

Temporal range:
Early JurassicPresent, 200–0 Ma
Various types of frogs.
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Amphibia
Clade: Salientia
Order: Anura
Duméril, 1806 (as Anoures)

List of Anuran families

Native distribution of frogs (in green)
Variegated golden frog (Mantella baroni) in the Ranomafana National Park of Madagascar

An adult frog has a stout body, protruding eyes, anteriorly-attached tongue, limbs folded underneath, and no tail (except in tailed frogs). Frogs have glandular skin, with secretions ranging from distasteful to toxic. Their skin varies in colour from well-camouflaged dappled brown, grey and green to vivid patterns of bright red or yellow and black to show toxicity and ward off predators. Adult frogs live in fresh water and on dry land; some species are adapted for living underground or in trees.

Frogs typically lay their eggs in water. The eggs hatch into aquatic larvae called tadpoles that have tails and internal gills. They have highly specialized rasping mouth parts suitable for herbivorous, omnivorous or planktivorous diets. The life cycle is completed when they metamorphose into adults. A few species deposit eggs on land or bypass the tadpole stage. Adult frogs generally have a carnivorous diet consisting of small invertebrates, but omnivorous species exist and a few feed on plant matter. Frog skin has a rich microbiome which is important to their health. Frogs are extremely efficient at converting what they eat into body mass. They are an important food source for predators and part of the food web dynamics of many of the world's ecosystems. The skin is semi-permeable, making them susceptible to dehydration, so they either live in moist places or have special adaptations to deal with dry habitats. Frogs produce a wide range of vocalizations, particularly in their breeding season, and exhibit many different kinds of complex behaviors to attract mates, to fend off predators and to generally survive.

Frogs are valued as food by humans and also have many cultural roles in literature, symbolism and religion. They are also seen as environmental bellwethers, with declines in frog populations often viewed as early warning signs of environmental damage. Frog populations have declined significantly since the 1950s. More than one third of species are considered to be threatened with extinction and over 120 are believed to have become extinct since the 1980s. The number of malformations among frogs is on the rise and an emerging fungal disease, chytridiomycosis, has spread around the world. Conservation biologists are working to understand the causes of these problems and to resolve them.

Etymology and taxonomy

The use of the common names "frog" and "toad" has no taxonomic justification. From a classification perspective, all members of the order Anura are frogs, but only members of the family Bufonidae are considered "true toads". The use of the term "frog" in common names usually refers to species that are aquatic or semi-aquatic and have smooth, moist skins; the term "toad" generally refers to species that are terrestrial with dry, warty skins.[2][3] There are numerous exceptions to this rule. The European fire-bellied toad (Bombina bombina) has a slightly warty skin and prefers a watery habitat[4] whereas the Panamanian golden frog (Atelopus zeteki) is in the toad family Bufonidae and has a smooth skin.[5]


The origin of the order name Anura—and its original spelling Anoures—is the Ancient Greek "alpha privative" prefix ἀν- (an-) "without", and οὐρά (ourá), meaning "animal tail". It refers to the tailless character of these amphibians.[6][7][8]

The origins of the word frog are uncertain and debated.[9] The word is first attested in Old English as frogga, but the usual Old English word for the frog was frosc (with variants such as frox and forsc), and it is agreed that the word frog is somehow related to this. Old English frosc remained in dialectal use in English as frosh and frosk into the nineteenth century,[10] and is paralleled widely in other Germanic languages, with examples in the modern languages including German Frosch, Icelandic froskur, and Dutch (kik)vors.[9] These words allow us to reconstruct a Common Germanic ancestor *froskaz.[11] The third edition of the Oxford English Dictionary finds that the etymology of *froskaz is uncertain, but agrees with arguments that it could plausibly derive from a Proto-Indo-European base along the lines of *preu = "jump".[9][12]

How Old English frosc gave rise to frogga is, however, uncertain, as the development does not involve a regular sound-change. Instead, it seems that there was a trend in Old English to coin nicknames for animals ending in -g, with examples—themselves all of uncertain etymology—including dog, hog, pig, stag, and (ear)wig. Frog appears to have been adapted from frosc as part of this trend.[9]

Meanwhile, the word toad, first attested as Old English tādige, is unique to English and is likewise of uncertain etymology.[13] It is the basis for the word tadpole, first attested as Middle English taddepol, apparently meaning 'toad-head'.[14]


About 88% of amphibian species are classified in the order Anura.[15] These include over 7,100 species in 55 families, of which the Craugastoridae (850 spp.), Hylidae (724 spp.), Microhylidae (688 spp.), and Bufonidae (621 spp.) are the richest in species.[16]

European fire-bellied toad (Bombina bombina)


Panamanian golden frog (Atelopus zeteki).

