How does a worm grind its food?
Because worms have no teeth, they have little capacity to grind their food. They are limited to food that is small enough to be drawn into the mouth. Usually this food is softened by moisture or by bacterial action. Bacteria, protozoa, and fungi undoubtedly help break down the ingested organic material. Every worm has one muscular gizzard, however, which functions similarly to gizzards in birds. Small grains of sand and mineral particles lodge in the gizzard. Muscular contractions in the gizzard wall compress these hard materials against each other and the food, mix it with some fluid, and grind all into smaller particles. One reason for manually spreading a handful of topsoil, rock dust, or lime into the worm bedding is to provide worms with small, hard particles for their gizzards.
