Cool Frog Facts
How many amphibian species are there?
There are 6,317 amphibian species, of which 5,576 are anurans (frogs and toads), 566 are caudates (newts and salamanders), and 175 are gymnophiones (caecilians).
What's a caecilian?
Caecilians are amphibians that lack limbs. They look a bit like earthworms or snakes and can grow up to 1.5 m (5 ft) in length. As they generally live underground, they are the most under-studied group of amphibians.
Do all amphibian species have tadpoles?
No. Some caecilians give birth to live young and some salamanders have larvae that essentially resemble the adult stage, but with external gills. There are many terrestrial frog species that emerge as froglets directly from the egg, bypassing the tadpole stage altogether. This adaptation allows them to live far from water bodies (on mountain tops for instance), and provides the parents with an increased ability to guard their eggs, which are laid on land. It also removes a serious risk that aquatic larvae must face: predation by fish or dragonfly larvae. Many terrestrial salamanders employ this strategy as well. (Photo credit unknown).
How long have amphibians been around?
Amphibians are the oldest land vertebrates. Ichthyostega was an amphibian species that lived in Greenland 362 million years ago.
Gastric brooders
The Northern & Southern Gastric Brooding frogs Rheobatrachus vitellinus and R. silus lived in eastern Australia. These amazing frogs could actually shut down their gastric juices while rearing their young inside their stomachs! They therefore held great promise for advances in human medicine, as research on these frogs may have resulted in a cure for ulcers.
Unfortunately, the gastric-brooding frogs vanished within a few years of being discovered by scientists--the health of humans and frogs is clearly intertwined. On the right you can see a tiny R. silus froglet emerging from its mother's mouth. (Photo by D. Sarille; top photo of R. vitellinus is by M. Davies)
Smallest frog
The smallest frogs are the Brazilian Gold Frog Psyllophryne didactyla and the Cuban frog Eleutherodactylus iberia. These frogs measure only 10 mm (0.6 in) when fully grown. (Photo of E. iberia by M. Lammertink)
Largest frog
The world's largest frog is the Goliath Frog Conraua goliath, which lives in western Africa. They can grow to be over 30 cm (1 ft) long, and weigh over 3 kg (6.6 lbs). This species is endangered, due to conversion of rainforests into farmland, and due to their being used as a local food source.
Strawberry poison-dart frog eggs for breakfast?
The strawberry poison dart frog Dendrobates pumilio has an extraordinary reproductive strategy. Females lay their eggs in the leaf-litter or on plants. When the tadpoles hatch, they climb onto the mother's back. She then transports them to small pockets of water in bromeliads or other vegetation, often high in the trees. She returns intermittently through their development to lay unfertilized eggs in the water. These eggs serve as the tadpoles' primary food source. Dendrobates pumilio occurs throughout the Caribbean coast of Central America. Other poison-dart frog species carry their tadpoles around as well. Note the tadpoles in the photo to the right. (Top photo of D. pumilio taken at Red Frog Beach, Bocas del Toro, Panama. Bottom photo is of an unknown species on Costa Rica's Osa Peninsula. Both photos by K. Kriger)
Marsupial frogs
Assa darlingtoni, commonly called the marsupial frog, lives in the rainforests of eastern Australia, where it lays its eggs in moist leaf-litter. Both parents guard the nest of about 30 eggs, and when the froglets emerge, they crawl into the father's two hip-pockets, where they hang out for several weeks. The adult in the picture is about the size of a thumbnail, imagine how small the froglets are! (Photo by K. Kriger)
What does amphibian mean?
The word amphibian is derived from Greek and means 'two lives', referring to the fact that most amphibians spend their larval stage as aquatic, herbivorous tadpole, and their adult stage as terrestrial carnivore. However, some amphibians spend virtually their entire lives in the water (i.e. African clawed frogs Xenopus laevis, and mudpuppies Necturus). Others, like the Puerto Rican coqui Eleutherodactylus coqui or Dunn's salamander Plethodon dunni from Oregon, spend their entire lives on land: they lay their eggs in moist leaf-litter, bypass the tadpole stage and may never enter a water body. (Photo of Whistling Treefrog Litoria verreauxii by K. Kriger)
How do amphibians breathe?
