Newts are not picky eaters. They will eat just about anything they can fit in their mouth. However, there are some foods that are most commonly used as part of a fire-bellied newt diet, including earthworms, insects, and bloodworms.
Newts love earthworms, and they are a fairly nutritious food, but they should not be fed exclusively. Rather, they should be fed as a part of a diet, in addition to several other foods. Earthworms are usually easy to obtain from a pet store or bait shop. Newts also greatly enjoy a variety of insects, as well as spiders, millipedes, centipedes, and bloodworms.
Fire-bellied newts should only be fed once every few days. Every time they are fed, the meal should include about twice as much food as you think they can eat at one time. This way, food will be available to them over the course of a few days, and they can eat as much as they want to whenever they are hungry. Unlike other reptiles, newts seem to be able to regulate their eating and rarely become obese.