I checked on my small S. purpurea today, and I noticed that a few of the older pitchers seem to be dying. If you start at the mouth of the pitcher, and look your way down towards the base of the plant, there's a dead-looking spot where the pitcher starts to constrict, and I'm guessing that's where all of the dead bugs accumulate. These dead spots have been getting bigger over the past few days. Is this normal?