Frogs and toads are broadly classified into three suborders: Archaeobatrachia, which includes four families of primitive frogs; Mesobatrachia, which includes five families of more evolutionary intermediate frogs; and Neobatrachia, by far the largest group, which contains the remaining families of modern frogs, including most common species throughout the world. The suborder Neobatrachia is further divided into the two superfamilies Hyloidea and Ranoidea.[19] This classification is based on such morphological features as the number of vertebrae, the structure of the pectoral girdle, and the morphology of tadpoles. While this classification is largely accepted, relationships among families of frogs are still debated.[20]

Some species of anurans hybridize readily. For instance, the edible frog (Pelophylax esculentus) is a hybrid between the pool frog (P. lessonae) and the marsh frog (P. ridibundus).[21] The fire-bellied toads Bombina bombina and B. variegata are similar in forming hybrids. These are less fertile than their parents, giving rise to a hybrid zone where the hybrids are prevalent.[22]



A fossilized frog from the Czech Republic, possibly Palaeobatrachus gigas.



The earliest known "true frogs" that fall into the anuran lineage proper all lived in the early Jurassic period.[2][31] One such early frog species, Prosalirus bitis, was discovered in 1995 in the Kayenta Formation of Arizona and dates back to the Early Jurassic epoch (199.6 to 175 million years ago), making Prosalirus somewhat more recent than Triadobatrachus.[32] Like the latter, Prosalirus did not have greatly enlarged legs, but had the typical three-pronged pelvic structure of modern frogs. Unlike Triadobatrachus, Prosalirus had already lost nearly all of its tail[33] and was well adapted for jumping.[34] Another Early Jurassic frog is Vieraella herbsti, which is known only from dorsal and ventral impressions of a single animal and was estimated to be 33 mm (1.3 in) from snout to vent. Notobatrachus degiustoi from the middle Jurassic is slightly younger, about 155–170 million years old. The main evolutionary changes in this species involved the shortening of the body and the loss of the tail. The evolution of modern Anura likely was complete by the Jurassic period. Since then, evolutionary changes in chromosome numbers have taken place about 20 times faster in mammals than in frogs, which means speciation is occurring more rapidly in mammals.[35]

According to genetic studies, the families Hyloidea, Microhylidae, and the clade Natatanura (comprising about 88% of living frogs) diversified simultaneously some 66 million years ago, soon after the Cretaceous–Paleogene extinction event associated with the Chicxulub impactor. All origins of arboreality (e.g. in Hyloidea and Natatanura) follow from that time and the resurgence of forest that occurred afterwards.[36][37]

Frog fossils have been found on all of the earth's continents.[38][39] In 2020, it was announced that 40 million year old helmeted frog fossils had been discovered by a team of vertebrate paleontologists in Seymour Island on the Antarctic Peninsula, indicating that this region was once home to frogs related to those now living in South American Nothofagus forest.[40]


A cladogram showing the relationships of the different families of frogs in the clade Anura can be seen in the table below. This diagram, in the form of a tree, shows how each frog family is related to other families, with each node representing a point of common ancestry. It is based on Frost et al. (2006),[41] Heinicke et al. (2009)[42] and Pyron and Wiens (2011).[43]













































































Morphology and physiology


Frogs have no tail, except as larvae, and most have long hind legs, elongated ankle bones, webbed toes, no claws, large eyes, and a smooth or warty skin. They have short vertebral columns, with no more than 10 free vertebrae and fused tailbones (urostyle or coccyx).[44] Like other amphibians, oxygen can pass through their highly permeable skins. This unique feature allows them to remain in places without access to the air, respiring through their skins.[45] Ribs are generally absent, so the lungs are filled by buccal pumping and a frog deprived of its lungs can maintain its body functions without them.[45] For the skin to serve as a respiratory organ, it must remain moist. This makes frogs susceptible to various substances they may encounter in the environment, some of which may be toxic and can dissolve in the water film and be passed into their bloodstream. This may be one of the causes of the worldwide decline in frog populations.[46][47][48][49]

