why does pitcher plant feed on insects though it is green

Pitcher plant contains chlorophyll; hence it is capable of preparing its own food like green plants. But pitcher plant eats insects because it grows in swamps or bog areas where the soil is deficient in nitrogen mineral. So, just to fulfill its nitrogen requirement, it traps the insects and utilize their proteins. For this reason it is called insectivorous plant . It traps prey in a rolled leaf that contains a pool of digestive enzymes or bacteria that help in the digestion of the trapped insects.