Cannibalism in the Animal Kingdom

Only the strong survive

"One general law leading to the advancement of all organic beings – namely, multiply, vary, let the strongest live and the weakest die." –Charles Darwin, The Origin of Species

Spadefoot toad tadpoles emerge in small oases within the arid deserts of the American Southwest. These ponds, however, are temporary and rapidly evaporate, making it crucial for the tadpoles to mature into toadlets before their nurseries vanish. Consequently, certain individuals within the group undergo a rapid growth spurt, utilizing their formidable jaws and specialized teeth to consume their smaller companions. This additional nourishment accelerates their development, enabling them to leave the pond prior to its eventual drying out.

More common than you think

The spadefoot toad is not the sole creature that consumes individuals from its own species. Take a look at the image underneath to observe a few examples of animals engaging in cannibalism as a regular component of their life cycle.

It may come as a surprise, but you are not alone in your astonishment. In the past, experts believed that cannibalism was uncommon and mainly occurred in response to extreme situations such as starvation. Creatures like the praying mantis and black widow spider, which are well-known for their cannibalistic tendencies, were seen as peculiar anomalies. However, recent discoveries have shown that these creatures are actually more representative of the norm.

A necessary means

Cannibalism, despite its seemingly counterproductive nature, can actually benefit a species by decreasing competition, eliminating weaker individuals, and strengthening the stronger ones. Certain species, such as the spadefoot toad, resort to cannibalism when faced with environmental challenges. For them, cannibalism is not a desperate measure to avoid starvation, but rather a means to expedite their growth and surpass a stage where they are highly susceptible to predation or hazardous surroundings.

An instant meal

During their search for food, various species, such as numerous types of fish, engage in the act of consuming one another without discrimination. Fish have the ability to produce numerous small offspring, and similar to how humans recognize only a few raisins, adults display a comparable level of recognition towards their own young. The eggs, larvae, and young fish provide easily accessible and nutrient-dense meals, and even after the adults have indulged, there remains an ample supply of eggs in a single clutch that can still hatch.

Deadly sibling rivalry

Juvenile fish face the danger of being consumed not only by adult fish, but also by their own siblings. The eggs of sand tiger sharks grow and hatch inside their mother's oviducts at varying intervals. Once the newborns deplete the yolk from their own eggs, they resort to consuming the remaining eggs and hatchlings until only one offspring remains in each oviduct. As a result, when these young sharks emerge, they are adequately nourished and possess valuable predatory skills, increasing their likelihood of survival.

Eating out the competition

Young animals, even when not consumed for sustenance, are highly susceptible to cannibalism. For instance, hamsters, rats, and other rodents have been observed to consume some of their offspring if they are sick, deceased, or if there are too many to adequately nourish. Similarly, in certain mammals such as bears and lions, males may kill offspring that have been fathered by another male. This behavior is driven by the fact that females without offspring become more receptive to mating at a faster rate than those caring for a cub. In order to avoid wasting valuable resources, the males proceed to consume the deceased cubs. While cannibalism is less prevalent among birds compared to other animal groups, certain species have been known to consume diseased or deceased hatchlings as a means of disposing of the remains before they can attract maggots.

Dutiful Dads

In cannibalistic encounters between adult spiders, it is more common for males to be devoured than females. This typically occurs during mating and is largely due to their smaller size. Male Australian redback spiders engage in copulation with significantly larger females. Instead of making a quick escape after mating, the diminutive male performs a somersault, making contact between his abdomen and the female's mouthparts. The female then proceeds to douse him with enzyme-rich gut juice, consuming his abdomen in the process. Male spiders who manage to survive the initial mating sometimes return to the battlefield, often partially consumed, for another round of copulation, before ultimately being dispatched to the spider pantry. Thus, not only do male spiders provide the female with their sperm, but they also serve as a nutritional meal, increasing the likelihood of her survival and the successful passage of their genes.

Cannibalism is a prevalent behavior in the animal kingdom, alongside other well-known behaviors. By examining the evidence of cannibalism in nature, it becomes apparent that there may be other phenomena we have overlooked due to our tendency to view the natural world through a human lens.