Different species differ widely in their diets and may be carnivorous, herbivorous, or omnivorous. Members of some species eat honeydew from plants infested with aphids and certain other insects; others, called dairying ants, feed and protect the aphids and "milk" them by stroking. Harvester ants eat and store seeds; these sometimes sprout around the nest, leading to the erroneous belief that these ants cultivate their food. However, cultivation is practiced by certain ants that feed on fungi grown in the nest. Some of these, called leaf-cutter, or parasol, ants, carry large pieces of leaf to the nest, where the macerated leaf tissue is used as a growth medium for the fungus. Most leaf cutters are tropical, but the Texas leaf-cutting ant is a serious crop pest in North America. The army ants of the New World tropics and the driver ants of tropical Africa are carnivorous, nomadic species with no permanent nests. They travel like armies in long columns, overrunning and devouring animals that cannot flee their path; the African species even consume large mammals.