The blue whale feeds on small organisms called copepods and krill. It eats by sucking in a mouthful of water and krill and then filtering out the water through its baleen bristle teeth.
The blue whale is the largest mammal on the planet, weighing in at 150 tons. Krill, on the other hand, typically grow to less than an inch, although the largest can reach 6 inches. In order for a blue whale to live on a diet of krill, it needs to eat up to 8,000 pounds of krill a day, which equals about 40 million individual krill. Newborn blue whales live on their mother's milk for their first 18 months of life, with the mother supplying almost 150 gallons a day.
A blue whale eats by filter feeding, which involves diving into a school of krill with its mouth open and taking in a large amount of krill and water. It then closes its mouth. The whale's teeth are made of brush-like bristles with only enough room between them to filter out water. It pushes the water out using its tongue and then swallows the krill. On occasion, the blue whale also sucks in other food such as fish or crustaceans.