Cannibal Frogs: Horned Frogs, Darth Vaders & Dragons

Amazonian Front-end Loaders on the job.

By William W. Lamar

Amazon Horned Frog (*Ceratophrys cornuta*) preying on an Amazon Leaf Toad (*Rhinella margaritifera* complex). Image: ©William W. Lamar 2023.

When folks think of frogs, something cute, green, bug-eyed, and friendly comes to mind…

…so something like Kermit.

This is not unreasonable, as many of the little amphibians fit that bill. But beneath those adorable eyes and that placid appearance lurks a mouth that knows few limits. Indeed, were frogs (especially some of those mentioned below) to reach the proportions of, say, medium-sized dogs, they would dispassionately include small children in their menu…and dogs as well, for that matter.

Far from delicate and retiring, frogs can be scrappy. A Scottish folk song, “Frog went a Courtin’” made its first appearance in the 1500s. It spawned–so to speak–many versions, and most involve some weapons and combat on the part of Mr. Frog. Of Germanic and Dutch origin, the Old English “frogga” was a derogatory word first focused on the Dutch. Subsequent pejorative applications, beginning in the 1600s, were directed at the French owing to alliteration and their reputation for consuming frogs’ legs. The ancient term “froggie” means everything from energetic or strong, to powerful and willing to fight. “Froggy” usually refers to all things frog-like. The term “frog” is also applied to hoarseness. Evidently those in need of clearing their throats are presumed to sound like croaking frogs.

What about frogs with other frogs in their throats?

Darth Vader Frog (*Hemiphractus helioi*) engulfing a Snouted Treefrog (*Scinax garbei*) at Orosa, Peru. Image: ©William W. Lamar 2023.

While the majority of these amphibians subsist on a diet of arthropods, some have rather Catholic tastes and come equipped for a more ample form of dining. And the menu may even include brethren and cousins, a practice at least quasi-cannibalistic. How do they accomplish this? Let’s take a look at ingestion in frogs. Whereas our tongues are attached at the rear end, that is, toward our throats, their tongues are just the opposite, with the anchorage being right at the front of the mouth. And frog tongues, while not as long as popular myth depicts them, are large nonetheless, measuring up to a third the length of the owner.

When a frog preys upon something, a lot of sophisticated and athletic things happen in a span of milliseconds. First, the tongue itself, which is not especially sticky in its normal state, secretes a special form of mucous. Then, with blinding speed and accuracy, the frog launches its tongue—using a yo-yo-style, flip-like motion—at the prey. The instant contact is made, that mucous invades all adjacent cracks and crevices and becomes extremely sticky. This causes the prey to remain attached to the extended tongue which is immediately retracted such that the food item is either ingested outright or else held in the grasp of the jaws. The majority of the world’s frog species are toothless. As a group they have gained or lost teeth over twenty times throughout their evolution. The mouth is where ectoderm and endoderm meet, and pointy things often arise there. Some species bear tiny teeth while others possess tooth-like structures called odontodes that function like fangs to pierce and hold prey. For the most part, the actual teeth are small, finely spaced, and do little aside from aiding in retaining whatever is inside the mouth. But oh, those odontodes! They can be so large they must fit into holes in the skull when the frog closes its mouth.

The munchies, literally. Another Amazon Horned Frog snacking on a treefrog (*Dendropsophus* sp.), Yanomono, Loreto, Peru. Image ©William W. Lamar 2023.

A well-fed African Bullfrog (*Pyxicephalus adspersus*) in nature, Limpopo Province, South Africa. Image: ©Gericke 2022. Slightly cropped. Used under Non-Commercial 4.0 International License, Creative Commons.

