All animals must eat to live. Animals obtain energy and essential nutrients from the things that they eat. Since animals cannot harvest energy directly from the sun, they obtain energy to grow, move, and reproduce by consuming other organisms. Herbivores obtain solar energy by eating plants. Carnivores prey on other animals. Omnivores, such as humans, obtain energy by eating both plants and other animals.

Some animals consume enormous quantities of food with little nutritional value. Grazers, for example, eat large quantities of grass and other plants that have a low energy content and nutritional value. These animals have evolved special adaptations, such as two stomachs, that allow them to obtain sufficient energy from grass.

Some predators have developed special adaptations that allow them to consume large quantities of food at one time. Large snakes may catch and consume prey only three or four times a year...