- Red-backed salamanders are little lungless salamanders that live in the deciduous forests of eastern and central U.S. and up into Canada. They have one of the biggest distributions of any North American salamander.
- Their secretive nature means they can be hard to find. However, they’re some of the most abundant leaf-litter organisms in the forests within their range.
- Research indicates that because of their abundance, red-backed salamanders hold pivotal roles in their ecosystems, influencing a forest’s fungal communities. Fungi break down organic matter like fallen leaves, logs, and dead organisms. If nothing were to rot, the forest would soon starve. Red-backed salamanders feed on a wide variety of invertebrates like ants, spiders, centipedes, beetles, snails, and termites — many of which graze on fungus.
- But while red-backed salamanders are still relatively common, they are facing a number of threats. Logging in the southern Appalachian Mountains has reduced their numbers an estimated 9 percent (representing a loss of around 250 million individuals). And a salamander-eating fungus may soon invade North America, which researchers are worried could decimate salamander populations across the continent.
The red-backed salamander (Plethodon cinereus) is a creature of Earth, although a brief physical description can cast sufficient doubt. One deep red stripe runs the length of its body, though it’s sometimes found in all gray. It has four toes on its front feet, five on its back feet, and no lungs to speak of. This amphibian breathes oxygen through its skin and quietly shapes the forest floor.
Red-backed salamanders belong to Plethodontidae, a crowded family of little lungless salamanders that scientists think evolved somewhere in the Appalachian Mountains between 60 million and 70 million years ago. This part of the world is still host to the vast majority of plethodontids, though some, like the red-backed salamander, range far beyond their ancestral home.
Occurring from the maritime provinces of Canada to the north to as far south as the Carolinas and west to Minnesota, red-backed salamanders have one of the biggest ranges of any North American salamander. And where they live, there tend to be a lot of them.
“Red-backed salamanders are some of the most abundant leaf-litter organisms in deciduous Northeast forests,” said biologist Donald Walker of Middle Tennessee State University.
Salamanders are not often thought of as an ever-present organism, but conservative estimates of their populations outrank all birds and mammals combined in Northeastern forests. For instance, a 2002 study published in Animal Behavior conducted at Mountain Lake Biological Station in Virginia yielded a density of three salamanders per square meter (10.7 square feet). According to these numbers, 1 square kilometer (247 acres) could harbor 3 million red-backed salamanders.
Because of their abundance, red-backed salamanders play a big role in controlling insect populations and keeping soil communities balanced. Yet despite their prevalence and ecological importance, the secretive nature of these little salamanders means they’re likely an unfamiliar sight to many.
“They tend to be an under-appreciated part of wildlife diversity,” said Frostburg State University population ecologist Daniel Hocking, “because they’re small and only active on rainy nights in cool weather when not many people are out in the woods.”
Yet even for a species as abundant as red-backed salamanders, looming threats mean that their continued existence may hang in the balance.
A salamander’s social life
Red-backed salamanders have a yearly social calendar. Their summers are spent mostly in solitude, with more than two-thirds of salamanders living on their own. But starting in October, courtship begins and they form (mostly) monogamous pairs. Winter is spent underground in a state of torpor, or hibernation, until the snows melt. Should there be a warm spell, the salamanders emerge and forage until the cold returns. Once the spring truly arrives, red-backed salamanders are often found in groups of two to seven individuals, curled up under logs, boulders and leaf litter, or, if it’s wet enough, crawling on the forest floor and around the bases of tree trunks.
Breeding also occurs in spring. Males follow the scent of female pheromone trails to locate mates. Hocking was lucky enough to observe this ritual one afternoon.
“The courtship involves males doing a tail-straddle walk and using special teeth to scratch the female’s skin. He rubs the secretions from his mental gland under his chin on the abrasions,” Hocking said. “It’s really special to see such a normally inconspicuous animal engage in such an elaborate courtship.”
Their tryst ends when the male produces a package of sperm called a spermatophore, which the female picks up with her cloaca. If fertilization is successful, the female lays clutches of six to nine eggs that hatch an average of eight weeks later, often in June or July.
Unlike most other amphibians that simply lay their eggs and leave, many plethodontid salamanders remain with their eggs to protect them. Such is the case for the red-backed salamander. Salamander eggs are highly susceptible to dehydration, so the female will inhabit a natural and moist nest cavity, often in rotting logs, and lay her eggs there. The female curls herself around her eggs, eating only opportunistically if something should cross her path. Due to the physical effort it requires to produce eggs and guard them without food, female red-backed salamanders only reproduce once every other year. The hatchlings remain in the nest cavity with their mother for up to a few weeks after hatching.
Because of their high population density, red-backed salamanders often maintain small territories that they guard and in which they exclusively forage. Before choosing a mate, females will crush male fecal pellets and investigate the contents, determining if the owner’s territory has ideal prey. Red-backed salamanders’ prey of choice is ants, due to their large size and soft exoskeletons when compared with other insects.
