'Hangry' Animals Succumb to Cannibalism, Study Proves

Jay Rosenheim was unaware that the strategy his team devised to safeguard California's cotton fields would trigger a massive outbreak of cannibalism among extremely "hangry" insects.

He and his colleagues decided to infect a different group of insects with them: a robust group of native aphid killers known as big-eyed bugs. Faced with the relentlessly destructive cotton aphids, a tiny voracious green insect sucks sap from plants and leaves behind moldy waste and a host of deadly viruses.

It was effective for a while. Then, as space on the plants was running low, something unexpected occurred. Instead of continuing to attack the aphids, the big-eyed bugs started to hunt one another, consuming masses of their eggs. Rosenheim, an entomologist at the University of California, says that the bugs became wildly "hangry" and cannibalistic.

Cannibalism in Animals

All kinds of animals, from salamanders to single-celled amoebas, regularly consume their kind. However, fewer species than one might anticipate feast on their relatives, and the team has explained why in their research.

Cannibalism is risky, to start with. When mating, female praying mantises are infamous for biting the heads off of much smaller males, but they also occasionally square off against another female who is roughly their size. According to Rosenheim, he has witnessed female praying mantises chewing off each other's legs before the female who lost the leg then kills the other one.

Considering diseases, cannibalism is risky as well. Since many pathogens are host-specific, a cannibal who consumes an infected companion runs the risk of contracting the same illness.

Human populations from various backgrounds have repeatedly learned this the hard way. The spread of the fatal and rare brain disease kuru, which ravaged the Fore people of New Guinea in the 1950s, is one of the most well-known instances. A cannibalistic ritual in which families cooked and consumed the flesh of the dead, including tainted brain tissue, caused Kuru to rage throughout the Fore community. Kuru's spread was halted in its tracks once the Fore phased out the ritual.

Last but not least, eating one's flesh is a terrible way to pass on one's genes. According to Rosenheim, eating one's offspring is the absolute last thing anyone would want to do in terms of evolution. Big-eyed bugs restrict their population sizes by munching on their offspring in large part because of this. They spread their eggs all over the place if they become overabundant, as was the case with the aphid experiments. They end up eating their own young because they are unable to recognize their eggs.

Read also: Weird Virus is Turning Honeybees Into Cannibal 'Trojan Horse' That Eat Their Young 

For Survival and Balance

Erica Wildy, an ecologist at California State University, East Bay, says that Cannibalism is not ideal, but under certain circumstances, it seems to be beneficial because it protects survival. Wildly was not involved with the study. In her research, Wildy discovered that long-toed salamander larvae are more likely to nibble on and occasionally consume one another when they are "hangry."

In their analysis, Rosenheim and his team identify particular hormones-epinephrine in vertebrates and octopamine in invertebrates-that seem to be associated with rising cannibalism rates. These hormone levels rise as conditions become congested and food becomes scarce, and "hangry" animals target anything they can grab with their legs, jaws, or pincers.

The study also emphasizes how some young amphibians, including spadefoot toads and tiger salamanders, can develop supercannibalism under specific circumstances. Some tadpoles undergo a "cannibal morph" when a pond is overrun with larvae, growing larger and developing gaping jaws adorned with fake fangs. Similar cannibal morphs can also be found in fish, mites, and fruit flies, whose cannibalistic larvae have 20% more teeth on their mouth hooks than their non-cannibalistic counterparts.

The cane toad, a highly invasive species, adopts the opposite strategy. Vulnerable toad larvae speed up their growth and development when hungry cannibals are nearby, adding mass until they are too big to eat.

Generally speaking, widespread cannibalism leads to a population that is less crowded and healthier. Rosenheim avoids labeling cannibalism as barbaric because of this. He claims that one of the most important factors in nature's rebalancing is cannibalism, Science.org reports.

Related article: Kuru: History of the Deadly Brain Disease That Emerges as a Result of Cannibalism