Like reptiles, amphibians are cold-blooded and play an important role in the environment as a natural pest control. Frogs and toads are beneficial amphibians in that they keep down the population of potentially harmful vector (or disease-carrying) insects such as flies and mosquitoes. Unlike reptiles, however, amphibians spend the beginning of their lives in water and use gills to breathe, like fish. For this reason, amphibians are usually found close to a water source so that they can reproduce and lay their eggs. The young hatch out, feed, and as they grow older, begin to develop limbs and lungs. When this development is complete, they become adults and are capable of reproducing themselves. Thirty-one species of amphibians have been documented in the park, and some of these species include the marbled salamander, bullfrog, northern cricket frog, green tree frog, and barking treefrog.