The list is long, in part because there are many kinds of barrel cactus. In short, many insects, including bees, flies, beetles, moths, and butterflies, serve as pollinators and depend on the nectar and pollen. Ants and other insects eat nectar produced by extrafloral nectaries. Chuckwallas sometimes eat the flowers. The fruits are eaten (and the seeds dispersed) by mule deer, peccaries, and many kinds of birds; the winter diet of mule deer may be as much as 42% barrel cactus fruits! Rabbits often eat barrel cacti if the spines are removed, for example by fire. Occasionally, woodpeckers will build nest cavities in barrel cacti, if they're tall enough, and other birds such as elf owls use these cavities later on.