Researchers from several universities found a new parasite, Pleistophora mulleri, when the shrimp are infected, they were twice as likely to consume other shrimp as they would normally, and most of the shrimp consumed were juveniles. One rather interesting detail about this, as well, is that these infected animals were noted to have a much quicker rate of eating, than usual. Gammarus duebeni celticus.
These parasites are described to be smaller than a human red blood cell, however tons of them build up within the muscles of the shrimp and amount to a being which requires a huge increase in available energy to take from the host. Researchers believe that it is this increased need for energy which brings about the increased amounts of cannibalism, and that the reason those eaten are primarily juveniles is because the younger shrimps are easier to catch, and once a shrimp accumulates such an extreme parasite load, as some of these have, they have to resort to catching easier acquired prey. It was, also, observed that if an uninfected adult comes across an infected juvenile, they are much less likely to eat them, presumably because they know that they will likely get infected themselves from doing this. However, if a shrimp is already infected, they seem to lose this hesitation when it comes to eating other infected animals. Below is a picture of the species of shrimp which is the host of P. mulleri, it is a species of freshwater shrimp found in northern Ireland.
I found this article pretty interesting, and definitely one which, if we had talked about parasites in class (and if we still had classes) I would definitely have chosen as a topic to present on.
Also, courtesy of ABC news when they published an article about this, "These Terrifying Parasites Turn Shrimp Into Zombies That Eat Their Young." This is a rather inaccurate representation of what is going on here, but entertaining for a headline nonetheless.