Some frog species are just built differently. More like tanks or front-end loaders, equipped with enormous mouths, scary odontodes, and enlarged masseter muscles that generate vice-grip power, these guys can handle assorted small vertebrates (usually other frogs) should the opportunity present itself. And of these, several species will willingly bite the hand that feeds them. Just imagine, getting bitten by, of all things, a frog! The African Bullfrog (Pyxicephalus adspersus), at up to four pounds/~two kilos and one of the world’s largest anurans, is designed to live in savanna and other regions known for temporary bodies of water. Not only capable of withstanding severe drought, but also among the most opportunistic of predators, these so-called Pixies devour everything from invertebrates to rodents, birds, and even cobras. As an experiment, a colleague once kept a Pixie in a paper sack in his office for several years. Periodically he filled the sink with water and dumped the frog in. Gradually the dried cuticle secreted by the Pixie for protection would dissolve and the frog would load up on moisture, eat a few meals, and then be returned to the bag. Much bred in captivity for the pet trade, Pixies are long-lived, hardy behemoths that can deliver a painful bite as many a bleeding owner has learned. Just think of the array of formidable wildlife Pixies might face at the water hole; they know how to defend themselves.

In the Chaco region of South America—that includes parts of Bolivia, Paraguay, and Argentina—a similar but smaller counterpart ekes out an existence much like that of Pixies. Characterized by extreme wet and dry seasons, life in the Chaco is rugged. As the rains arrive, Budgett’s Frogs (Lepidobatrachus laevis) emerge. They are nocturnal vacuum cleaners, lying in wait in shallow water and sweeping any creature smaller than they are into their cavernous mouths. When threatened or intimidated, Budgett’s Frogs inflate themselves to ridiculous proportions. If handled, these frogs emit disconcerting screams, hisses, and squeaks and will bite readily. Like that of Pixies, the bony ridges, fang-like odontodes, and jaw strength combine to make this a potentially unpleasant experience.

Argentinean Horned or Pacman Frog (*Ceratophrys ornata*), La Pampa Province, Argentina. One of the most popular exotic frogs in commerce, it is now readily available from captive breeding projects in several countries and are offered in a dizzying variety of color morphs as well as hybrids with other Horned Frog species. Large examples can inflict painful bites when provoked. Image: ©Eduardo Haene 2020. Used under Non-Commercial 4.0 International License, Creative Commons.

My first adviser in graduate school was a cerebral biologist and consummately talented wildlife painter, but he was inept at handling his Pacman Frog (Ceratophrys ornata). The catchy name, a pet industry moniker, derives from a comic arcade game depiction similar to the impression given by these frogs, namely, that of hopping heads and insatiable, gobbling mouths. This corpulent amphibian, a cousin of Budgett’s Frog and hailing from the grasslands of southern Brazil, Uruguay, and Argentina, is now a pet industry mainstay. Indeed, they have been line-bred to produce an array of color morphs and genetically aberrant strains. Living as much as a decade and growing to around six inches in body length, Pacman Frogs are bold, truculent, and ready to consume anything they can cram into their monstrous mouths. This one thrived on a diet of mice. Defending themselves via aggression, they are willing to take on humans, advance toward them, and bite powerfully.

“...they used their data to imagine what extinct frogs such as the gargantuan Beelzebufo ampinga, hailing from the Cretaceous of Madagascar might have delivered. Their conclusion? The bite force is equivalent to that of medium- to large-sized mammalian carnivores!”

Whenever my adviser attempted to remove his frog from its tank for cleaning, the bloody evidence (his) appeared as a dribbled trail across the counter in his lab. Feeling sorry for him, I took over the task, but handling the hefty amphibian always required caution. Upon my approach, the Pacman Frog would flatten out and then quickly inflate, filling the confines of his small terrarium. At that point there was essentially no way to dodge the big mouth, so I would use a minnow net, the kind made for dipping guppies from aquaria. The end result was an extracted frog plus a bent and shredded net.

Impressive!

Colombian Horned Frog (*Ceratophrys calcarata*). Image: ©William W. Lamar 2023.

