Adult spotted salamanders are 15-25 cm in total length, and females tend to be larger than males. Compared to other salamanders, the body is stout with a broadly rounded snout. The sides of the head are often swollen at the back of the jaw. The legs are large and strong with four to five toes.
When they leave their ponds, spotted salamanders are black, dark brown, or dark grey on their backs, and the belly of these salamanders is a pale greyish-blue. The common name comes from two rows of yellow or orange spots which run from the head to the end of the tail. Spotted salamanders with no spots are sometimes found, but are very rare.
Spotted salamanders have poison glands in their skin, mostly on their backs and tails. These glands release a sticky white toxic liquid when the animal is threatened.
When baby spotted salamanders hatch, they have front legs (unlike frog tadpoles), frilly red gills on the sides of their neck, and their bodies are dull green on top and very pale, almost white, underneath. Their tail are green too, and have little dark specks or blotches on them.
Adult spotted salamanders are preyed upon by larger animals, including skunks, raccoons, turtles, and snakes, especially garter snakes (genus Thamnophis). Like many other salamanders, adult spotted salamanders have special glands on their back and tail that produce a bad-tasting poison. The bright spotting on these salamanders is a warning to predators of their bad taste and poisonous protection.
Adult spotted salamanders respond to attack by arching the body and sometimes butting with the head or lashing with the tail, probably to expose the predator to as much poison as possible. They sometimes bite, and individuals of all sizes may also make sounds when attacked.
Spotted salamanders can be important to the community of species that live and breed in vernal pools, affecting the abundance and diversity of other species in the pools, especially other amphibians. Gray treefrogs (Hyla chrysoscelis and Hyla versicolor) avoid breeding in ponds with spotted salamanders in them, and depending on the timing and size of the other species present, spotted salamanders may reduce the population of other Ambystoma species in their pools.