What's a wasp's purpose?

Question

do they pollinate plants? are they predators?

Answer 1

they do pollinate plants, and they are also predators, most of them have formed a symbiotic relationship/covolution with some flower species.

Their purpose however is questionable, you may as well ask the big one, like what is the purpose of humans?

Answer 2

God gave wasps to demonstrate sin. Adam and Eve's bad choice gave sin, so some bad things have no purpose, other than to remind us of sin.

Answer 3

I think you are really asking: "what is their niche in the ecosystem; what role do they play in the environment". Sammi did a good job of answering that.

As for the question you actually asked, lifeforms do not have a "purpose" other than their own survival and the survival of their species. They live to insure the existence of healthy genes in future generations.