D. mexicanus, and indeed most fossorial caecilians, are “sit and wait” predators. When they approach prey, they do so very slowly, and they do not pursue fleeing prey. They capture prey with their powerful jaws. Most caecilian prey is elongate, and is thinner than the caecilian itself. Earthworms are a very common prey item, and there is a population in Guatemala found to feed exclusively on earthworms.
Normally, D. mexicanus and most other caecilians feed via a static pressure system. The animal captures and crushes prey with its powerful jaw, and then swallows the prey whole. Ingestion is a fairly continuous process alternating between biting and swallowing motions. However, when capturing prey while partially emerged from its burrow, D. mexicanus has been observed spinning back into the burrow in a corkscrew, and shearing the prey against the sides of the burrow.