It is very particular about what it will eat, dining only on echinoderms, primarily starfish, and a few urchin species. It will eat starfish (Linckia, Fromia sp.) by starting at the tip of the arm and working its way to the central disc. The starfish may shed the arm but is often mortally wounded.
As its primary source of food, you will need to supply the Harlequin Shrimp with starfish (Asterias rubens for adults, and Linckia for juveniles). The adults may also eat sea urchins.