To decompose means to break down. Decomposers break down organic materials.
Decomposers consume anything that is dead. That includes other decomposers.
Some things that are decomposers are mushrooms, millipedes, potato bugs (sow bugs,) ect. A decomposer is a living object that helps break down dead organisms.
The Earth would be filled with the things that decomposers decompose.
Things that are not bacterium or fungi.