Prey includes a wide variety of small to medium-sized mammals and birds.[15] The bulk of their diet consists of rodents, but larger lizards and mammals as big as ocelots are also reported to have been consumed.[14] Young boa constrictors eat small mice, birds, bats, lizards, and amphibians. The size of the prey item increases as they get older and larger.
Boa constrictors are ambush predators, so often lie in wait for an appropriate prey to come along, when they attack. However, they have also been known to actively hunt, particularly in regions with a low concentration of suitable prey, and this behaviour generally occurs at night. The boa first strikes at the prey, grabbing it with its teeth; it then proceeds to constrict the prey until death before consuming it whole. Unconsciousness and death likely result from shutting off vital blood flow to the heart and brain, rather than suffocation as was previously believed; constriction can interfere with blood flow and overwhelm the prey's usual blood pressure and circulation.[16] This would lead to unconsciousness and death very quickly.[16] Their teeth also help force the animal down the throat while muscles then move it toward the stomach. It takes the snake about 4–6 days to fully digest the food, depending on the size of the prey and the local temperature. After this, the snake may not eat for a week to several months, due to its slow metabolism.