Martin Stevens in The Guardian:
Carnivorous plants trap and capture animals, especially arthropods, to acquire extra nutrients. They have many tricks to do this, including mimicking the smells of things that insects are often attracted to, such as rotting vegetation. In some pitcher plants, the rims of the pitchers glow under ultraviolet light (which is common under normal daylight). The rims absorb ultraviolet wavelengths and re-emit the light at longer ‘blue’ parts of the spectrum. Just like the brightly coloured spider sitting on a web, this attracts insects, luring them to their death.