Strictly speaking, ostriches are not carnivores because they do not only eat meat, nor are they herbivores because they do not stick to a plant based diet only. Ostriches are considered omnivorous creatures and basically eat anything they come across as well as the things that many other animals are unable to digest. They mainly feed on plant based materials such as grass, seeds, fruits, and leaves from trees and bushes. However every now and then they do enjoy eating small vertebrates such as lizards, frogs and birds and invertebrates such as insects including locusts, grasshoppers and worms.
Interestingly enough, ostriches do not have teeth and often swallow pebbles or sand to help with food digestion in the gizzard. Food collects in the crop and then slides down the neck in a bolus. The ostrich has intestines that are 14 meters long which helps it get the most out of the tough plant based food sources it eats. These interesting creatures are able to go without water for several days due to the fact that they can survive on the moisture from plants instead. They also are capable of making their own water internally.