Maggots consume dead or decaying organisms so they are classified as a decomposer.
Decomposition is a process by which organic substances, like leaves or dead animals, are broken down into simpler matter.
A lot of different types of organisms, called the decomposers, will consume the organic substances and continue an essential part of the nutrient cycle. These organisms can be both bacteria, fungi but can also be insects.
This is important for recycling the organic matter that occupies space in the biosphere and that way, continues the movement of energy and matter in ecosystems.