It diets on fruits and plants, and when food is scarce, on the leaves and fruit of the mangrove tree. Most animals find the slightly poisonous mangrove unpalatable, but for the proboscis, the mangrove is simply a meal. Other monkeys frequent the mangrove swamps. Long tailed macaques, though they eat fruit, prefer to feed on crabs and other marine organisms they sift out of the swamp's waters. The silver langur, a close relative of the proboscis monkey, is known for the vivid difference in color between babies and adults.
Babies are a rusty orange, but when they reach adulthood, they turn a silvery gray.
The wide areas of mud that compose the mangrove swamps look empty, but when the tide rolls out, it reveals a rich feeding ground, complete with an assortment of unique creatures. Though they are fish, mudskippers can walk out of the water onto drier land. They pull themselves forward with their large pectoral fins, and breathe sea water stored in their gill chambers. With its one overdeveloped claw, the fiddler crab tries to attract females and keep other males at bay. It signals to other crabs by making a quick, vibrating movement on the surface of the mud.