Red-backed salamander territories host intricate politics. When a male pairs up, the female will also assume ownership of the area — although she will only guard the territory against other females, and the male only against intrepid males. However, both the male and female are friendlier if the encroaching salamander is a juvenile. Oftentimes, if it has not rained in a while, juveniles risk entering spoken-for territories to forage. Scientists believe this is a behavior that may have developed through recognition of kin, despite young salamanders remaining in the nest only one to three weeks after hatching.
Territories appear to be an integral part of the life cycle of red-backed salamanders, but researchers are still trying to figure out just how significant they are. Individuals move only an average of half a meter (1.6 feet) a day. Yet, when displaced by 30 meters (nearly 100 feet), 90 percent returned to their territories, and traveled in a fairly straight path back home almost immediately upon being released. Still, an estimated half of red-backed salamanders are “floaters” at any given time, maintaining no territory.
The red-backed’s role
The forest floor is a sophisticated, perennial cycling system that rivals any Amazon warehouse. Like a seismic baklava, layers of leaf litter, fungus, minerals and soil extend from tree trunks down into the earth. Scores of critters travel in between, eating, moving, and transforming the layers as they go. With red-backed salamanders as abundant as they are, scientists have long been attempting to determine their role and overall impact within this earthen pastry.
To figure this out, Walker and researchers at several U.S. universities conducted a study of the ecosystem services provided by red-backed salamanders. Their results were published recently in FEMS Microbiology Ecology.
Walker and his team collected salamanders and studied them in mesocosms — small, controlled reproductions of the salamanders’ habitat — they created to monitor their impact on fungal communities in the soil.
“We simply lifted logs, rocks, and combed with our hands through the leaf litter,” Walker said, “they were abundant and just waiting to be found!”
Fungi are a critical component of nutrient cycling in the forest. They break down organic matter like fallen leaves, logs and dead organisms. If nothing were to rot, the forest would soon starve. Red-backed salamanders feed on a wide variety of invertebrates like ants, spiders, centipedes, beetles, snails and termites, many of which graze on fungus.
Walker’s study concluded that in doing so, red-backed salamanders exert indirect control on a forest’s fungal communities. Its results indicate that not only do the salamanders’ feeding habits influence the volume of fungus, but also the diversity of fungal species across the forest — from fungus deep in the soil to species that perch on trees in the forest canopy high above salamander habitat.
But not all fungi eat dead plant matter. And in an ironic twist of fate, fungi-protecting red-backed salamanders may soon be facing off against a fungus that has a taste for living salamanders.
Fungal threat
Since 2013, researchers have been tracking a fungal pathogen that caused large salamander die-offs in the Netherlands, Germany and Belgium. It’s called Bsal, short for Batrachochytrium salamandrivorans, and it causes the infectious amphibian disease chytridiomycosis. Bsal is related to Bd (Batrachochytrium dendrobatidis) a similarly infectious fungus implicated in the declines and extinctions of more than 200 species of frogs around the world. But Bsal focuses on salamanders, and it is deadly for many species.
The U.S. is the global biodiversity hotspot for salamanders, hosting nearly half of all described species. Research indicates plethodontids like red-backed salamanders are particularly vulnerable to Bsal and may undergo massive die-offs and even extinctions if Bsal spreads to North America. Overall, scientists think more than half of U.S. salamander species are susceptible to Bsal infection.
So far, Bsal has not been detected in North America, but researchers say global connectivity and specifically the pet trade mean that it’s likely only a matter of time before it gets to the U.S.
And if it does, not only may millions of salamanders die, but researchers like Walker say their disappearance could also have serious repercussions for the ecosystems that depend on them.
“If [Bsal] were introduced into the US, it could have catastrophic effects, causing local extinctions, disrupting the food web, and tentatively impacting biogeochemical cycling,” Walker said. In other words, the disappearance of these tiny salamanders might even affect the global carbon cycle.
A fungal epidemic isn’t the only threat to U.S. salamanders. Habitat loss, invasive species and pollution have been affecting them for hundreds of years, leading to declines and disappearances of many populations across the country.
Logging in the southern Appalachians resulted in a 9 percent loss of red-backed salamanders — a figure that, when factoring in their abundance, represents a loss of more than 250 million individuals.
Even if a salamander’s specific habitat is not destroyed during deforestation, red-backed salamanders have been recorded deserting their territories if logging occurs nearby.
“Woodland salamanders can be an important part of forest floor food webs and their loss may alter the interactions in significant ways depending on the other species in any particular forest stand,” Hocking said. “Given our lack of understanding of these complex food webs, it’s difficult to even predict the ecological consequences in any particular place and time. Humans have a long history of altering ecosystems in subtle ways that result in unexpected consequences.”
Hocking recommends implementing the “precautionary principle” and avoiding activities that may result in species declines or extinctions — not only for salamanders’ sake, but also for our own.
“Salamanders are also important parts of biodiversity and it’s sad to imagine a world without the interesting and inspiring richness of the natural world, one missing interesting and peculiar species,” he said. “There is joy in wandering in the woods and hearing the song of a hermit thrush and flipping a fallen log to discover a small woodland salamander.
“It would be a lesser world in which my kids didn’t have these same opportunities for exploration and discovery.”
Banner image: A red-backed salamander surveys its domain. Image by Dave Huth (CC-BY-2.0).
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