ostriches mainly eat plant matter, but they also eat insects. the plant matter consists of seeds, shrubs, grass, fruits and flowers while the insects they eat include locusts. ostriches do not have teeth, and so cannot grind food as mammals do. instead, they swallow pebbles. an adult ostrich carries about 1 kilogram (2.2 lb) of stones in its gizzard, a special sac just before the stomach. the pebbles grind the food, and help its digestion. when eating, their gullet is filled with food. after that, the food is passed down their esophagus in the form of a ball called a bolus. the bolus may be as much as 210 ml (7.1 us fl oz). ostriches can live without drinking for several days.