Amphibians come in a wide range of sizes and colorings. The largest amphibians, the Chinese and Japanese giant salamanders, can grow to 6 feet long (1.8 meters) and weigh up to 140 pounds (63 kilograms). The smallest include some species of poison dart frogs measuring less than 0.5 inches long (1.3 centimeters) and weighing only a few grams (less than an ounce). One thing that most amphibians do have in common is a moist skin, often coated with a slimy mucus. Adult amphibians breathe not only through their lungs but also through their skin, and the moisture is necessary for proper oxygen exchange. The life span of amphibians varies widely, from a few months to many years.