11 Colorful Facts About the Red-Eyed Tree Frog

Agalychnis callidryas, better known as the red-eyed tree frog, is one charming amphibian. With bright red eyes, colorful sides, and an extremely expressive face, it’s hard not to be captivated by this wonderful frog. But no animal should be defined by good looks alone—so we talked to Don Boyer, Curator of Herpetology at the Bronx Zoo, to find out more. 

1. They've been around for millions of years.

Frogs, in general, are a pretty old bunch. Fossils show that frogs have been around for hundreds of millions of years; red-eyed tree frogs specifically emerged roughly 10 million years ago. 

2. Red-eyed tree frogs are masters of disguise. 

These amphibians are arboreal, meaning they spend a lot of time hiding in the trees. The frogs live in tropical lowlands in Central America and northern South America, and though one might think that its bright red eyes and blue and yellow markings would put the amphibian in danger, the crafty frog actually uses its flashy colors to its advantage. 

When seated on a leaf, the red-eyed tree frog tucks its legs in close to its body and closes its eyes to hide—but when they sense a predator, they open their eyes and jump away, exposing a whole slew of dazzling colors. Some scientists believe that this sudden burst of color can startle animals and throw them off guard, but a more popular theory is that it helps the animal get back into hiding. "If you startle a white tailed deer, the first thing it does is flip up its bright white [tail] and you see that, but as soon as it stops running, the tail drops back down and it blends in with the surrounding environment," Boyle explains. "As a predator, you’re looking for that bright blue/yellow contrasting coloration, [but] now that the frog has landed and it just looks like a big green blob on a leaf, you may not detect it." 

3. Night is the best time to spot them. 

During the day, the red-eyed tree frog hides its colors and sleeps stuck under leaves, where it blends into the foliage perfectly—sometimes, the frog will even have tiny yellow spots that resemble leaf blemishes. 

“We have an exhibit of them at the [Bronx] zoo and sometimes—right in front of people—they’re sitting on a leaf and they’re just tucked up sleeping, and people are like ‘well there’s nothing in here,’ or 'I don't see anything,'” Boyer says. “And you’re like ‘well there’s a frog about a foot from your head!’” 

At night, when they're less at risk of becoming a meal, the frogs are much more active; they spend the time hunting for insects. 

4. They’re somewhat poisonous. 

Tree frogs rely more heavily on their camouflage for protection, but they do have some toxins in their skin. This poison isn't exactly dangerous, but it does leave a bad taste in some predators’ mouths. “I don’t think there’s animals that necessarily would die from eating them, but I think some species probably don’t eat them because they don’t taste the best,” Boyer says. 

5. A special trick helps them eat faster. 

If you've ever seen a frog eat something, you might have noticed they close their eyes. Like most frogs, red-eyed tree frogs use their eyes to help swallow. Their tiny teeth hold the insect in place, and they retract their eyes into their body to push the meal down their throats. While they can swallow without the extra push from the eyes, it helps expedite the process so they can get moving. 

6. Male tree frogs use vibrations to ward off competition. 

When marking territory, males will shake their perch violently. The vibrations tell other males that the area has already been reserved. Scientists used a miniature seismograph to verify that the shaking branches were due to the frogs’ movements and not the wind. The vibrations travel about 1.5 meters, giving the male frogs a good amount of personal space. 

7. Mating season is like a big singles bar.

Mating season generally lasts from fall to early spring. Males climb down from their trees and gather around bodies of water; once each finds the perfect location, he'll start calling, at which point the females will descend from the trees and respond to the calls. “The breeding aggregations are pretty impressive,” Boyer says. “I’ve seen breeding aggregations of red-eyed tree frogs in Costa Rica and you can have literally hundreds of frogs around a body of water.” 

8. Females take the males for a ride. 

Once the female has selected her mate (it’s unclear what the deciding factors are, but it’s likely a mixture of size and call), the pair will go into amplexis: the female will carry the male around on her back for the course of the egg laying process. After the male hops on, the female draws in water that she uses to lay her gel-like eggs. After she lays her eggs on the bottom of a leaf, the male fertilizes them externally. 

