The emu (Dromaius novaehollandiae) is the largest bird native to Australia and the only extant member of the genus Dromaius. It is the second-largest extant bird in the world by height, after its ratite relative, the ostrich. There are three subspecies of emus in Australia. Emus cannot fly but they are fast runners - up to 48 km (30 mi) per hour - they are also strong swimmers. Some scientists consider emus to be living dinosaurs because their bones and joints are similar to dinosaurs. Their ability to store fat allows them to go without food for long periods of time. Emus can defend themselves with tremendously powerful forward kicks. They eat great quantities of caterpillars, grasshoppers, and masses of the burrs that tangle sheep wool, which makes them helpful to farmers.