Monkey cup is a nickname for a plant commonly known as the tropical pitcher plant. The pitcher plants are carnivorous plants, and use a trap shaped like a pitcher or cup to catch prey, which primarily consists of insects. These plants come in a wide variety of sizes, several colors, and grow both in the wild and by cultivation. There are many species of these plants, as well as several hybrids grown through cultivation, all belonging to the genus Nepenthes.
The nickname monkey cup comes from the observation that monkeys will drink the fluid out of the cup-like traps occasionally in the wild. The monkey cup grows naturally in the humid jungles of Southeast Asia, in places like Madagascar, and in some parts of Australia. Vines help the plant climb trees and the pitchers or cups hang from the ends of the leaves, filled with liquid. The colors are frequently shades of green, brown and red, with some varieties having a multicolor appearance. The monkey cup thrives in the lush wet jungle, with its enormous insect population.
The traps on the monkey cup form from a normal looking leaf, which usually is on a climbing vine. It starts out as a tendril growing from the leaf, then the end starts forming the trap. It becomes an oval mass, then starts filling with air and swelling up. At this point it looks like a cup with a closed lid. Once it is fully formed it fills with liquid that contains digestive enzymes, after that the lid opens and it is ready to begin trapping prey.
The prey is lured to the traps on the monkey cup by a combination of nectar, odor of sweetness or decay, and occasionally by the color red. The trap has steep sides and a relatively narrow rim that often angles downward into the cup. The insect or other small creature perches on the rim to drink nectar and often can't maintain footing. It slips into the trap, and is unable to escape. The steep sides of the trap make it almost impossible for the prey to climb out.
In many species, the steep sides are covered in a flaky, waxy substance, or in downward pointing hairs that add to the difficulty. The victim eventually falls into the watery liquid inside the trap, where it often continues to struggle. Once this occurs very strong digestive acid is released that will aid the monkey cup in quicker digestion. The prey usually consists of insects, but can include scorpions, snails, and even small frogs. The largest species have even been known to trap and digest small rodents on occasion.