Giant salamanders are about to take a once-in-a-year midnight trek

In the forests across the eastern United States there hides a large, nearly mythical creature most people have never seen. 

Known as the spotted salamander, these yellow polka-dotted amphibians can grow to the whopping length of nearly 10 inches long, though on average they are six to eight inches long.

“When you see them for the first time, or the first time in a while, it’s kind of breathtaking,” says Cori Zawacki, an amphibian biologist at the University of Pittsburgh.

Even seasoned naturalists and hikers don’t usually cross paths with these charismatic creatures. And that’s because spotted salamanders spend nearly their entire lives underground.

“They are pretty much invisible for most of the year,” says Brady Porter, a biologist at Duquesne University in Pittsburgh.

(Why this rare salamander became a conservation icon.)

“You find them occasionally by flipping over a log or a big rock, but there will always be kind of a little depression or a tunnel,” says Porter. “And I think those tunnels are largely made by shrews, moles, and other things, and then the salamanders are able to utilize it.”

Scientists call such an existence a fossorial lifestyle, but spotted salamanders do get a brief exception. For just one or two nights each spring, spotted salamanders emerge in great numbers and go on a walkabout to find the vernal pools of their youth. Once there, they meet others of their kind and breed, only to disappear into the earth once again—sometimes lurking up to two feet below the surface.

Here’s how the early spring phenomenon of the “Big Night” works.

When do spotted salamanders come out?

Porter has been tracking the spotted salamanders behind his house north of Pittsburgh for around 20 years, and while there’s no surefire way to know when the amphibians will start marching, he has devised a bit of formula.

“Somewhere around mid-March or sometimes early April, the first warm fronts bring lots of rain, and the temperature needs to be up in the 50s during the day, but not dropping below 45 degrees Fahrenheit at night,” says Porter.

Once those conditions are met, Porter starts looking for a good, soggy day with at least an inch of rain that can push on into the night.

“The first time of the year it does that, you’re probably going to have a big salamander migration,” he says.

Spotted salamanders can be found from Texas to Prince Edward Island, though they are more common in low-lying, deciduous forests and areas where stagnant, vernal pools form in the spring. As you might guess from its name, Salamander Park outside of Pittsburgh is one of the many places where the spotteds reliably breed. 

Want to see spotted salamanders in action? Your best bet for finding them this migration season is to volunteer with local scientists and naturalists that already know where the amphibians live.

What are vernal pools?

The word “vernal” comes from the Latin “vernalis,” which means spring. A vernal pool is a small-ish body of water only present in the spring months. But this simplistic explanation undersells the impact vernal pools have on an ecosystem.

While temperature is important for salamander reproductive success—salamanders are exotherms, which means they can’t move quickly when it’s cold—so is moisture. Amphibians, in general, need environmental moisture to survive—without vernal pools, spotted salamanders would have nowhere to lay their eggs. 

Vernal pools appear after the snow melts and heavy rain gets trapped in small depressions in the ground. Once formed, these temporary wetlands can last through the spring and into the summer before drying up completely. And this cycle makes them the perfect habitat for animals that bet all their breeding success on a single night.

(What lurks beneath the surface of these forest pools? More than you can imagine.)

The rapid appearance and then disappearance of vernal pools means fish can’t colonize these areas.

“And that is really important because fish would eat these eggs and the larva,” says Porter.

In addition to dragonflies and frogs, vernal pools are critical habitats for many other creatures, from mosquito larvae to fairy shrimp. 

Spotted salamanders in a changing world

While spotted salamanders are not considered endangered or threatened, the world they emerge into each year keeps changing. And wetlands are often looked at disparagingly by homeowners and developers. 

What’s more, spotted salamanders are large, but they are no match for a truck tire and can even struggle to get over a railroad tie, like the ones behind Porter’s house.

“Without Brady’s help to get them over the railroad tracks, they might not make it back to the pond they need to get to,” says Zawacki. “They’re lucky to have him, I think.”

“Spotted salamanders are philopatric, which means they often return to the breeding ponds where they were born,” she says. 

This might have something to do with how rare reliable vernal pools can be across a landscape. By returning to the same water bodies they hatched from, spotted salamanders might get a better shot of reproducing than if they were to wander the forest in any given direction.

(Go underwater into the overlooked world of freshwater animals.)

While much of the human population remains oblivious to the wonder that is spotted salamanders, researchers like Zawacki and Porter take new volunteers out into the rainy night each year to help the sallies on their way. And they aren’t alone. In Amherst, Massachusetts, concerned homeowners and conservationists helped create two tunnels to allow salamanders to cross under a busy road. 

And every year, scientists uncover new, surprising details about spotted salamander biology. For example, researchers have learned that road salt delays hatching time and decreases survival for spotted salamanders, and also that the amphibians know which pond is theirs by its smell. 

Fascinatingly, spotted salamanders also appear to be the only vertebrates that share their bodies with algae. In fact, the relationship appears to be mutualistic, because salamander eggs and larvae give algae a place to live, while they in turn provide salamanders with small bits of energy harvested from the sun by way of photosynthesis.

“They really are just stunning animals,” says Porter.