“You can almost guarantee the eggs you fertilize will be your offspring unless another male wrestles you off—and some clutches do have multiple sires,” Boyer says. “But the idea here is that if you’re male, you can go into amplexis with a female and you can try to ensure that those eggs laid will be your eggs.” 

9. Tadpoles can hatch early.

Red-eyed tree frog eggs are laid under leaves that loom over water, so that when the eggs hatch, the tadpoles can fall directly in. These frogs-to-be generally hatch about a week after being laid, but they can emerge sooner, after just four or five days, if their survival depends on it. Because some species of snakes and wasps like to dine on the jelly-like eggs, the tadpoles are equipped with a special defense plan: If they detect movement or vibrations, they hatch prematurely and make their escape. 

10. It takes a while for them to grow up. 

It takes a red-eyed tree frog one to two years to reach maturity, depending on how much they eat. The frogs are usually about 1.5 to 2 inches long, and females are always larger than the males (a necessity for giving those piggyback rides). The frogs usually survive about 5 years in the wild, but can live much longer in captivity. 

11. Scaling wet leaves is no problem.  

These crafty amphibians can defy gravity and cling to leaves, sticks, and even glass. Frogs’ feet are not entirely flat: If you look at them under a microscope, you would see hexagonal nanopillars, which, Boyer says, “stick out [and] fit into irregular surfaces very well.”

In between each pillar, there are channels that allow mucus to flow. This gives the feet a wet adhesion. Using both friction and that adhesion, these frogs can stick to almost any surface—especially anything moist. 

All images courtesy of iStock unless otherwise stated. 

Watch How a Bioluminescence Expert Catches a Giant Squid

Giant squid have been the object of fascination for millennia; they may have even provided the origin for the legendary Nordic sea monsters known as the Kraken. But no one had captured them in their natural environment on video until 2012, when marine biologist and bioluminescence expert Edith Widder snagged the first-ever images off Japan's Ogasawara Islands [PDF]. Widder figured out that previous dives—which tended to bring down a ton of gear and bright lights—were scaring all the creatures away. (Slate compares it to "the equivalent of coming into a darkened theater and shining a spotlight at the audience.")

In this clip from BBC Earth Unplugged, Widder explains how the innovative camera-and-lure combo she devised, known as the Eye-in-the-Sea, finally accomplished the job by using red lights (which most deep-sea creatures can't see) and an electronic jellyfish (called the e-jelly) with a flashy light show just right to lure in predators like Architeuthis dux. "I've tried a bunch of different things over the years to try to be able to talk to the animals," Widder says in the video, "and with the e-jelly, I feel like I'm finally making some progress."

[h/t The Kid Should See This]

Big Questions
Why Are There No Snakes in Ireland?

Legend tells of St. Patrick using the power of his faith to drive all of Ireland’s snakes into the sea. It’s an impressive image, but there’s no way it could have happened.

There never were any snakes in Ireland, partly for the same reason that there are no snakes in Hawaii, Iceland, New Zealand, Greenland, or Antarctica: the Emerald Isle is, well, an island.

Eightofnine via Wikimedia Commons // Public Domain

Once upon a time, Ireland was connected to a larger landmass. But that time was an ice age that kept the land far too chilly for cold-blooded reptiles. As the ice age ended around 10,000 years ago, glaciers melted, pouring even more cold water into the now-impassable expanse between Ireland and its neighbors.

Other animals, like wild boars, lynx, and brown bears, managed to make it across—as did a single reptile: the common lizard. Snakes, however, missed their chance.

The country’s serpent-free reputation has, somewhat perversely, turned snake ownership into a status symbol. There have been numerous reports of large pet snakes escaping or being released. As of yet, no species has managed to take hold in the wild—a small miracle in itself.

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