I'm gonna be different and say spiders.

Spiders are said to eat the mass of the entire human species every year. That's mostly insects. And that's an enormous amount to hand the insect population swell by every year. Of course, it would only increase that much in the first year. After that the growth would probably be exponential, at least until food sources were eliminated. Then the species that depend on those would go the same way, and so on up the food chain. It would probably actually be quite fascinating to see from an external perspective, or to study after the fact.