. Important to an ecosystem because both specialize in preying on that type of insect, and the insect has specialized in getting away, or producing 10 x the offspring for best chance at survival ...