The so-called horned frogs (genus Ceratophrys) comprise eight species, exclusively South American; all sharing a similar morphology and possessed of a powerful bite. Scientists measured the bite force of Bolivian Ceratophrys cranwelli and extrapolated to gain a picture of what might be delivered from larger congeners such as the Brazilian Horned Frog Ceratophrys aurita. And they used their data to imagine what extinct frogs such as the gargantuan Beelzebufo ampinga, hailing from the Cretaceous of Madagascar, might have delivered. Their conclusion? The bite force is comparable to that of medium- to large-sized mammalian carnivores!

The northernmost member of the genus, the Colombian Horned Frog (Ceratophrys calcarata) is one of the smaller biting frogs. Like its congeners, it is adapted for life in open areas that are seasonally dry. During the 1960s and 1970s, when pet industry importations were wide open and lawless, untold zillions of these tough little frogs came into the U.S. Unfortunately, nothing was known about how to breed them in captivity (or even how to keep them, for that matter), so despite their legendary hardiness, all have passed to the great marsh of The River Styx. At least there they can sing and breed.

Shown above, two boldly-marked color variants of the widespread Amazon Horned Frog (Ceratophrys cornuta) from Peruvian rainforest. Image on left: ©William W. Lamar 2023, image on right: ©Anthony Giardinelli 2023.

*Gulp*. Notice how the “horns” on this frog have folded down over its eyes as Mr. Toad goes down the hatch. Image: ©William W. Lamar 2023.

The Amazon or Surinam Horned Frog, Ceratophrys cornuta, is a larger cousin found to the south. It is a denizen of lowland tropical forests across equatorial South America. As its name implies, this frog (and indeed, most of its congeners) has a horn-like accessory above each eye. When the horned frog closes its eyes, as it does when biting down or swallowing, the appendages bend downward as is shown in the image here. Widespread and locally abundant, these classic sit-and-wait predators spend most of their lives motionless, backed into the leaf litter of rainforests with only the mouth and bulging eyes exposed. Possessed of heads and mouths so large that the rest of the skeleton seems like an afterthought, horned frogs are usually cloaked in mostly somber tones such that they blend perfectly with the dead leaves around them. Roaches, of which thousands of species exist in the tropics along with other arthropods, comprise much of the diet.

But woe betides any passing vertebrate small enough to be ingested.

I’ve spent a lot of time observing these frogs and, at least in the upper Amazon Basin, their favorite meal seems to be Amazon Leaf Toads (Rhinella margaritifera complex). Unsurprisingly, leaf toads secrete potent dermal toxins when they feel themselves being crushed, but these seem to have no effect on horned frogs. Large leaf toads are adorned with bony protrusions and fin-like flanges. Thought to be an aid to camouflage, I wonder whether an additional purpose might be to impede ingestion by Horned Frogs and other small vertebrate predators.

Amazon Leaf Toads (Rhinella margaritifera complex) are a group of at least several closely-related and bizarre-looking amphibians, some of which display elaborate, helmet-like head bosses, together with sawtooth arrangements of tubercles along their sides when mature. Images: William W. Lamar 2023.

Although there isn’t a whole lot of difference between wet and dry seasons in the upper Amazon, the advent of torrential rains creates marshy situations around lagoons in the rainforest, and that is a signal for horned frogs to congregate and breed. Given that finding one under normal conditions is something akin to the proverbial needle in a haystack, the chance to observe a number of them in action is too good to miss.

An adult Black Caiman (*Melanosuchus niger*) on the prowl along the Río Tapiche, Peru. One of the largest extant crocodylian species, mature Black Caimans are apex predators wherever they occur in South America. As is the case with all of the world’s more formidable crocodylians, if you give a big one an opportunity to make a close approach they will likely ruin your day. Image: ©William W. Lamar 2023.

But Amazonian waters tend to be formidably difficult of access. Whether it is mud, slippery slopes, fallen branches and trees, or deep holes, the edges of ponds are really more like hog wallows. One night during a rain, when the horned frogs had congregated and the males were emitting their “BAAA” calls, I ventured out onto a slippery, fallen tree that lay in the marsh and extended right into the midst of the Ceratophrys-fest. Owing to the abundance of grasses I assumed the surrounding water to be shallow. The place was loaded with the corpulent frogs, all intent upon passing on their genes.

