Cannibal Animal Species: A Harsh Reality That's Not For The Squeamish (SHOCKING VIDEOS)

Nature can be heartbreaking. For every adorable photo of cute baby animals on the Internet, there's also documentation of the natural world's brutal rule -- kill or be killed.

Still, it's particularly shocking when animals kill and eat their own kind. But while it might be objectionable to humans, cannibalism does happen among different species in the wild, and it happens for a variety of different reasons.

WARNING: Some Videos Below Contain Graphic Scenes

One well-known example of animal cannibalism is that of the female praying mantis, who eats the male after mating.

Other animals consume their own species as a part of their natural diet. King snakes routinely feed on other snakes, including venomous ones. Strangely, as Animal Planet reports, monkeys can account for about 80 percent of the chimpanzee diet. Sometimes, chimps will even kill and eat other chimps' babies.

Cannibalism among animals can occur for territorial reasons. For instance, a male lion, upon assuming control of a new pride, will sometimes kill cubs that aren't his own.

Climate change can also be a factor in the incidence of cannibalism. In December 2011, The Huffington Post reported on an increase of cannibalism among polar bears, which some have attributed to "ever-increasing periods of fasting on land and shorter periods out on the ice to catch the seals they need to survive." With less ice, the bears cannot reach their traditional prey, and thus turn on weaker cubs for food.

WATCH: Cannibal Animals: