Table of Contents
I like frogs :)
So here’s a whole blog post dedicated to information about them!
What is a Frog? #
Frogs are short-bodied, tailless Amphibia composing the order Anura (from the Ancient Greek: ἀνούρα, meaning without tail). They make up 88% of extant (the opposite of extinct) amphibian species.
The exact characteristics of frogs include a lot of specific details on the spinal structure and the complexion of certain bones, among other things. But mostly, you can recognize frogs by their absence of a tail and their long hind limbs made for jumping.
Frogs vs Toads #
People usually refer to warty frogs as toads. However, the distinction between “frog” and “toad” is not defined, as there is no set rule in taxonomy governing which is which.
There does exist a family of so-called “true-toads”, with species in the family Bufonidae being referred to as such. Over 500 species make up the family of Bufonidae and they are found all over the world, except for parts of Oceania. These animals are in general more warty in appearance, but what sets them apart from the general frog are their parotid glands on the side of their heads. These glands secrete a poison that the true toads use to repel, or even kill predators.
Distribution and Habitat #
Frogs can be found on all continents, excluding Antarctica.
Their habitats vary greatly between different species of frog. Some can be found in aquatic habitats, but others like strolling through sand dunes. Other habitats include rainforests, woodlands and parks or gardens.
Most like it warm and damp, with the highest concentration of frogs being in tropical regions.
Frogs are a mainly carnivorous group, mostly snacking on insects, spiders, worms and slugs. However, there are exceptions to this. There exist some species which go for larger prey, their diet consisting of mice, birds and small reptiles.
Frogs do not drink water!
They rely on their semi-permeable skin to absorb water directly from their surroundings. This feature also allows them to take up oxygen underwater, allowing them to breathe while submerged. Unfortunately, this also makes them very susceptible to pollution, as the frogs absorb pollutants as well which can lead to their death.
Reproduction and Lifecycle #
Frogs lay eggs (groups of which are referred to as frogspawn) which later hatch into tadpoles. Fertilization occurs externally, meaning that the male fertilizes the female’s eggs after they have been released. Per individual mating, frogs can expel between 3'000 and 20'000 eggs.
This process is usually done in water, so as to avoid drying out the eggs.
A few frog species differ in this regard, sometimes laying eggs in soil (in the case of Colostethus machalilla), or carrying the eggs around in pouches (which is how the horned marsupial frog does it).
The monogamous mimic poison frog lies eggs on a plant with the father later carrying the hatched tadpoles to bodies of water.
Two to nine days after fertilization, the tadpoles break the egg barrier and hatch. After hatching, the tadpole’s parents often defend them from predators to ensure their survival.
A tadpole is born with gills and a tail.
Through the tadpole’s process of metamorphosis, it begins to develop lungs, losing its gills in the process, and starts growing legs.
The tadpole’s hind legs start developing before the fore legs.
At the end of metamorphosis, the tadpole loses its tail, absorbing it into its body, and completing its transition into being a frog!
Between the tadpole hatching and its turning into a young frog, around 22 to 25 weeks have passed on average.
The sizes of different frog species are influenced by many factors, mainly their habitat. Tree frogs are generally smaller than aquatic frogs.
On average, frogs are about 6-12cm long and 10-75g in weight.
The largest frogs to have ever lived, that we know of, are the Beelzebufo. Bellzebufo roamed the earth 70 million years ago and measured in at 42.5cm, with an estimated weight of 4.5kg!
The largest living frog species, that we know of, is the Goliath Frog which can grow up to 32cm in length and weigh up to 3.3kg.
The smallest frog species, that we know of, is the Paedophryne Amauensis. This species of frog is about as big as a housefly, measuring 7.7 millimeters, thereby holding the record of being the smallest vertebrate. Its weight is not well documented with measurements ranging from a miniscule 0.7 to 10 milligrams.
This means that the weight of a Goliath Frog is 330'000-4'750'000 times that of the Paedophryne Amauensis!
Frogs heavily rely on their tongues to catch prey. They have the ability to release the tongue from their mouth, grab a victim and retract the tongue in a mere .07 seconds. Prey captured by frogs can experience up to 12Gs of force through this action which is quicker than the blink of an eye.
A frog’s tongue is usually around 1/3 the length of the frog itself. The largest frogs have tongues whose lengths are comparable to our human tongues, measuring at about 30.5cm.
Only recently, in around 2017, have scientists discovered how frogs use their tongues to catch prey. Frog tongues are covered in mucus glands which secrete a unique reversible saliva. This saliva is an incompressible non-Newtonian fluid which can transform from a liquid to a solid and back. Using this property, frogs can shoot out their tongues at prey with their still-liquid saliva which then hardens on retraction, gripping the prey.