Frogs range in size from Paedophryne amauensis of Papua New Guinea that is 7.7 mm (0.30 in) in snout–to–vent length[50] to the up to 32 cm (13 in) and 3.25 kg (7.2 lb) goliath frog (Conraua goliath) of central Africa.[51] There are prehistoric, extinct species that reached even larger sizes.[52] The skin hangs loosely on the body because of the lack of loose connective tissue. Frogs have three eyelid membranes: one is transparent to protect the eyes underwater, and two vary from translucent to opaque. They have a tympanum on each side of their heads which is involved in hearing and, in some species, is covered by skin. True toads completely lack teeth, but most frogs have them, specifically pedicellate teeth in which the crown is separated from the root by fibrous tissue. These are on the edge of the upper jaw and vomerine teeth are also on the roof of their mouths. No teeth are in the lower jaw and frogs usually swallow their food whole. The teeth are mainly used to grip the prey and keep it in place until swallowed, a process assisted by retracting the eyes into the head.[53] The African bullfrog (Pyxicephalus), which preys on relatively large animals such as mice and other frogs, has cone shaped bony projections called odontoid processes at the front of the lower jaw which function like teeth.[15]


Feet and legs


Webbed hind foot of common frog
(Rana temporaria)


Many frogs have webbed feet and the degree of webbing is directly proportional to the amount of time the species spends in the water.[55] The completely aquatic African dwarf frog (Hymenochirus sp.) has fully webbed toes, whereas those of White's tree frog (Litoria caerulea), an arboreal species, are only a quarter or half webbed.[56] Exceptions include flying frogs in the Hylidae and Rhacophoridae, which also have fully webbed toes used in gliding.




Sometimes during the tadpole stage, one of the developing rear legs is eaten by a predator such as a dragonfly nymph. In some cases, the full leg still grows, but in others it does not, although the frog may still live out its normal lifespan with only three limbs. Occasionally, a parasitic flatworm (Ribeiroia ondatrae) digs into the rear of a tadpole, causing a rearrangement of the limb bud cells and the frog develops one or more extra legs.[60]



A frog's skin is protective, has a respiratory function, can absorb water, and helps control body temperature. It has many glands, particularly on the head and back, which often exude distasteful and toxic substances (granular glands). The secretion is often sticky and helps keep the skin moist, protects against the entry of moulds and bacteria, and make the animal slippery and more able to escape from predators.[61] The skin is shed every few weeks. It usually splits down the middle of the back and across the belly, and the frog pulls its arms and legs free. The sloughed skin is then worked towards the head where it is quickly eaten.[62]



Some species have bony plates embedded in their skin, a trait that appears to have evolved independently several times.[67] In certain other species, the skin at the top of the head is compacted and the connective tissue of the dermis is co-ossified with the bones of the skull (exostosis).[68][69]


Respiration and circulation



Some species of frog have adaptations that allow them to survive in oxygen deficient water. The Titicaca water frog (Telmatobius culeus) is one such species and has wrinkly skin that increases its surface area to enhance gas exchange. It normally makes no use of its rudimentary lungs but will sometimes raise and lower its body rhythmically while on the lake bed to increase the flow of water around it.[75]


Digestion and excretion

Frogs have maxillary teeth along their upper jaw which are used to hold food before it is swallowed. These teeth are very weak, and cannot be used to chew or catch and harm agile prey. Instead, the frog uses its sticky, cleft tongue to catch flies and other small moving prey. The tongue normally lies coiled in the mouth, free at the back and attached to the mandible at the front. It can be shot out and retracted at great speed.[55] Some frogs have no tongue and just stuff food into their mouths with their hands.[55] The eyes assist in the swallowing of food as they can be retracted through holes in the skull and help push food down the throat.[55] The food then moves through the oesophagus into the stomach where digestive enzymes are added and it is churned up. It then proceeds to the small intestine (duodenum and ileum) where most digestion occurs. Pancreatic juice from the pancreas, and bile, produced by the liver and stored in the gallbladder, are secreted into the small intestine, where the fluids digest the food and the nutrients are absorbed. The food residue passes into the large intestine where excess water is removed and the wastes are passed out through the cloaca.[76] The recently discovered Prometheus Frog has been reported to sometimes eat cooked or burnt food from areas affected by forest fires.[77]


Reproductive system


When frogs mate, the male climbs on the back of the female and wraps his fore limbs round her body, either behind the front legs or just in front of the hind legs. This position is called amplexus and may be held for several days.[80] The male frog has certain hormone-dependent secondary sexual characteristics. These include the development of special pads on his thumbs in the breeding season, to give him a firm hold.[81] The grip of the male frog during amplexus stimulates the female to release eggs, usually wrapped in jelly, as spawn.[79] In many species the male is smaller and slimmer than the female. Males have vocal cords and make a range of croaks, particularly in the breeding season, and in some species they also have vocal sacs to amplify the sound.[79]

