Mosquitos, why do we need them?

Mosquitos, the only creature that I feel that are the only creature that won't effect any ecosystem in a bad way if they just ceased to exist. Think about it from my point of view. The only thing that I think that they actually do is that they are eaten by other critters, like spiders, but spiders have more things to eat, like flies, another pointless bug, I mean there life expectancy is only a couple day, but I was talking about mosquitios. Besides being food for other critters I think that they pretty much buzz around, being a nuisance and taking blood. They don't even take enough for it to matter, so why do we have those creatures.