Decomposers are a basic and essential type of organism at the behest of what we call the food chain, because they are all those that deal with the use of matter and energy presented by the remains of animals and plants. Fungi and bacteria are the most prominent types of decomposers but we cannot ignore others such as slugs, worms and some insects.
Basically, they decompose the remains of the aforementioned organisms to transform them into inorganic matter. Putting it in other terms, we could say that they are those who deal with the recycling of nutrients, making that matter that passed from one to another can be used again by those who begin with the food chain, the producers, such as plants.
Decomposers absorb from these animal and plant wastes some products that serve them and will release at the same time as many that the abiotic environment, for example the soil, will incorporate and then be consumed by the producers. Then, the decomposers comply with the last part or link of the food chain and give way for the producers to start a new cycle.
In the specific case of insects, mosquito larvae feed on decaying matter during the winter and can lay their eggs in decaying matter.
For their part, bacteria are everywhere, in the air, on the ground or inside living beings, decomposing dead matter and recycling the carbon that plants will later use.
It should be noted that decomposers share existence in the ecosystem with two other types of living organisms, producers, who are responsible for transforming sunlight into energy through the photosynthesis process. And consumers who live thanks to the energy released by the former.