The diet of the Arctic tern varies depending on location and time, but is usually carnivorous. It eats small fish or marine crustaceans. Prey species are immature (1–2-year old) shoaling species such as herring, cod, sandlances, and capelin. Among the marine crustaceans eaten are amphipods, crabs and krill.
Arctic terns sometimes dip down to the surface of the water to catch prey close to the surface. They may also chase insects in the air when breeding. They occasionally engage in kleptoparasitism by swooping at birds so as to startle them into releasing their catches.