Five Fantastically Freaky Frogs

Amazing Adaptations

Image Source: Rushenb

Welcome back to The Nature Nook for our first post of 2021! We hope everyone has had a great Christmas and New Year and is ready to delve into our next Freaky Frog article! So far in this series, we’ve looked at a frog the size of a baked bean, a frog whose unsightly folds of wrinkled skin has earned it the name ‘scrotum frog’, a frog that can protrude its own bones from its toepads, and a frog that freezes solid and defrosts with the changing of the seasons. All very strange adaptations, I’m sure you’ll agree. Next time, Freaky Frogs will be heading in a new direction, looking at the truly bizarre ways in which some species reproduce and take care of their young – but not before we take a look at five new fantastic frogs and their amazing adaptations.

1. Pebble Toad

Most amphibians have soft bodies, thin skin, and no obvious claws, spines, or defensive armour. To put it another way, they seem quite helpless. Nevertheless, many amphibians have developed various defence mechanisms to keep themselves alive, ranging from slippery skin to toxic secretions – although some species have been a bit more inventive…

The pebble toad is found only on two moist table-top mountains in Venezuela called ‘tepuis’. The sheer vertical sides of these huge rectangular plateaus rise precipitously above the misty cloud forests below. They are so tall and inaccessible that they each have their own climate and ecosystems, supporting endemic species that are found nowhere else in the world. They have become high-rise ‘islands’.

A pebble toad
On the tepuis of South America, species have followed independent evolutionary pathways, so there are often unique spiders, scorpions, amphibians and carnivorous plants on each of these bizarre mountains. The pebble toad lives on just two tepuis, but some of its close relatives can be found on others in the region.
Image Source: Gérard Vigo

Barely an inch long, the pebble toad is prey for a variety of creatures, including large insects and tarantulas. Its colouration allows it to blend in quite well with the rocky, uneven terrain of its environment – but what happens if its disguise is rumbled? Well, it doesn’t have toxic secretions or any other obvious defences, and it can’t even hop or swim very well. So, if a predator comes too close, it does something rather extraordinary. It simply folds its limbs under its body, tucks its head in, and tenses its muscles so that it becomes rigid. If it’s on an incline, this causes the little amphibian to roll down the slope, looking like a dislodged pebble.

This may seem like an extreme and desperate act, but it allows the pebble toad to make a very quick getaway, and its tiny body weighs so little that the impact of the fall is too minor to cause any real injury. It bounces down the rocky walls like a rubber ball until it finally reaches a flat surface. Then, it simply gets up and ambles away, none too worse for wear.

Like many others, I first learned about the pebble toad in the 2009 BBC wildlife documentary Life (narrated by Sir David Attenborough, of course), and the sequence in which it features is still just as amazing today as it was over ten years ago.

2. Paradoxical Frog

The paradoxical frog is so-called because its tadpoles are significantly larger than the adult frogs they will turn into. This highly aquatic amphibian from South America spawns in floating foam nests. The eggs contain a large amount of yolk, which can sustain the developing tadpoles for weeks, allowing them to reach up to 25 cm in length – the largest of any frog. During metamorphosis, however, the tail is absorbed and the body, including its vital organs, shrinks into a frog a mere third of the tadpole’s maximum length.

Museum models of a paradoxical frog and its tadpole, showcasing the obvious size differences between the two
These models of the paradoxical frog from the Natural History Museum in London show the size of the full-grown tadpole and the adult frog for comparison.
Image Source: Chipmunkdavis

3. Glass Frog

There are no prizes for guessing how glass frogs got their name! From above, most species looks fairly ordinary, with standard lime-green skin, including the cricket glass frog in the image below.

A cricket glass frog
Glass frogs, which are common in South America’s humid cloud forests, lay their eggs on leaves overhanging streams. When the tadpoles hatch, they drop into the water below to continue their development.
Image Source: Brian Gratwicke

On their undersides, however, these amphibians have extremely thin, see-through skin. In some species, this underbelly skin can be almost disconcertingly transparent. Blood vessels, bones, the digestive tract, and other organs – even the beating heart itself – can clearly be seen. These frogs leave nothing to the imagination.