Tadpoles have gills like fish, and most adult frogs have lungs like yours. However, amphibians have permeable skin that allows them to absorb both water and oxygen directly from the environment, right through their skin. Plethodontid salamanders have no lungs: they breathe solely through their skin and through the tissues lining their mouths. The world's first known lungless frog, Barbourula kalimantanensis, was recently found in the jungles of Borneo. The largest lungless tetrapod (a tetrapod is a 4-legged animal such as an amphibian, reptile, bird, or mammal like yourself) is an 80 cm (2.5 ft) caecilian Atretochoana eiselti from Brazil. (Photo believed to be by D. Bickford)
Thought only birds built nests?
The Australian stony creek frogs Litoria wilcoxii and Litoria jungguy occasionally build a sand nest for their eggs. In the photo at right, eggs are in the center of the nest, which is immediately beside a stream. Thus the eggs are kept in a moist environment, safe from fish for the time being. The next large rain will wash them into the stream and they will emerge as tadpoles. (Photo by K. Kriger)
What's the difference between a frog and toad?
Not much. True toads (bufonids) tend to have short legs and dry 'warty' skin, though there are plenty of frog species that fit this description as well. Toads tend to have toxic secretions, but so do poison dart frogs. However, toads do have significantly higher chances of resembling that alien who lives down the street from you. (Photo of American toad Bufo americanus, our national toad, by K. Kriger)
What are the big warts behind a toad's eyes?
Those are the paratoid glands, which hold a cocktail of toxic secretions. Since toads are pretty slow they need to defend themselves from predators. The cane toad Bufo marinus has 20 bufotoxins, some of which are potent enough to kill a snake many times its size. Contrary to urban legend, if you lick one, you'll probably just throw up. The Sonoran Desert Toad Bufo alvareus has secretions that can cause hallucinations. (Cane toad photo: K. Kriger)
Toxins
Most toxic amphibians (like cane toads or poison dart frogs) accumulate their toxins from the insects they eat. But Australia's critically endangered Corroboree frogs Pseudophryne corroboree and P. pengilleyi manufacture their own toxins. They may be the only vertebrates capable of such a feat. (Photo credit unknown)
What's a herpetologist?
A herpetologist is a person who studies amphibians and/or reptiles. A batrachologist is a more specific term, used to denote one who studies amphibians, though this term is only rarely used.
What's up with the 6-legged frogs?
Frog deformities have caused alarm since the early 1990's, when high numbers of frogs in the Midwest were found with missing limbs, extra limbs or other developmental abnormalities. Many of these deformations are caused by a trematode parasite Ribeiroia ondatrae that burrows into tadpoles' hind limbs. Why did the malformation rate increase so dramatically in the last two decades? This is unknown, but it may be due to increased levels of eutrophication (an un-natural state caused by excessive amounts of fertilizer entering a water body), which allowed snails that are used by the trematode as an intermediary host to increase in numbers, thus providing optimal breeding conditions for the trematode. Furthermore, pesticides have been shown to weaken frogs' immune systems and make them more vulnerable to trematode infections. The photo on the right is a 6-legged Spotted Grass Frog Limnodynastes tasmaniensis. Kind of cool, but in a not-so-cool kind of way. (Photo credits unknown).
Old tadpoles
Some frogs breed in ephemeral pools that form after heavy rains. To ensure that their tadpoles do not die when their puddle dries, the tadpoles are often adapted to metamorphose quickly, perhaps within a week or two. Other frogs, however, like the Tailed frog Ascaphus truei from the Pacific Northwest or Australia's Barred Frog Mixophyes live in permanent ponds or streams and can remain in the tadpole stage for 2 or 3 years. (Photo: M. fasciolatus by K. Kriger)
Nice eyes
Speaking of Barred Frogs, the eyes of Fleay's Barred Frog Mixophyes fleayi actually change color as they get older. Juveniles have partially red eyes, but in adults, the red has changed to blue. (Photos: K. Kriger)
Frozen frogs
Wood frogs Rana sylvatica are the only North American frog that lives above the Arctic Circle. Frogs are ectotherms (cold-blooded) meaning they cannot internally control their body temperatures. Wood frogs are adapted to cold winters being able to survive a deep freeze: Their breathing, blood flow, and heartbeat stop, and ice crystals form beneath their skin. While ice crystals in human skin would result in serious problems (frostbite), wood frogs are safe because high glycogen levels in their cells act like anti-freeze, restricting the frozen areas to the extra-cellular fluid, where no tissue damage will occur. Cool frogs!
