 Many snails are herbivorous, eating plants or rasping algae from surfaces with their radulae, though a few land species and many marine species are omnivores or predatory carnivores.Snails cannot absorb colored pigments when eating paper or cardboard so their feces are also colored.Several species of the genus "Achatina" and related genera are known as giant African land snails; some grow to from snout to tail, and weigh .