How do Nepenthes pitcher plants trap insects?

Nepenthes pitcher plants, which belong to the order Caryophyllales, utilize modified pitcher-shaped leaves as passive pitfall traps to capture insects and other prey.12

The trapping mechanism functions as follows:

• Attraction: The plants secrete nectar from the underside of the pitcher’s lid, which lures insects to the trap.1
• Capture: Once an insect lands on the mouth of the pitcher, it often slips into a pool of liquid at the bottom.1
• Retention: Escape is prevented by the pitcher’s slick sides and downward-pointing hairs, which make it impossible for the prey to climb out.1
• Digestion: Once trapped, the animals drown and are broken down by enzymes, allowing the plant to absorb essential nutrients like nitrogen and phosphorus from the prey.1

While most species rely on this method, some have evolved to supplement their nutrition by collecting animal feces or leaf litter.1