Deepa is a freelance researcher and journalist. She writes and makes documentaries and videos.
The Evolutionary Leap From Water to Land
Nature is full of connections, the bridges of evolution making possible different inhabitable ecosystems for different sets of species. The world is throbbing and teeming with life and is, one might say, a bit crowded.
Diversity is nature’s primary achievement. The planet abounds in thousands of different life forms and a variety of different families and species within each category of them. Among these, frogs and toads represent the most intriguing link of evolution, the bridge between two distinct groups of organisms, the one that inhabits water and the one treading on land.
They are the first vertebrates to leave the water and migrate to terra firma. Frogs seated on their Colocasia and lotus leaf thrones, swinging in wind, catching flies in an acrobatic swing of their swift and long tongue, are the subjects of stories in which they predict rain and even wed princesses.
Frogs are different from toads in plenty of ways, though it is only normal to mistake one for the other. For instance, the skin of a frog is slimy and smooth while a toad has rough skin with protuberances all over. Additionally, toads can live under dry conditions and have shorter legs than frogs, and—compared to frogs— toads are heavy-set and stubby. Furthermore, the spawn of frogs is seen as a fizzy lump in water whereas toad spawn looks like long floating strings.
Imagine that a family of amphibians with 6,000 species of frogs and toads were the first inheritors of this landmass that we call Earth, our home! In our material perception of land as wealth to be amassed, we conveniently ignore the claims that other species have to the very same land. If any one of those species were to raise an irrefutable claim, that would be frogs, being the first ones to set foot on the land. About 90% of all amphibians belong to the two categories, frogs and toads.
Naturalists and biologists still continue to discover new frog species hidden within the rich flora and fauna of our planet. There are no toads in Antarctica, although all other continents have them. Actually, frogs used to live in Antarctica many millions of years ago, as fossil evidence suggests. The decreasing humidity of that continent caused the frogs and toads to go extinct.
Madagascar is the frog capital of the world, home to around 500 frog species. The largest frog is the Goliath frog, which is endemic to West Africa and weighs in at around 4kg, with a snout-to-back-end length of 300 millimeters.
A Frog’s Croak
Do you know that there is no correlation between the size of a frog and the loudness of its croak? Frogs are such elusive and diverse creatures that a 3cm-sized member of this group makes a sound that can be heard over a 500-meter distance. Just try shining a torch into the face of a frog. Its croaking comes to a sudden halt. It freezes, unable even to move. Now, if you turn off the torch and wait for some time, the croaking will resume as nothing happened.
Variations in the croaking sound are as diverse as the species's diversity. Jerdon’s narrow-mouthed frog (Ramanella Montana) makes a sound similar to ‘brong, brong.’ Microhyla ornate, or the ornate narrow-mouthed toad, is loud and makes a ‘drong, drong’ sound. Bush frogs, found in Asian and Sub-Saharan Africa are unique in their histrionic abilities as they sound like a ticking clock – ‘tik, tik, tik.’ These frogs possess single and double vocal sacs. Common toads have single vocal sacs while bullfrogs have double vocal sacs.
They can croak on land as well as underwater with equal ease because of the special nature of how the sound is made. The croaking sound is made by closing both the mouth and the nostrils and passing air back and forth from the mouth to the lungs through the vocal cords. Hence, the frogs croaking underwater do not need to worry about water entering their lungs and drowning. When startled, there is another sound that a frog makes – a kind of squeal that is shrill and made by keeping its mouth wide open.
What Habitat Do Frogs Like?
Frogs live in bushes, thickets, grasslands, rocky terrains, small water bodies, etc. The tropical regions have an abundance of them. Their skin has two layers, but unlike fish, the outer layer is covered by a thin layer of dead cells, enabling the frog to live on land.
The mucous glands in the skin also secrete a fluid that keeps the skin moist and this is what makes frogs slimy to touch. Tree frogs have a special kind of mucous gland under their feet which releases a sticky fluid to help them climb. Some frogs, mostly terrestrial ones, have poison glands that secrete a poisonous milky liquid when they are frightened.
Most species of frogs breed in water. A frog's/toad's average lifespan is about 10-15 years, but some toads such as European Common Toad are reported to have lived up to 40 years.
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Can Frogs Change Their Skin Color?
Many frogs can change their skin color just like chameleons. Chromatophores in their skin are the secret behind this ability. European tree frogs can change colors within a range of pure white to dark green. There are sometimes quite distinct color differences between the male and female of the same frog species. Bullfrog males have yellow bodies and blue sacs while females don brown bodies and green vocal sacs.
Like many other species on the planet, some frog species also imitate other unrelated species in shape and color. The fungoid frog is one such curious creation of nature that looks like a fungus named, orange-red fungus. Melanobatrachus Indicus is an Indian frog that is coal black in color.
What's in a Frog's Diet?
Tadpoles are foodies and carnivores. They feed on earthworms, certain varieties of fish, and even dead tadpoles. It takes about 40-45 days for the tadpoles to develop their hind legs. In 55-60 days, they will also have full-grown front legs.
Soon, they will start exploring the dry land and soon the end of a protruding tail will disappear. Irrespective of the color of the frog species, all the tadpoles are brown, a camouflaging technique devised by nature to protect them from predators.
Adult frogs and toads generally feed on insects, worms, spiders, and even slugs. Some kinds are known to even eat larger prey such as mice, birds, and small reptiles.
