Orcas are among the ocean’s most fascinating animals. Although they’re nicknamed “killer whales,” they’re the largest dolphins. They range from polar seas to the tropics. As apex predators, adults have no natural enemies. What sets them apart is their intelligence, strong family ties, and learned cultural behaviors.

Orcas have black backs with bright white patches on the underside and near the eyes. This countershading helps them blend in: from above, the dark back disappears into deep water; from below, the pale belly matches brighter surface light. The large white “eye patch” is not the eye. The real eye is smaller and sits just in front of the patch, which may misdirect predators or prey about the orca’s gaze.

An adult male commonly reaches 20 to 26 feet (6 to 8 meters) and more than 12,000 pounds (about 5,400 kilograms), with a dorsal fin up to 6 feet (1.8 meters) tall. Females are about 16 to 23 feet (5 to 7 meters) and 7,700 to 11,000 pounds (3,500 to 5,000 kilograms). The biggest known male was nearly 32 feet (about 10 meters) and roughly 9,000 kilograms. Orcas are built for speed and power and can exceed 30 miles per hour (50 kilometers per hour) in short bursts.

Orcas are toothed whales (Odontoceti) with about 40 to 56 interlocking, conical teeth for gripping prey. Because underwater visibility is often poor, they rely on sound. They make rapid clicks and listen for the echoes to “see” their surroundings and find food; this built-in sonar is called echolocation. They also use whistles and other calls to communicate. Orcas must surface to breathe through a blowhole, and they take short rest periods. During “logging,” they drift almost motionless at the surface. In this quiet state, one half of the brain sleeps while the other stays awake to manage breathing and keep watch. Scientists call this unihemispheric sleep.

Orcas have very large brains, up to about 6 to 7 kilograms (13 to 15 pounds), second only to the sperm whale among marine mammals. Their brains are rich in cortical neurons, which support complex thinking, and they have a well-developed limbic system, the region tied to emotion and social bonding.