Males, their black throats turning gray as they inflated, brayed like sheep. And the females, some of them positively massive, were drawn to the music. Although generally cloaked in somber hues, these frogs are handsome and some are fairly colorful. Rapt by the show and busy admiring the frogs themselves, I failed to realize the grasses were actually a dense floating mass and the water was deeper than I had assumed. This became apparent when the periphery of my headlamp picked up a huge glowing eye far too big to be a frog and far too close for comfort. A large Black Caiman (Melanosuchus niger), likely attracted by the backlit spectacle of a hunched-over and possibly tasty vertebrate (me) crawling along a log, had snuck over for a closer inspection.

OOPS! The show, while a great one, was over and it was definitely time to clear the area; I felt like the club’s bouncer, in this case a large and formidable crocodylian, was showing me the door.

Horned Treefrogs, Darth Vaders & Dragons

Another group of frogs, the weirdest of the weird, also have vice-grip mouths. Some nine species strong (and growing), members of the genus Hemiphractus occur at low- to mid-level elevations in tropical forest from western Panama south into Colombia, Ecuador and across the Amazon Basin. These frogs are usually cloaked in somber hues, the browns, tans, and markings making for excellent camouflage in leaf litter. Nowhere common, and mostly restricted to undisturbed, primary rainforest, these frogs are not only among the world’s most bizarre in appearance, but also have a distinctive way of reproducing. The females develop an adhesive patch on their backs and the eggs are carried there while they undergo direct development. Fully formed little froglets emerge.

The appearance of all species of Horned Treefrogs makes “unique” an understatement; ditto that for “bizarre.” Adorned with sharp angles, bony protrusions, and assorted dermal appendages, some of these uncanny amphibians take on the appearance of Star Wars icon Darth Vader, dragons, or a frustrated Wiley Coyote of Roadrunner cartoon fame. And they are also possessed of yawning, powerful maws…with odontodes. Again, arthropods comprise the bulk of the diet, but Hemiphractus will readily engulf any small vertebrate that happens to pass too closely, but are best known for their predation on other frog species.

“Here be Dragons”. A Sumaco Horned Treefrog (*Hemiphractus proboscideus*) ponders flight at Caucho Caño, Peru. Image: ©William W. Lamar 2023.

One or two species have been successfully bred in captivity, but most life-history aspects surrounding these frogs remain unknown. It took me a long while to get any sort of feel for the kind of habitat where one might expect Hemiphractus to reside; they are overwhelmingly in pristine forest situations, at least in the upper Amazon. And they occur in low densities. I have proof as to where they hide by day, but at night they emerge to perch on low vegetation. Judging by their cryptic colors and patterns, all Amazonian species likely hide in leaf litter on the forest floor, so the common name “Horned Treefrog” is a bit of a misnomer. As you will learn later, captive observation tends to bear this out.

Above left, Hemiphractus scutatus threat-displaying its bright yellow lower jaw and tongue. Right, another example of this cryptically-colored frog species at Alto Yarapa, Peru. Images: ©William W. Lamar 2023.

One, the hulking Hemiphractus scutatus, most definitely does. The only species of Hemiphractus I have ever heard vocalize; it emits a raspy “cro-waahh” on drizzly nights. Looking for all the world like a leaf, when startled the big frog simply flattens out. Like the lid of a trap-door spider’s burrow, it then becomes all but undetectable among the sea of brown leaves in which it lives. By night the orange-red eye is only visible briefly before the frog ducks, so one must fix on the spot and then clamber, like some hokey prank on “Survivor,” through the vegetation in order to search for it. Just once, while pursuing a lizard through the leaf litter by day, I accidentally uncovered a juvenile Hemiphractus scutatus. Otherwise, I have only found this remarkable creature by night, deep in the leaf litter of primary rainforest. Interestingly, it shares the trait with Hemiphractus proboscideus of possessing a saffron-colored tongue. This odd characteristic appears in certain other amphibians and reptiles and the shade is the same. Why, I wonder?

