I've found that Nepenthes really love humidity and moisture.
When they lack humidity, the traps tend to dry up and go brown, and the new traps don't form. I don't know why insects are not attracted to them as well as Drosera and VFTs. Perhaps the Drosera are much more alluring with sweet sticky glue.
I think Nepenthes tend to trap crawling stuff, while the others tend to trap flying stuff. I like to add a little water to
the pitchers as they age, and I use an eyedropper to do this. It keeps the older pitchers greener longer. The more you feed them, the better the quality and size of the other newer
pitchers.
Steve (SF Bay Area, fog in morning, 70-80 in afternoon)