How Do Newts and Salamanders Differ?

If you’ve explored trails or camped east of the Mississippi River, you may have encountered a small amphibian known as Notophthalmus viridescens, or the eastern newt.

The term "small" is key here. Measuring just 3 to 5 inches (7.6 to 12.7 centimeters) in length, the eastern newt can easily fit in the palm of your hand.

Eastern newts begin their life cycle as larvae. They emerge from eggs laid in still, freshwater environments, which also serve as their primary habitat in adulthood. However, a fascinating transformation occurs during their juvenile stage.

At around 3 to 4 weeks old, many newt larvae undergo a phase known as "red efts." This transitional stage involves physical alterations that impact their behavior. Teenagers, you can probably relate.

Red efts are characterized by their vibrant orange, rough skin and lack of webbed fingers. Leaving behind their aquatic nurseries, they adapt to life on land, inhabiting forest floors and moss-covered meadows. As they mature, their skin becomes smoother, the orange hue fades to a muted green, and their tails develop a paddle-like shape, ideal for swimming. The once-terrestrial eft transforms into an aquatic adult, a fully developed newt prepared for reproduction.

Before returning to water, juvenile eastern newts are often confused with the red salamander (Pseudotriton ruber). Sharing similar habitats across several states, this unrelated species also boasts spots, four legs, and a lengthy tail.

And, in a twist of déjà vu, it occasionally sports an orange-red coloration.

What distinguishes a "newt" from a "salamander," and why are they labeled differently?

Life in Two Worlds

"In simple terms, all newts fall under the salamander category, but not every salamander is a newt," explains herpetologist and author Whit Gibbons via email.

Salamanders belong to the amphibian class. Similar to all other amphibians (such as frogs), they possess backbones and hearts with three chambers.

Many defining characteristics are external. Amphibians typically lack scales, for example. They also have diverse respiratory methods. Some species rely on lungs, others utilize gills, and many absorb oxygen directly through their skin. It’s not uncommon for them to use all three methods simultaneously.

The term "amphibian" originates from a Greek word meaning "double life." Except for fully aquatic species, most amphibians split their time between terrestrial and aquatic environments, which explains the name.

Field guides often describe amphibians as "cold-blooded." Unlike mammals, they cannot generate their own body heat or regulate their temperature internally. Instead, they rely on external sources for warmth.

However, "cold-blooded" is merely a colloquial term. In scientific discussions, biologists prefer the more precise term "ectothermic poikilotherms."

The term "newt" is somewhat informal, at least from a scientific perspective.

All in the "Subfamily"

David Wake, a professor of integrative biology at the University of California, Berkeley, serves as the director of the AmphibiaWeb Project, an online database dedicated to amphibians.

"The term 'newt' is specific and derives from the Middle English word newte, a variant of efte," Wake explains in an email. "It lacks scientific significance and is a relic from the Middle Ages," he adds.

Salamanders are categorized into 10 families, one of which is the Salamandridae. Predominantly found in Europe, Salamandrids also inhabit regions of East Asia and northern Africa. In the Western Hemisphere, some species thrive along North America's Pacific Coast, while others are prevalent on the eastern side of the continent.

The Salamandridae family is extensive, containing its own subfamilies. The most prominent is Pleurodelinae, encompassing 109 distinct species.

Traditionally, the term "newt" has been applied to various salamanders within the Pleurodelinae subfamily.

To revisit our earlier question, the eastern newt belongs to the Pleurodelinae subfamily, whereas the red salamander does not.

Gibbons notes that many Eurasian newts, including fire-bellied newts, emperor newts, warty newts, marbled newts, and red-tailed knobby newts, have gained popularity in the pet trade.

North American newt species are less commonly found in local pet stores. Gibbons explains that these New World creatures are called 'newts' instead of 'salamanders' due to the widespread recognition of the term in their native regions.

Lungs and Toxins

Despite their informal classification as a group, newts often exhibit several defining characteristics.

Recall the red salamander (Pseudotriton ruber)? Unlike many salamanders, it does not have lungs. However, newts develop lungs as they mature. Additionally, newts typically have rougher skin compared to most salamanders.

This isn’t a strict rule: Wake notes that salamanders in the genus Pachytriton are referred to as newts, even though they are "fully aquatic and have smooth skin."

"No accounting for taste," Wake remarks.

On the topic of toxicity, Gibbons explains that newts frequently possess "poison glands in their skin, making them mildly or highly toxic to other animals, including humans." A prime example is the Pacific newts of western North America (genus: Taricha).

"Amphibian skin contains a variety of toxins, with tetrodotoxin, the same toxin found in pufferfish, being the most potent," Wake states.

Just how potent is it? Tetrodotoxin (abbreviated as TTX) is over 1,000 times more toxic to humans than cyanide.

A Cold War, Writ Small

Pacific newts rely on tetrodotoxin to deter predators. A single rough-skinned newt (Taricha granulosa) contains enough TTX to kill over 2,000 kingfishers, 200 herons, or even 100 humans!

However, this chemical defense isn’t foolproof. Common garter snakes within the newt’s habitat can consume these toxic creatures and survive. Their resistance to TTX sparked an evolutionary arms race.

Rough-skinned newts are small, slow, and lack physical defenses, making their chemical toxins vital for survival. The emergence of TTX-resistant garter snakes forced natural selection to drive newts to produce even higher levels of toxicity.

In turn, subsequent generations of garter snakes developed even greater resistance to TTX. This escalating battle mirrors a Cold War scenario, with increasingly toxic newts facing off against snakes capable of withstanding extraordinary amounts of TTX.

Increased toxicity led to heightened resistance, and this cycle continued, fueling a biological arms race between the two species that persists to this day. Escalation is a powerful force.