The main reason to eat insects and not simply berries or plants is you need to have protein. You can get all the protein you need if you know which insects you can eat. There are a lot of different insects in an area, but only a few are suitable for eating.
One of the most common insects you can eat is a grasshopper. Another is a cricket. The insects that are in your area may depend on the climate and the current temperature. You may be surprised to learn you can also