The largest animal on Earth is the blue whale (Balaenoptera musculus). These majestic marine mammals can reach lengths of up to 100 feet (30 meters) and can weigh as much as 200 tons (approximately 181 metric tonnes). Blue whales are known for their incredible size, making them not only the largest animals alive today but also the largest animals ever known to have existed on Earth. They primarily feed on tiny shrimp-like animals called krill, consuming up to 4 tons of krill each day during feeding season. Their immense size and unique blue-grey coloration make them a fascinating subject of study in marine biology.