How long do frogs live?
Some species only live a few years, but many live 6 or 7 years. The African Clawed Frog Xenopus laevis and the Green Tree Frog Litoria caerulea can live about 30 years in captivity. Determining their life span in the wild is difficult, but if anybody wants to follow some frogs around for a couple decades, please let us know. (Photo: L. caerulea by K. Kriger)
Burrowing frogs
Frogs inhabit some of the driest regions on Earth. As frogs need to remain moist to survive, some frogs burrow underground to avoid the hot dry weather up above. They have specialized shovel-like pads on their arms or legs that let them to go up to 1.5 m (5 ft) down. If no rains come, that's fine. These frogs slow down their metabolism and enter a state called aestivation, which is similar to hibernation. And they shed layers of skin that surround them like a protective cocoon to retain moisture. Some frogs remain underground for 10 months. When the rains come, these frogs appear en masse on the surface for the biggest party of the year. (Photo: Ornate Burrowing frog Limnodynastes ornatus in New South Wales, by K. Kriger)
Check out this excellent video about burrowing frogs in Africa:
Future cure for AIDS?
Skin secretions from at least three species of Australian frogs (the Green Treefrog Litoria caerulea, the Southern Orange-eyed Treefrog Litoria chloris, and the Green-Eyed Treefrog Litoria genimaculata) can completely inhibit HIV, the virus that causes AIDS. (Photo of L. chloris by K. Kriger)
Frogs like to party
OK, so now that we know Southern Orange-eyed Treefrogs probably aren't going to get AIDS, this seems like the appropriate time to show the following video. This one's for the people who've gotten this far down the web page but still aren't sure if they think frogs are cool or not. Make sure your speakers are on...
Please embed this video on your web page if you like it. Note that frogs only party when the temperature and recent rainfall are just right. Climate change therefore would act a bit like the cops did when you were in high school and held that party at your parents' place. (Video by K. Kriger)
Do any amphibians have internal fertilization?
Most frogs and toads have external fertilization (eggs are laid outside of the female's body and then fertilized by the male), but the Tailed Frog Ascaphus truei, which lives in the US Pacific Northwest, has internal fertilization. Many salamanders have internal fertilization as well. Males drop a spermatophore (a gelatinous mass of sperm, more or less) in their favorite location. The lucky female then comes along and pick up this spermatophore with her cloaca to fertilize the eggs inside her body. Caecilians are the only group of amphibians in which all species utilize internal fertilization.
Why do frogs have two names?
Frogs have both a common name and a scientific name, which is in Latin. Thus the African Clawed Frog is also known as Xenopus laevis. The scientific name consists of a frog's genus followed by its species (this is called binomial nomenclature). Carl Linnaeus devised this system in the 18th century so that scientists could be certain they were always referring to the correct species. For instance, there is a 'Green Treefrog' in Europe, America and Australia, but they are all different species: Hyla arborea, Hyla cinerea and Litoria caerulea.
Do frogs have eyelids?
They do, and they also have a clear nictitating membrane, which allows them to protect their eyes without obstructing their vision. You can see the nictitating membrane on this partially submerged Gray Treefrog Hyla versicolor (Photo: K. Kriger)
Long Jump
Australia's Striped Rocket Frog Litoria nasuta can jump a distance equivalent to 55 times its body length! That would be like you jumping a football field! How do they do that? Their legs are twice as long as the rest of their body, and their leg muscles are 1/3 of their overall weight. These frogs are so cool we had to put a picture of one on our Frogs of Australia poster! (Photo taken at the Booyal Crossing, west of Bundaberg, Queensland: K. Kriger)
This page is continually being updated with more Cool Frog Facts, so check back soon!
Please feel free to submit a cool frog fact, or send us a photo relevant to one of the facts listed above, if we do not already have a photo.
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Poison Dart Frogs