In order to swallow their food, the frog has to reliquefy its saliva by closing and retracting its eyes back into its body, increasing the pressure in its mouth. But I like to imagine they are doing this for the same reason we close our eyes when eating a nice slice of cake ^^.
Another key characteristic of most frogs is their protruding eyes. With their eyes, frogs have near 360° vision, allowing them to spot predators and prey from every direction. The protruding eyes also allow them to have their whole body submerged underwater while still keeping an eye on everything that’s going on above the surface.
Frogs may not be able to see well in close distance, but their eyesight excels at making out things afar, especially in low-light conditions. They are able to make out colour, even at night. The eyes of frogs contain two colour-sensitive types of cones (compared to the three humans possess). These cones are only sensitive to green and blue, meaning frogs cannot see red. Frogs additionally cannot differentiate between different shades of green.
In order for the frogs to be able to comfortably see underwater, they have evolved the adaptation of transparent nictitating eyelids. This thin membrane protects the frog’s eyes from debris while swimming underwater.
Frogs can swim, walk, and climb but most importantly, they can jump!
Frogs are the best jumpers, compared to body size, of all vertebrates. The best jumpers among them can jump up to 150 times their own body length.
Some frogs are even able to exert more force than their legs are theoretically capable of. They use a catapult-like mechanism to store and rapidly release elastic energy.
Some frogs have even evolved the ability to glide. The Wallace’s flying frog for example has large feet with loose skin flaps in between its toes. In the air, the frog spreads its toes and stretches these skin flaps to create lift, allowing it to glide. When taken off, the Wallace’s flying frog can glide up to 15 meters.
The communication of frogs is very complex, differing between species or even ponds. Usually, frogs use their vocalizations for communication during mating season or to establish territory. Some species may also communicate through, among other methods, touch, behaviour or movements, such as tapping their toes or waving their arms.
The sounds frogs make range from croaks, over ribbits to trills and other calls. During mating season, female frogs are usually attracted to frogs producing the loudest and longest calls.
Frogs produce sound with the help of vocal sacs.
Sound is produced when the frog closes its nostrils and pushes air from the lung over the vocal cords, through the windpipe into the vocal sac.
These sacs act as a resonance chamber, amplifying sounds.
Since frogs are so-called circular breathers, they can push the air from their vocal sacs back into their lungs and repeat this process. This allows them to croak continuously without having to take a breath.
Frogs are not high up on the food chain. This means they have to get creative with defending themselves against their many predators.
Most probably know about poisonous frogs. They often have beautiful colours to signal their toxicity. These frogs get their poison through either their diet or by secreting it from special glands. The indigenous community used to rub their arrow tips on poisonous frogs’ backs before hunting. This is also where the names for poison arrow frogs or poison dart frogs originate from. However, only three species of frog have been documented to be used for such a purpose. One of which is the golden poison frog, the most toxic of all frog species that we know of.
Some frog species have evolved similar colorations as these highly toxic frogs, but are not poisonous themselves.
The Wolverine Frog (also known as Hairy Frog, Horror Frog or Trichobatrachus Robustus) has an extraordinary way of defending itself. When cornered, this peculiar species of frog breaks the cartilage connection at the near tip of their toe bones. This reveals a sharp bone spur which the frog then forces through its skin through muscle contractions. The frog can then use these claws to defend itself from the predator. It is not fully understood what happens to the frog’s toes after such an encounter, but the claws will retract and torn skin does heal back, meaning the frog can reuse this tactic at a later point.
Other ways frogs defend themselves may include, among other methods, screaming, playing dead, camouflaging and biting.
Frogs in Research #
Now unfortunately this section is not about frogs in labcoats, sorry if I got your hopes up.
Though I did ask DALL-E to generate such an image, I hope you like it!
What this section discusses is the relevance of frogs in research!
From the mid-19th century until the 1980s, frogs have been used to answer many questions in visual neuroscience. They have highly developed vision, a complex retina and display experimentally useful behaviours. However, there is no longer much research being conducted using frog eyes.
Another source of academic interest in frogs stems from their skin. Some frog species produce special antibiotic agents. The mucus frogs produce sometimes contains powerful antimicrobial peptides, but these may be toxic to or quickly disposed of by human bodies, thereby being rendered useless. These mucus secretions are currently being researched and may provide us with insights into alternative ways of fighting drug-resistant bacteria.
Frogs have also been studied in other various fields of science. They have provided insight into physiology, embryology, neuroscience, genetics, behavioural science and much more!
This concludes my blog post about frogs :)
I hope you were able to learn something new!
Thank you so much for reading it all! ❤️
Here are some more pictures that didn’t fit the text but I think you’d enjoy them anyway :)
- True Toad
- Semi-permeable skin
- Distribution and Habitat
- Reproduction and Life Cycle
- Mimic Poison Frog
- Frogs in Research