Step 1: Understanding the Concept:
The question asks for the specific term for the physical breakdown of dead organic matter (detritus) by detritivores like earthworms. This is a key step in the process of decomposition.
Step 3: Detailed Explanation:
The process of decomposition involves several steps:
\[\begin{array}{rl} \bullet & \text{Fragmentation: This is the first step where detritivores (like earthworms, termites) break down detritus into smaller particles. This action increases the surface area for microbial action.} \\ \bullet & \text{Leaching: Water-soluble inorganic nutrients seep down into the soil horizon and get precipitated as unavailable salts.} \\ \bullet & \text{Catabolism: This is the enzymatic process where bacteria and fungi degrade the simplified detritus into simpler inorganic substances.} \\ \bullet & \text{Humification: This step leads to the formation of a dark-colored, amorphous substance called humus, which is highly resistant to microbial action and decomposes at an extremely slow rate.} \\ \end{array}\]
Step 4: Final Answer:
The physical breakdown of detritus into smaller particles by earthworms is called fragmentation.