How a Frog's Tongue Works
A frog’s most important feeding tool is its tongue. The fairy tale image of a frog catching a fly by throwing out its tongue in a sudden death blow has a lot of scientific explanation to do behind it. The tongue of a frog has sophisticated muscles and the tongue is attached to the front part of the mouth. The rest of the tongue is folded back into the mouth’s inner cavity. The saliva in the mouth keeps the tongue sticky.
Whenever a prey is near, the frog can, in a split second’s time, flick its tongue out and catch it. This is possible on land alone but in water, the tongue is literally useless, which is why some water-exclusive frogs have lost their tongue entirely through genetic evolution.
Slow-Motion Footage of Frogs Capturing Prey
How Human Activities Affect Frogs and Toads
About one-third of the planet’s frog species are on the edge of extinction. The Lake Titicaca Giant frog used in traditional medicine is on the verge of disappearing from Earth’s face, thanks to mining pollution. In countries such as Peru, many endangered species of frogs and toads get pulped into ‘frog smoothies’ (a popular delicacy, on a daily basis) in street eateries. The belief that this frog drink is beneficial to health, though unproven, prevails.
In the UK, climate change and warmer temperatures are causing fatal viral diseases in amphibians living in ponds, pushing them towards extinction. Another alarmingly strange phenomenon is the widely used pesticide atrazine, which, when applied to fields, turns male frogs into females.
A 2010 study conducted at the University of California, Berkeley, brought this to the world’s attention. When these sex-changed females mate with other males, the entire offspring are male because the females in this case have no female genetic composition. The imbalance of male-female sex ratios will eventually lead to the extinction of the species.
In 2021, the evidence conclusively showed that along with the Ivory-billed Woodpecker, Spix’s Macaw, Smooth Handfish, and Jalpa False Brook Salamander, the Du Toit’s torrent frog has bid goodbye to earth. Intensive logging and agriculture drastically changed the frog's habitat, and are likely culprits in the frog's extinction.
There are many stunningly beautiful frogs that stand out for their color mostly. The Red-Eyed Tree frog in its green attire, the glass frog with its translucent body, the Amazon Milk frog with the variegated brown and brown-white stripes, the green, brown, and black striped Pacman frog, the Blue Poison Dart frog in its dotted deep blue coat, and the lemon yellow-toned Golden Poison frog are all breathtakingly gorgeous.
There are burrowing frogs, Tomopterna Breviceps, and they burrow soft and sandy soil during nights with the help of their shovel-shaped back legs. They also spend months and even years inside these burrows, completely buried in the soil during the dry season, and only come out when it finally rains. Their body is a water reservoir that keeps them alive during this hibernation. A burrowing frog can store water up to 50% of its body weight.
The Malabar gliding frogs are endemic to the Western Ghats in South India. They are bright green in color and their toes can fan out as they are webbed together. With this super-convenient adaptation, they glide through the air, making the onlooker think that they are actually flying. They can literally fly from a higher perch to a lower one and glide horizontally to some distance.
The bright red color of the web on its feet has another advantage – it frightens off the predators. When the toes are held together and the frog is sitting, the red web folds between them and totally disappears.
Frogs and Toads in Culture
Ever since proverbs such as ‘the frog in a well’ became part of our semantics, since the days when Aesop told frog fables and the Brothers Grimm wrote about the Frog Prince, frog stories have abounded in human history and culture. In Japanese culture, the frog is viewed as the animal of luck and cleansing and this is why Feng Shui, the spiritual practice of connecting spaces to energy flows, uses frog statuettes as symbols of prosperity.
There are many people who are afraid of frogs and toads as they might be of lizards, cockroaches, spiders, and other insects that occasionally invade the security of their homes. There is a specific name for the fear of frogs – "ranidaphobia." Many cultures believe the frog croaks to bring rain, the fact being frogs sense an incoming change in weather.
They also play an important role in the food chain by eating algae and preventing algal blooms that are a threat to the aquatic ecosystem; by becoming a source of food for birds, snakes, and certain fish; and by eating and thereby controlling the insect population.
Humans should especially thank frogs as they have been the experimental animals for us to learn anatomy, test new medicines, and save lives.
African Clawed Frog Was Once Used as a Pregnancy Test
References and Further Reading
- The Country That Blends Endangered Frogs | BBC News
Peru's diverse wildlife makes it a hotspot for the illegal trade in live animals – and the country's ecological police are struggling to cope.
- Climate Change: How Frogs Could Vanish From Ponds | BBC News
Climate change is having an impact on British wildlife, say scientists mapping a deadly frog disease.
- Pesticide Atrazine Can Turn Male Frogs Into Females | Berkeley News
Atrazine, one of the world’s most widely used pesticides, wreaks havoc with the sex lives of adult male frogs, emasculating three-quarters of them and turning one in 10 into females, according to a new study by UC Berkeley biologists.
- Why Frogs Need Saving | Phys.org
In honor of the world's largest day of amphibian education and conservation, biologist Maureen Donnelly offers insight on why frogs are important and in need of saving. The herpetologist has studied amphibians and reptiles for decades.
- Yearender 2021: 5 Species That Went Extinct This Year
Climate change has been making a radical impact on the planet with every year, a host of species vanishing from the earth. This year too, we lost a few. Here's a list.
- The World's Most Endangered Frogs | Nature – PBS
Meet the frogs on the brink of extinction.
- Frog and Toad | San Diego Zoo Animals & Plants
The world holds a wonderful variety of frog species, each adapted to living in its unique habitat, be it cool mountain slopes, scorching deserts, or tropical rainforests. Depending on the species, they may be found in water, on land, or in trees.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
© 2021 Deepa