A glass frog viewed from beneath, showcasing its transparent skin and internal organs
When viewed from underneath, the blood vessels, internal organs, and even the green bones of this powdered glass frog are visible.
Image Source: Geoff Gallice

But while this is certainly one of the most amazing adaptations in the amphibian world, what is its purpose? After all, the transparent area of these frogs is always facing the ground, and even if viewed from below, it just seems to put their full internal anatomy on display. Well, glass frogs spend a lot of their time sitting on large rainforest leaves. This means that the green colouration of the frogs’ upperparts provides camouflage from anything looking down on them. And when illuminated from above, with light shining through the leaf, their transparent undersides are thought to make their silhouettes less obvious to any potential predators below.

4. Flying Frog

Powered flight in the natural world has evolved four times. Today, most birds, insects and bats can take to the air whenever they please. And in the past, during the time of the dinosaurs, now-extinct reptiles called pterosaurs soared across prehistoric skies. But points should still be awarded to a few other animals for trying. There are flying squirrels, flying ‘lemurs’, flying mice and flying lizards, to name a few. None of these animals, despite what their names may suggest, can truly fly, although they are able to glide long distances using specialised flaps of skin.

Some frogs are also capable of this. Perhaps the most well-known is Wallace’s flying frog, which lives in the rainforests of Southeast Asia, leaping and gliding from one tree to another. It is named after Alfred Russell Wallace, the English naturalist who developed the theory of evolution at roughly the same time as Charles Darwin. Wallace became aware of this frog and its remarkable adaptation while he was exploring Borneo; a worker brought him a specimen, insisting that he had seen it glide down from a tree in a slanting direction. Because Wallace was the first scientist to report on and study this species, it was later given his name.

A Wallace's flying frog sitting on bamboo
During the rainy season, a female Wallace’s flying frog lays her eggs inside a foam nest, which she whips up on a branch using secretions of mucus. When the tadpoles hatch, they fall into a pond below.
Image Source: Rushenb

When threatened or searching for prey, Wallace’s flying frog leaps from a branch and spread its four limbs. The webbed feet used by the frog’s ancestors to swim faster have been enlarged and repurposed as mini parachutes, catching the air as it falls. These splayed feet, along with a fringe of skin stretching between its limbs, allow this frog to glide up to 15 m to a neighbouring tree.

5. Moustache Toad

Moustaches seem to divide women. Some like them; others hate them. But for a species of frog called Leptobrachium boringii, otherwise known as the Emei moustache toad, it turns out that all females like them. In fact, the males specifically grow them during the breeding season to impress potential mates.

Okay, we admit: they aren’t real moustaches. In fact, they aren’t even made up of hair. They’re actually sharp ‘nuptial spines’ growing on the upper lip. The males (which, unusually for frogs, are larger than the females) headbutt one another underwater, attempting to drive their sharp moustache spines into the bellies of their opponents. Despite receiving several puncture wounds during these bouts, males are rarely mortally injured. Females later arrive to lay their eggs, and the strongest male with the biggest and most impressive moustache, having seen off all his rivals, gets to fertilise them.

A male Emei moustache frog with nuptial spines on his upper lip
At the height of the breeding season, the nuptial spines on the upper lip of male Emei moustache frogs are clearly visible. They are lost at the end of the season.
Image Source: Cameron M. Hudson & Jinzhong Fu

The moustache frog uses its amazing adaptations to procure a mate. And that is where our Freaky Frogs series will be heading next – into the bizarre breeding behaviour of this incredible group of amphibians. First up – Darwin’s frog, a species where the male dutifully looks after his tadpoles… inside his own vocal sac.

Author

  • With a background in conservation and animal behaviour studies, Jason's passion lies in the natural world. He adores all things nature and enjoys nothing more than spotting rare and interesting species out in the wild. He has also worked in a zoo and knows plenty about keeping the animals inside our homes healthy and happy, too.

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