Ostriches are considered omnivores. They eat everything from small vertebrates such as birds, lizards, and frogs to invertebrates such as grasshoppers, locusts, and worms. They also eat plant-based materials such as fruit, seeds, grass, and leaves from the trees and bushes. They also eat foods that most other animals don't eat.
Ostriches do not possess teeth and often swallow grains of sand and pebbles to assist in the digestion process in the gizzard. They can go without water for several days because they can depend on moisture from the plants instead. They are also capable of producing their water internally.
No, they are not carnivores; they are omnivores. They can feed on both plants and animals. They like to eat more plants than animals. The only set of animals they like the most are insects. They hunt for insects by putting their heads into the ground in a bid to get more insects to eat. They are able to eat both plants and animals because their digestive system supports it. They have three different stomachs and a very long intestine.
The nature of their digestive system is the reason why it takes a lot of hours for their food to digest. They don't have any teeth, which means they won't be able to grind whatever they eat until it gets to their stomachs. What they usually do to overcome this limitation is to eat sands and pebbles. The sands and the pebbles are what they will use to grind the food which they have eaten.