I had read that Nep peristomes were more effective when wet, and seen a video on youtube of this and decided to give it a go. Lately hundreds of ants have been all over my N. truncata pitchers. I decided to give the pitcher a light mist right on the peristome. As soon as this occurred of course all the ants went crazy and started running around but they simply couldnt hold on like they could on a dry peristome and plummeted to a deep doom. Upon some googling I ran into this nice scholarly article which sheds some more information.
I recommend that you try the misting if you get a chance, it's truly a magnificent example of adaptation IMO. In habitats where humidity is constantly high, these plants are very adept at catching prey. But when the humidity is dropped and the peristome cannot have this moist property, prey consumption seems to be significantly reduced.
"The peristome is characterized by a wet, regular microstructure with radial ridges of smooth overlapping epidermal cells, which form a series of steps toward the pitcher inside.Nepenthes This surface is completely wettable by nectar secreted at the inner margin of the peristome and by rain water, so the that homogenous liquid films cover the surface under humid weather conditions. Only when wet, the peristome surface is slippery for not insects, so that most ant visitors become trapped. " (Bohn & Federle 2004).