system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What makes flies important to the ecosystem?
gpt
They're part of the nature. They seek out decomposing flesh and lay their eggs on it, and their larvae eat it and help to break down the rotting flesh in to more basic components that can be absorbed in to soil to fertilize it for vegetation. They also aid in pollination of certain plants. They're also a key part of the food chain for lots of other creatures.

They may seem like a pest but they're integral to the natural balance of the world and without them lots of other animals like birds, lizards, toads, and a bunch of other species that don't come to mind right now would have a harder time surviving; and when their population dwindles, so does lots of other species. The natural food chain is a delicately balanced thing, and any disruption to it can have rippling effects.