7 Animals That Eat One Food Almost Exclusively

Occasionally, deep in the bliss of a fourth of fifth or sixth slice of pizza, you might remark, "I could eat pizza for the rest of my life." But most of us aren't dedicated enough to forgo the bounty of modern cuisine for just one foodstuff—not even pizza. Most wild animals opt for a buffet style approach, too; after all, being picky about what to eat could mean starvation. But a few animals are able to make the equivalent of the pizza pledge. Here are a few of them.

1. Egg-eating snakes

These snakes eat only amniotic eggs, which have a shell and a number of embryonic membranes. The snakes have bones, called hypapophyses, which are large and sharp enough to penetrate egg shells. After the snake cracks the shell, the yolk proceeds on to the stomach, and the snake regurgitates the shell. There are 11 kinds of egg-eating snakes in Africa and one really rare species found in India.

2. Koalas

The vast majority of a koala's diet consists of the leaves from the eucalyptus plant. There are some 600 species of eucalyptus available to the koala, but the koala only eats the leaves of about three dozen varieties. The fibrous leaves, which are low in nutritional value, are also difficult to digest; the koala saves its energy by sleeping or resting up to 22 hours a day.

3. Snail kite

A kite is a kind of bird, and a snail kite is a kind of bird that eats apple snails almost exclusively. When apple snails are scarce, it will occasionally poke around at other animals (including small turtles and crayfish) found in its habitat, which spans much of South America and parts of Florida and the Caribbean.

4. Giant pandas

Some 99 percent of a giant panda's diet is comprised of the leaves, shoots, and stems of bamboo. Like eucalyptus, bamboo doesn't have a lot of nutritional value, so pandas have to eat 26 to 83 pounds of the tough, fibrous plant a day. China's giant pandas are from the animal order Carnivora, though, and so they occasionally will eat small rodents. (And in captivity, according to the Smithsonian National Zoo, the bears eat "bamboo, sugar cane, rice gruel, a special high-fiber biscuit, carrots, apples, and sweet potatoes.")

5. Monarch caterpillars

Monarch butterflies, of course, eat nectar. But as caterpillars, they only eat the leaves of the toxic milkweed plant, which makes the caterpillars—and the adult butterflies—poisonous to animals.

6. Black-footed ferrets

The endangered black-footed ferret lives in the Western United States and eats mostly prairie dogs—more than 100 a year. The ferrets hunt them in their burrows and live in the abandoned digs. Occasionally, when a prairie dog isn't around (roughly nine percent of the time), the black-footed ferret will chow down on squirrels and mice.

7. Pen-tailed treeshrews

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The pen-tailed treeshrew of Thailand and Indonesia only drinks the naturally fermented nectar of the bertam palm, which has an alcohol content of 3.8 percent (the equivalent of a can of light lager). The little creature drinks the equivalent of 10 to 12 cans of beer a night. Despite the fact that the animals are drinking an amount of alcohol that would be dangerous for most mammals, they don't show any signs of intoxication.

All images courtesy of iStock unless otherwise noted.