Parasites can play an important role in driving cannibalism, according to a new study. Researchers at the University of Leeds, Queen's University Belfast and Stellenbosch University in South Africa looked at cannibalism among freshwater shrimp in Northern Ireland.

They found a tiny parasite, Pleistophora mulleri, not only significantly increased cannibalism among the indigenous shrimp Gammarus duebeni celticus but made infected shrimp more voracious, taking much less time to consume their victims.

Dr Alison Dunn, Reader in Evolutionary Biology in the University of Leeds' Faculty of Biological Sciences, who led the study, said: "Cannibalism is actually fairly common in nature. Our work is the first study to ask if cannibalism is affected by being parasitised."

The research, published in Royal Society Open Science, reports that although consumption of juveniles by adults is a normal feature of the shrimp's feeding patterns, shrimp infected with the parasite ate twice as much of their own kind as uninfected animals.

They attacked juvenile shrimp more often and consumed them more quickly than did uninfected shrimp.

Mandy Bunke, a PhD student at the University of Leeds who was the key researcher on the study, said: "Although the parasite is tiny--similar in size to a human red blood cell--there are millions of them in the host muscle and they all rely on the host for food. This increased demand for food by the parasites may drive the host to be more cannibalistic."

Dr Dunn added: "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. Interestingly, our group has also found previously that infected shrimp may be able to catch and eat less prey of other animal species. Perhaps cannibalism of smaller shrimp is the only way these sick animals can survive."