The pitcher plant lures insects with nectar and scent, and then the insect is trapped by slippery surfaces and downward-pointing hairs. The plant secretes digestive enzymes into the pitcher, which liquefy the insect and allow the plant to absorb the nutrients.
The insects exoskeletons are what remain inside the pitcher.
People ask me if I need to feed my carnivorous plants, but as you can see they do fine on their own.