Substrate feeders are animals that live in or on their food source and actually move by eating their way through the food.

Imagine for a moment that you lived in a giant tank of jell-o, and the only way you could move from point a to point b would be to eat through the lime green goodness. You'd be a substrate feeder!

Substrate feeders include caterpillars, which eat their way through leafy greens, leaving a trail of feces behind them. Another popular substrate feeder is the earthworm. They eat their way through the earth, digesting organic materials to fertilize and aerate the soil.