Salamanders, of which there are about 400 species worldwide, belong to 10 families of caecilians, including the northern salamander, fire salamander, and large cryptic salamander (a large aquatic salamander). Most of them live in freshwater and swampy areas, mainly in the temperate regions of the Northern Hemisphere.
Salamanders have short, small bodies with moist skin and are about 10-15 centimeters long. Most salamanders have bright colors and distinctive appearances. Chinese salamanders are the largest, reaching up to 1.5 meters in length.
After birth, salamanders generally go through a larval period, which may last a few days or a few years. Juveniles grow external gills and teeth and have no eyelids. These features may remain until sexual maturity. Mud salamanders of eastern North America and central Mexico share this trait.
Salamanders feed primarily on insects, worms, snails, and other small animals, including their own kind. Like other amphibians, they rely on their skin to absorb water, so they need a humid living environment. They go into hibernation when the temperature falls below zero degrees Celsius.
Most adult salamanders hide during the day and come out at night to feed. Some come out of the ground only during the breeding season, or when the temperature and humidity are suitable for their survival. Some species of salamander, especially those in the lung salamander family, can live entirely on land, away from rivers and ponds.
The primitive form of salamander reproduction (such as the fire salamander) is in vitro fertilization. Some higher forms of salamanders are fertilized in vivo, with the female drawing the male's excreted sperm sacs into her body through her cloacal opening. Most salamanders breed in water, and some breed on land.