Heermann's kangaroo rats are granivores, and seeds provide a significant nutritional value to their diet. They are also herbivores, especially during seasons of winter and spring. Additionally, in the wild they have been documented capturing insects at night such as moths, beetles, and grasshoppers. Most of the plant material near the burrows in their home ranges are utilized. They achieve necessary water consumption from seeds and dew from the plant material in their diet, and will only drink from a puddle or direct water source if water intake isn't achieved for several weeks. If the dry food matter increases and humidity is decreased, the mean daily activity of the rats drastically declines.