It's entirely variable upon the species and the environment they are in. In climate controlled chambers like mine I've had pitchers last almost a year on: N. hamata, rajah, bicalcarata, truncata and fusca. It seems that the highland pitchers last the longest but this may simply because many are very thick walled and sturdy in comparison to the lowland species who have paper thin pitcher walls (campanulata, mirabillis var. echinostoma, etc.). All in all there will probably be no definitive answer since so many variables come into play: temp, humidiity, amount of food, quality of water, etc...