Predators and parasites are those bugs that eat other bugs. Why are they important? It has to do with the way we grow our food crops and timber species in the most sustainable way. You see, all creatures on our planet belong to a web of life, or ecological system. We are all familiar with the following simple relationship: antelopes eat grass and lions eat the antelopes. In other words, there's always an animal that eats another animal.
If we make it a bit more complicated, we can add the fact that most — if not all — antelopes have internal parasites (roundworms, tapeworms and tiny, thin flukes that feed on the host) and some of these parasites can be transmitted to the lion as it eats the freshly-killed prey.
In our gardens, orchards, wheat fields, vegetable plots and forests, similar relationships exist between pest bugs (that damage our crops) and their predators. All we need to do is keep our predators and parasites happy and they will provide us with a pest-control service that is not only targeted at our plant pests, but is also sustainable and leaves no chemical residues on our food crops.
It is literally making use of the most finely tuned ecological relationship between plant pests and their natural enemies, and they do it for free!