Nervous system

Frogs have a highly developed nervous system that consists of a brain, spinal cord and nerves. Many parts of frog brains correspond with those of humans. It consists of two olfactory lobes, two cerebral hemispheres, a pineal body, two optic lobes, a cerebellum and a medulla oblongata. Muscular coordination and posture are controlled by the cerebellum, and the medulla oblongata regulates respiration, digestion and other automatic functions.[79] The relative size of the cerebrum in frogs is much smaller than it is in humans. Frogs have ten pairs of cranial nerves which pass information from the outside directly to the brain, and ten pairs of spinal nerves which pass information from the extremities to the brain through the spinal cord.[79] By contrast, all amniotes (mammals, birds and reptiles) have twelve pairs of cranial nerves.[82]




The distant vision of a frog is better than its near vision. Calling frogs will quickly become silent when they see an intruder or even a moving shadow but the closer an object is, the less well it is seen.[84] When a frog shoots out its tongue to catch an insect it is reacting to a small moving object that it cannot see well and must line it up precisely beforehand because it shuts its eyes as the tongue is extended.[55] Although it was formerly debated,[85] more recent research has shown that frogs can see in colour, even in very low light.[86]





A male Dendropsophus microcephalus displaying its vocal sac during its call.
Advertisement call of male Atelopus franciscus

The call or croak of a frog is unique to its species. Frogs create this sound by passing air through the larynx in the throat. In most calling frogs, the sound is amplified by one or more vocal sacs, membranes of skin under the throat or on the corner of the mouth, that distend during the amplification of the call. Some frog calls are so loud that they can be heard up to a mile away.[90] Additionally, some species have been found to use man-made structures such as drain pipes for artificial amplification of their call.[91]



A different call is emitted by a male frog or unreceptive female when mounted by another male. This is a distinct chirruping sound and is accompanied by a vibration of the body.[95] Tree frogs and some non-aquatic species have a rain call that they make on the basis of humidity cues prior to a shower.[95] Many species also have a territorial call that is used to drive away other males. All of these calls are emitted with the mouth of the frog closed.[95] A distress call, emitted by some frogs when they are in danger, is produced with the mouth open resulting in a higher-pitched call. It is typically used when the frog has been grabbed by a predator and may serve to distract or disorientate the attacker so that it releases the frog.[95]

Distinctive low "jug-o-rum" sound of Banded bullfrog.

Many species of frog have deep calls. The croak of the American bullfrog (Rana catesbiana) is sometimes written as "jug o' rum".[96] The Pacific tree frog (Pseudacris regilla) produces the onomatopoeic "ribbit" often heard in films.[97] Other renderings of frog calls into speech include "brekekekex koax koax", the call of the marsh frog (Pelophylax ridibundus) in The Frogs, an Ancient Greek comic drama by Aristophanes.[98] The calls of the Concave-eared torrent frog (Amolops tormotus) are unusual in many aspects. The males are notable for their varieties of calls where upward and downward frequency modulations take place. When they communicate, they produce calls that fall in the ultrasound frequency range. The last aspect that makes this species of frog's calls unusual is that nonlinear acoustic phenomena are important components in their acoustic signals.[99]







Frogs are generally recognized as exceptional jumpers and, relative to their size, the best jumpers of all vertebrates.[104] The striped rocket frog, Litoria nasuta, can leap over 2 metres (6 ft 7 in), a distance that is more than fifty times its body length of 5.5 centimetres (2.2 in).[105] There are tremendous differences between species in jumping capability. Within a species, jump distance increases with increasing size, but relative jumping distance (body-lengths jumped) decreases. The Indian skipper frog (Euphlyctis cyanophlyctis) has the ability to leap out of the water from a position floating on the surface.[106] The tiny northern cricket frog (Acris crepitans) can "skitter" across the surface of a pond with a series of short rapid jumps.[107]


Early hatching of froglets can have negative effects on frog jumping performance and overall locomotion.[110] The hindlimbs are unable to completely form, which results in them being shorter and much weaker relative to a normal hatching froglet.[110] Early hatching froglets may tend to depend on other forms of locomotion more often, such as swimming and walking.[110]

Walking and running
Phrynomantis bifasciatus walking on a level surface


The red-legged running frog (Kassina maculata) has short, slim hind limbs unsuited to jumping. It can move fast by using a running gait in which the two hind legs are used alternately. Slow-motion photography shows, unlike a horse that can trot or gallop, the frog's gait remained similar at slow, medium, and fast speeds.[114] This species can also climb trees and shrubs, and does so at night to catch insects.[115] The Indian skipper frog (Euphlyctis cyanophlyctis) has broad feet and can run across the surface of the water for several metres (yards).[107]

Common toad (Bufo bufo) swimming.




