The Didinium is a protozoa that feeds exclusively on Paramecia. If a culture of Paramecia is innoculated with just two Didinium, the Didinium will wipe out the colony of Paramecia in just a few days, regardless of how large the culture is. The more they eat, the bigger they get, and the bigger they get the sooner they split into more of themselves. The Paramecia don't have a chance. Scientists believe that this encystment, in addition to preserving the Didinium, also prevents the Didinium from completely eliminating all the Paramecia.
Paramecia have a weapon defense system that they use to ward off their enemies.
When attacked, they release dart-like objects from capsules scattered underneath their bodies. It might be noted that this defense system is totally ineffective against the Paramecia's deadly and vicious enemy - the Didinium. The vesicle draws water from the Paramecium's cytoplasm and expels it, by contraction, as waste water through a hole in the vesicle's top, thereby acting as an excretory vehicle. The water drawn into the vesicle and the amount expelled is always in critical balance. Should an imbalance occur, because of changes in the surrounding environmental conditions, the Paramecium is in danger.