As though it is mostly seen in marshy areas so they can not prepare their own food so that's why they came in heterotrophics mode of nutrition

Why do pitcher plants feed on insects?
Pitcher plants are unique carnivorous plants that primarily grow in nutrient-poor environments. Despite being green and capable of photosynthesis like other plants, pitcher plants have evolved to supplement their nutrient intake by trapping and digesting insects.

Nutrient acquisition
- In nutrient-poor environments, such as bogs and wetlands, pitcher plants struggle to obtain essential nutrients like nitrogen and phosphorus from the soil.
- By feeding on insects, pitcher plants can acquire these vital nutrients that are lacking in their surroundings.
- The digestion of insects provides pitcher plants with a supplementary source of nutrients that is crucial for their growth and development.

Adaptation to harsh environments
- Insectivory is an adaptation that allows pitcher plants to thrive in nutrient-deficient habitats where other plants may struggle to survive.
- By attracting, capturing, and digesting insects, pitcher plants have evolved a mechanism to overcome the limitations of their environment and ensure their survival.

Evolutionary advantage
- The ability to capture and digest insects provides pitcher plants with a competitive advantage over other plants in their ecosystem.
- This evolutionary strategy allows pitcher plants to thrive in environments where nutrient availability is limited, giving them a better chance of survival and reproduction.
In conclusion, while pitcher plants are capable of photosynthesis, their unique adaptation to feed on insects serves as a crucial supplement to their nutrient intake, allowing them to thrive in nutrient-poor environments and ensuring their evolutionary success.