Two examples of the the spectacular Darth Vader/Dragon Frog species, Sumaco Horned Treefrogs (Hemiphractus proboscideus) from Caucho Caño, (left) and Mazán, Peru. Images: ©William W. Lamar 2023.

The latter species found in Colombia, Ecuador, and Peru, is the most bizarre of the bizarre, being adorned with a spiky schnozzle as well as calcar tubercles. So gawky and angular it appears like an animated jumble of bones, this is definitely one of the world’s weirdest frogs. It is so distinctive that the late herpetologist William E. Duellman, when writing his opus on the reptiles and amphibians of Santa Cecilia, Ecuador, and dealing with Hemiphractus proboscideus, briefly abandoned the staid academic tones for this comment, “…any damn fool can identify this frog.” By night the ones I have encountered are down low, just above the leaf litter. Once, during a late-night cold rain, I found a specimen hunkered at the tip of an eight-foot vertical, leafless stem. It looked as miserable as I felt. When startled the frog will either dive into the leaf litter or else gape, revealing the yellow tongue. If that fails, a bite may follow. I have never been bitten by any of the frogs in this article. Reason? Mostly luck, but aside from not being eager to give blood, I also worry that their power might exceed the resistance of their mandibles. In other words, they might break their own jaws while biting me.

Again, two distinct color forms of Hemiphractus helio at Callao on the Río Tapiche (left), and Caucho Caño, Peru (right), illustrating why these rarely-observed frogs have been christened “Darth Vader Frogs” by some regional herpetologists. Images: ©William W. Lamar 2023.

*Hemiphractus proboscidea* feeds on a lizard (*Anolis fuscoauratus*). Image ©William W. Lamar 2023.

Hemiphractus helioi, the one remaining member of the genus found in Amazonian lowlands, lacks the distinctive yellow tongue (Why is that?) but otherwise seems to occupy the same habitat. In fact, I have found both this frog and H. proboscideus in the same small patch of rainforest. Perhaps owing to size difference (H. helioi is larger and more robust) they are able to partition the resources. One night in Brazil, just across the Río Yavarí from Peru, I came across an adult H. helioi being attacked by a strange and quite beautiful rodent. Things happened quickly once my flashlight had exposed them so I only got a fleeting look at the slender rodent, but it appeared to be black and white, and not especially large. It made a swipe or two and the frog’s snout and was met with open jaws. It ran off before I could ascertain any more but I have never seen an Amazonian mammal remotely similar. The frog made it through with a scratch or two.

A *Hemiphractus helioi* found in nature as it captured a rainfrog (*Pristimantis carvalhoi*). The very sharp pair of fang-like odontodes are visible in the center of its jaw. Image: ©William W. Lamar 2023.

Only once have I ever come across a Hemiphractus in the act of feeding and it was an H. helioi that had captured a small rainfrog called Pristimantis carvalhoi. Immediately I lay down in the leaf litter and snapped shots of the encounter. Later I hatched a plan that has worked nicely where Hemiphractus or Ceratophrys are concerned. I took a sturdy cardboard box and slit the corners such that the sides could quietly be un-taped and lowered. Then I set up a leaf-litter base and released a frog into the enclosure. Once the tenant had settled I introduced potential prey and let nature take its course. When a frog grabbed its prey I lowered a side and eased in with the camera, gently removing any obstructing leaves. Aside from the photographic opportunities an advantage to this was in observing the way the frogs settled in. Ceratophrys, for instance, would invariably back into the leaves with only the face showing. Hemiphractus tended to seek stacks of leaves with space between them and hole up between the layers.

Artifacts of captivity?

Possibly; but the speed with which they did this leads me to believe it is something that occurs in nature. At the very least it had all the hallmarks of natural behavior.

If you’re fortunate enough to see any of these extraordinary frogs in the wild, you’ll find the experience unforgettable.