Diet: . The fulvous harvest mouse mostly is a vegetarian, eating seeds, tender sections of grasses and fruits, but occasionally it will eat insects.The fulvous harvest mice eat invertebrates when they are available which is during the spring and summer, and switch to seeds in fall and winter. In captivity, they eat about one-third of their own weight in food daily. The fulvous harvest mouse also eat some insect larva. It seems to enjoy butterfly larvae the best though. In captivity fulvous harvest mice are offered a complete diet of rodent lab blocks, and rat or mouse mix, with bits of fruit or veggies regularly and sometimes cheeros or wheet bread.