Here's why:
* Size: Blue whales can grow up to 100 feet (30 meters) long and weigh up to 200 tons (400,000 pounds). That's longer than a Boeing 737 airplane and heavier than 30 elephants!
* Habitat: They live in all oceans around the world, but prefer warmer waters.
* Diet: Blue whales are filter feeders, meaning they eat tiny animals called krill.
While some might argue that the giant squid is larger, we have only ever seen them in dead specimens, and their size estimates are based on limited data. The blue whale, on the other hand, has been extensively studied and is the largest animal on Earth, land or sea.