The way to tell a shark from a cetacean is to look at its tail: cetaceans have horizontal tails, while sharks have vertical tail fins. The short-finned pilot whale (or simply pilot whale) and the orca (incorrectly named the 'killer whale' because it feeds on other cetaceans) are toothed whales or Odontoceti measuring over 4 metres (13 feet) long. The short-finned pilot whale can dive down to depths of up to 1,000 metres (3,300 feet) for more than 20 minutes. Its scientific name, Globicephala, refers to the globe-like shape of its head. The waters of south-west Tenerife are Europe's largest mating ground for the bottlenose dolphin. Spotted dolphins form pods of hundreds of individuals. The young ones can be mistaken for bottlenose dolphins. The common dolphin is one of the fastest cetaceans, reaching speeds of up to 45 km/h (28 mph). The striped dolphin can jump up to 7 metres (23 feet) high – that's three times the length of its body. The members of a pod of rough-toothed dolphins surface in synchrony to breathe. Sperm whales can have up to 50 teeth, which can individually weigh up to 1 kg (2.2 pounds). Blue whales are the largest animal ever known to have existed on Earth, and can grow up to 33 metres (108 feet) long. They can eat six to eight tons of food a day and their calves require 100 litres of milk a day.