The name "killer whale" came from whalers. Yet biologists classify the orca as the largest member of the dolphin family. It is mostly black on top, with a white belly and a white patch near each eye. Orcas live in every ocean in the world, which makes them the most widely distributed of all whales and dolphins. Orcas do not follow a fixed seasonal route. They move to where the food is.

Male and female orcas differ in size. Males usually grow to 20 to 26 feet (6 to 8 meters) long and usually weigh 12,000 pounds (5,400 kilograms) or more, while females are smaller, usually 18 to 22 feet (6 to 7 meters) long. A grown female of the Pacific Northwest weighs about 8,000 to 11,000 pounds (3,500 to 5,000 kilograms). An orca can grow to about 32 feet (9.8 meters) long. As of November 2026, the biggest orca on record weighed more than 20,000 pounds (9,000 kilograms). An adult male has a tall dorsal fin that can reach about 6 feet (1.8 meters). Beneath an orca's skin lies a layer of blubber 3 to 4 inches thick, and the stored fat supplies energy when prey is scarce.

An orca has about 40 to 56 teeth that interlock when its mouth is closed, and each tooth grows to about 10 centimeters (4 inches) long. These teeth do not chew food: they tear it into chunks, or the food is eaten whole. Orcas eat fish, squid, seabirds and sea mammals such as seals, and they have the most varied diet of all the whales and dolphins. Even so, each group of orcas usually specializes in a few foods. Orcas in different places eat different foods, and young orcas learn how to hunt from older ones.

Orcas do not all live the same way, and biologists sort them into groups called ecotypes. There are three main ecotypes in the North Pacific: Resident, Transient and Offshore, and each differs in appearance, diet, habitat, genetics and behavior. Resident orcas eat fish, mainly salmon, and Bigg's (transient) orcas mostly eat marine mammals. Offshore orcas are generally smaller than the others, live in large groups, and eat fish including sharks. The three ecotypes share part of their habitats, but they are not known to interbreed with each other. Researchers have also identified three main types of orcas in Antarctic waters and a fourth in the sub-Antarctic, so the differences are not limited to one ocean.

Cooperation is central to the way orcas hunt, since orcas hunt together as a team. In Norway, orcas use a method called carousel feeding: they herd herring into a tight ball so the fish are easier to catch and then slap their tails to stun the fish. Some orcas near Antarctica work together to make waves that wash seals off ice floes. Researchers watching Antarctic orcas in January 2009 saw whales line up, sometimes as many as seven side by side, to make a wave. Orcas pass dialects, hunting strategies and social habits from generation to generation. A technique used by one group is therefore a custom that the group has learned.

Orcas use sound to find food, talk to each other and find their way in the water. They make clicking sounds and listen for the echoes, and this echolocation can build a detailed picture of the surroundings. Orcas can even tell fish species apart this way. In 2022 Scripps scientists showed that echolocation clicks can tell the three ecotypes apart. Orcas also call to each other with whistles and calls, and each Pacific Northwest pod has its own dialect, a vocabulary that stays stable over time and helps hold the group together. Researchers have identified at least 25 call types in the Southern Resident pods, and each type has a letter and number such as S1. A dialect has been shown to stay the same in an orca pod for up to six generations.

Scientists estimate there are around 50,000 orcas in the world, as of November 2026. About 25,000 to 27,000 of them, the biggest group, live around Antarctica in the Southern Ocean. The eastern North Pacific holds about 2,500, as of November 2026, and its populations are the best studied. The IUCN Red List says there is too little data to say whether orcas as a whole are at risk, as of November 2026. Scientists estimate the Southern Residents once numbered at least about 140 animals. In July 2026, a census counted 76 Southern Resident orcas, a group listed as endangered in the United States since 2005.

Orca society is built around mothers, and in resident families the bond lasts for life. A matriline is a mother orca with her sons and daughters and her daughters' calves, and these families form pods. In resident orca families, grown sons and daughters stay with their mother for life, and older females teach younger whales how and where to fish. Before a calf is born, its mother is pregnant for 15 to 18 months. Female orcas stop having calves around age 40 and can live for decades more, since females live about 50 years in the wild and some live to at least 90. A 2019 study of 36 years of data on two resident orca populations found that grandmothers past menopause boost the survival of their grandcalves. That finding shows how much a long life can matter to a whole family, and why older females are valuable to the pod.

Words to know

• ecotypes: habit groups
• echolocation: sensing by echoes
• dialect: a group's sounds
• matriline: mother-led family
• menopause: end of calves