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Blue Whales are the largest animals ever known to have lived on Earth, growing up to 100 feet long and weighing as much as 200 tons. They are a type of baleen whale, which means they have a comb-like structure in their mouths instead of teeth that they use to filter krill, their main food source, from the water. Blue Whales are found throughout the world's oceans and can be seen migrating to warmer waters during the winter months. They are known for their distinctive calls, which can be heard for miles and play an important role in their communication and mating behaviors. Despite being a protected species, Blue Whales still face threats from pollution, ship strikes, and climate change. As a subcategory of Whales, they are a part of the Marine Reptiles category within the broader Marine Life category, all of which fall under the Animals top-level category.