What is the primary material used to develop vermicompost?

The correct option is Earthworms.

Explanation:
Vermicompost is a high-quality organic fertilizer produced through the process of vermicomposting. The prefix "vermi-" is derived from the Latin word vermis, which means worm. In this process, specific species of earthworms (commonly red wigglers or Eisenia fetida) are used to consume and break down organic wastes such as vegetable scraps, agricultural residues, and animal manure. As the organic material passes through the digestive tract of the earthworms, it is decomposed and transformed into nutrient-rich worm castings (excreta). This finished product is known as vermicompost, making earthworms the primary biological agents responsible for its development.