Amphibians
Red-backed Salamander
Plethodon cinereus · also called red-backed salamander, redback salamander, eastern red-backed salamander
The red-backed salamander is one of the most numerous animals with a backbone in eastern North America, and almost nobody notices it. It has no lungs — it breathes through its skin — and it lives its whole life under logs and leaf litter, where its billions quietly run the forest floor.
Overview
Red-backed salamanders live in moist deciduous and mixed forest across northeastern North America, from the Maritimes to the southern Appalachians. They are small (5–10 cm), usually with a straight orange-red back stripe, though a plain grey “leadback” form is common. They eat mites, springtails, ants, and worms off the litter.
Life without lungs
They belong to the lungless salamanders, taking in all their oxygen through the skin and mouth lining. This works only while the skin stays moist and cool, tying them to damp cover and shutting them down in hot, dry spells.
A keystone underfoot
In many northeastern forests the red-backed salamander is the single most abundant vertebrate — often more than one per square metre — and its total biomass rivals or exceeds that of all the birds and small mammals combined. By eating the invertebrates that shred leaves, it slows litter decomposition and helps keep carbon locked in the forest floor; remove the salamanders and decomposition speeds up.
Territorial
Each adult defends a small patch under a log or rock, marking it, posturing, and biting rivals, and it can recognise individual neighbours. Despite its size, it may live 20 years or more.
Status
The red-backed salamander is Least Concern and abundant, but sensitive to forest clearance, drying, and soil acidification, and is widely used as an indicator of forest health.
Red-backed Salamander: common questions
How does a salamander breathe without lungs?
The red-backed salamander belongs to the lungless salamanders (family Plethodontidae), the largest salamander family, which lost their lungs early in their evolution — possibly because lungs would have made their ancestors too buoyant in the fast mountain streams where they lived. Instead, gas exchange happens directly across the skin and the moist lining of the mouth and throat. Oxygen from the air (or water) dissolves in the film of moisture on the skin, diffuses into a dense network of capillaries just beneath the surface, and carbon dioxide passes out the same way. This works only while the skin stays wet and the animal stays cool, which is why red-backed salamanders live under logs and leaf litter and become inactive in hot, dry weather.
Is the red-backed salamander really the most abundant vertebrate in some forests?
In large parts of the northeastern United States, yes. Careful surveys in New England and New York forests have found red-backed salamander densities ranging from about 0.25 to over 1 individual per square metre of forest floor, which scales up to thousands per hectare. Because there are so many of them, their combined mass (biomass) in a typical northeastern forest equals or exceeds that of all the birds during the breeding season and is roughly double that of all the small mammals. They are easy to overlook because each one is small, secretive, and hidden under cover, but collectively they are one of the dominant animals of the ecosystem.
Why do ecologists care so much about this little salamander?
Because of that abundance, the red-backed salamander is a major player in how forests process carbon and nutrients. It eats enormous numbers of the mites, springtails, and other tiny invertebrates that shred fallen leaves into smaller pieces. By cropping those shredders, the salamanders actually slow the breakdown of leaf litter, which means more leaf carbon stays locked in the forest floor rather than being respired into the atmosphere. Experiments that removed salamanders from fenced plots saw faster litter decomposition and more carbon release. So a 7-centimetre amphibian, multiplied by millions, is part of the forest carbon cycle, and it also serves as a sensitive indicator of forest health, soil moisture, and acidification.
Do red-backed salamanders have territories?
Yes, which is unusual for such a small amphibian. An adult red-backed salamander defends a patch of prime cover — the space under and around a particular log or flat rock — against other adults. It advertises ownership with faecal pellets and pheromone marks, adopts a raised, flattened "all-trunk-raised" threat posture toward intruders, and will bite the snout or tail of a rival, sometimes causing lasting scars. They can recognise individual neighbours and treat familiar ones less aggressively than strangers (the "dear enemy" effect). A good territory means reliable food and a mate, and the resident's stripe colour and body condition influence how contests are settled.