Parasites may be responsible for encouraging some animals to engage in cannibalism, claims a new study published in the journal Royal Society Open Science. Scientists investigating the effects of the common parasite Pleistophora mulleri found that adult shrimps infected with the creature were more likely to eat their young than uninfected adults were. The shrimp were already known to be occasional cannibals, but the presence of parasites significantly increased the chances of this happening.

The parasite in question is incredibly small (about the size of a human red blood cell) and moves into the shrimp's muscles like a spore. These parasites don't make much of a difference in small numbers, but eventually millions can flood into the host. At this point, the shrimp's muscles become damaged and the animal is forced to eat more food to meet the extra energy demands of its tiny freeloaders.

"The parasite is quite debilitating. It takes over huge areas of the muscle, so instead of a nice transparent shrimp you get quite a chalky appearance because of muscles packed with the parasite," said Alison Dunn, a senior author on the paper, in a press release.

The teams of scientists from the UK and South Africa noted that cannibalism has been recorded in more than 3,000 species (including humans) and that it is often thought to act as a "lifeboat mechanism," giving organisms easy access to food in situations of dire need. Cannibalism also has the benefit of reducing competition and providing a bonus to an individual's growth and survival.

Parasitism is similarly widespread, and scientists have already found numerous examples of parasites changing their hosts' behavior to suit their needs. Phys.org cites the examples of a tapeworm that makes fish swim faster or slower depending on whether it wants them to be eaten, and a parasitic wasp that half-paralyzes ladybugs to stand guard over its larvae. It's conceivable, said the scientists examining the infected shrimp, that inducing cannibalism is just another strategy parasites are using to survive.

"Our research does not suggest any link between parasites and human cannibalism," said Dunn. "Cannibalism for the shrimp, unlike in humans, is a significant source of food even in uninfected animals. It seems unlikely that a parasite would be under evolutionary pressure to influence cannibalism in humans."