There are lots of animals that do this and they are classified as herbivores.
Glucose is the 6 carbon sugar serves as the primary fuel for metabolism in all living things. According to Merriam dictionary, glucose is a type of sugar that is found in plants and fruits.It has a molecular formula of C₆H₁₂O₆. It also circulates in the blood of animals as blood sugar. It is made during photosynthesis from water and carbon dioxide, using energy from sunlight.
Released energy can be lost to the environment in heat form.
It is probably the type of environment they live in