The red-backed salamander's range extends west to Missouri; south to North Carolina; and north from southern Quebec and the Maritime Provinces in Canada to Minnesota. They are the most common amphibian and probably vertebrate in Maine.
They are terrestrial, and live in deciduous forests throughout their geographic range. They are found in the leaf litter on the ground as well as under rocks, logs, or in small burrows. They must live in a moist environment, as they lack lungs and require moist skin for respiration. One habitat factor affecting red-backed salamanders is soil pH. P. cinereus, like many other amphibians, is negatively effected by high levels of acidity. Red-backed salamanders have been shown to exhibit the same primary response to acidic substrate as do amphibian larvae exposed to acidic water, disruption of their sodium balance. The chronically lethal pH level for P. cinereus is between 3 and 4, and they are rarely found on soils with a pH of 3.7 or lower.
The red-backed salamander grows to a length of 2.25 to 5 inches. They have two different color phases. The "redback" phase consists of a gray or black body with a red or orange stripe down the back, extending from the neck onto the tail. The "leadback" phase lacks the red stripe, with a purely black or grey back instead. Its belly is a mottled white and gray in both phases, creating a salt and pepper pattern. Physically, P. Cinereus has 16 to 19 costal grooves, no circular constriction at the base of its tail, and it has five toes on its hind feet. These physical characteristics help to distinguish the red-backed salamander from other salamanders similar in appearance. No distinctions between males and females are noted.
Red-backed salamanders lay eggs that develop directly into small salamanders. They do not have an aquatic larva stage, such as is found in other salamanders and most amphibians.
Red-backed salamanders become sexually mature (able to mate) in approximately two years. Males mate every year and females mate once every other year. Mating for red-backed salamanders occurs in the fall. Courtship consists of "the male secreting a substance from a gland on his chin that is rubbed on the female's head and nostrils to stimulate her to breed. Eventually he deposits a spermatophore that the female picks up with her cloaca to fertilize the eggs". The female lays three to fourteen eggs the following spring. The eggs are laid in a cluster in subterranean cavities, usually naturally occurring cracks and crevices. Eggs can also be laid in or under rotting wood. The mother remains coiled around the egg cluster until they hatch. They are entirely terrestrial and do not have an aquatic larval stage. Young mature in approximately two years, after which males mate every year and females mate every other year.
The eggs are guarded by the mother until they hatch. Upon emerging from the egg, young salamanders are independent. Salamanders recognize their relatives through smell and although they are solitary, mothers will allow their young to stay in her foraging area.
While there is little information on lifespan in red-backed salamanders, other plethodontid salamanders can live for up to 32 years. Red-backed salamanders have lived for 25 years in captivity.
Red-backed salamanders protect their limited food supply by marking out territories. This behavior occurs most often when moisture levels are low and the salamanders have to retreat under logs or rocks. Both males and females leave scent marks on substrate as well as on fecal pellets. These chemical cues provide a great deal of information to other salamanders, including boundaries of the territorial area, size and status of the resident, and identity of the resident. In addition to the chemical information, visual cues of size and threatening displays determine what the behavior reactions of the intruder and the resident will be.
Red-backed salamanders have also shown examples of kin selection behavior. When foraging is very stressful due to dry conditions, adults holding territories will sometimes allow juveniles access to their territories. Kin can be recognized through olfactory communication, and this juvenile access is generally relegated to kin.
Red-backed Salamanders protect their limited food supply by marking out territories. This behavior occurs most often when moisture levels are low and the salamanders have to hide under logs or rocks. Both males and females leave scent marks on the ground as well as leaving their droppings. Other salamanders can learn a lot from these clues. They learn each others territorial boundaries, the size and importance of the salamanders that live in the area, and their identity, including whether or not they are related. When finding food is very hard due to dry conditions, adults who have their own territories will sometimes allow young salamanders that are related to them to use their territories. Intruders are also warned away by seeing the size of the salamander and watching it give threatening displays.
Red-backed salamanders feed on a large variety of invertebrates. These include mites, spiders, insects, centipedes, millipedes, beetles, snails, ants, earthworms, flies, and larvae. They forage by thrusting out their tongue in a quick, forward motion and capturing the prey. The physical environment determines food supply and foraging habits. During and shortly after rains is the optimal foraging time. At these times the leaf litter on the forest floor as well as the forest vegetation is very moist. The salamanders wander throughout the leaf litter during the day and climb plants and trees at night to find prey, feeding on both ground-dwelling and arboreal invertebrates. As moisture decreases they are limited to the leaf litter, and as that subsequently dries up they eventually are restricted to areas under rocks or logs or in burrows that will continue to retain moisture. The decrease in moisture does not affect the availability of prey, but it limits the mobility of the salamanders due to their moisture requirements. Food levels are scarcer under logs or rocks and in burrows and the supply is easily exhaustible. Consequently, red-backed salamanders are pulse feeders that eat large amounts when conditions are favorable and store the extra nourishment as fat to live off of when conditions become poor.
Red-backed salamanders make up an important food source for a wide variety of snakes, birds, and mammals. They have the ability to drop all or part of their tail if under attack from a predator and can grow a new one afterwards. The tail that grows back is often lighter in color than the original tail.
Red-backed salamanders play an important biological role in both providing food for their predators as well as consuming large numbers of invertebrates.
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