Purple frog (Nasikabatrachus sahyadrensis).



Group of Glass frogs



During the evolutionary history of frogs, several different groups have independently taken to the air.[127] Some frogs in the tropical rainforest are specially adapted for gliding from tree to tree or parachuting to the forest floor. Typical of them is Wallace's flying frog (Rhacophorus nigropalmatus) from Malaysia and Borneo. It has large feet with the fingertips expanded into flat adhesive discs and the digits fully webbed. Flaps of skin occur on the lateral margins of the limbs and across the tail region. With the digits splayed, the limbs outstretched, and these flaps spread, it can glide considerable distances, but is unable to undertake powered flight.[128] It can alter its direction of travel and navigate distances of up to 15 m (49 ft) between trees.[129]

Life history

Life cycle of the green frog
(Rana clamitans).





Male and female common toads (Bufo bufo) in amplexus.



Life cycle

Eggs / frogspawn



The shape and size of the egg mass is characteristic of the species. Ranids tend to produce globular clusters containing large numbers of eggs whereas bufonids produce long, cylindrical strings. The tiny yellow-striped pygmy eleuth (Eleutherodactylus limbatus) lays eggs singly, burying them in moist soil.[138] The smoky jungle frog (Leptodactylus pentadactylus) makes a nest of foam in a hollow. The eggs hatch when the nest is flooded, or the tadpoles may complete their development in the foam if flooding does not occur.[139] The red-eyed treefrog (Agalychnis callidryas) deposits its eggs on a leaf above a pool and when they hatch, the larvae fall into the water below.[140] The larvae developing in the eggs can detect vibrations caused by nearby predatory wasps or snakes, and will hatch early to avoid being eaten.[141] In general, the length of the egg stage depends on the species and the environmental conditions. Aquatic eggs normally hatch within one week when the capsule splits as a result of enzymes released by the developing larvae.[142]


Frogspawn development.






At the end of the tadpole stage, a frog undergoes metamorphosis in which its body makes a sudden transition into the adult form. This metamorphosis typically lasts only 24 hours, and is initiated by production of the hormone thyroxine. This causes different tissues to develop in different ways. The principal changes that take place include the development of the lungs and the disappearance of the gills and gill pouch, making the front legs visible. The lower jaw transforms into the big mandible of the carnivorous adult, and the long, spiral gut of the herbivorous tadpole is replaced by the typical short gut of a predator.[142] The nervous system becomes adapted for hearing and stereoscopic vision, and for new methods of locomotion and feeding.[142] The eyes are repositioned higher up on the head and the eyelids and associated glands are formed. The eardrum, middle ear, and inner ear are developed. The skin becomes thicker and tougher, the lateral line system is lost, and skin glands are developed.[142] The final stage is the disappearance of the tail, but this takes place rather later, the tissue being used to produce a spurt of growth in the limbs.[148] Frogs are at their most vulnerable to predators when they are undergoing metamorphosis. At this time, the tail is being lost and locomotion by means of limbs is only just becoming established.[111]


A Xenopus laevis froglet after metamorphosis.

After metamorphosis, young adults may disperse into terrestrial habitats or continue to live in water. Almost all frog species are carnivorous as adults, preying on invertebrates, including arthropods, worms, snails, and slugs. A few of the larger ones may eat other frogs, small mammals, and fish. Some frogs use their sticky tongues to catch fast-moving prey, while others push food into their mouths with their hands. A few species also eat plant matter; the tree frog Xenohyla truncata is partly herbivorous, its diet including a large proportion of fruit,[149] Leptodactylus mystaceus has been found to eat plants,[150][151] and folivory occurs in Euphlyctis hexadactylus, with plants constituting 79.5% of its diet by volume.[152] Adult frogs are themselves attacked by many predators. The northern leopard frog (Rana pipiens) is eaten by herons, hawks, fish, large salamanders, snakes, raccoons, skunks, mink, bullfrogs, and other animals.[153]

A trophic pyramid showing frogs as primary predators.



Parental care

Male common midwife toad with eggs
(Alytes obstetricans).
Pouched frog (Assa darlingtoni)

Although care of offspring is poorly understood in frogs, up to an estimated 20% of amphibian species may care for their young in some way.[158] The evolution of parental care in frogs is driven primarily by the size of the water body in which they breed. Those that breed in smaller water bodies tend to have greater and more complex parental care behaviour.[159] Because predation of eggs and larvae is high in large water bodies, some frog species started to lay their eggs on land. Once this happened, the desiccating terrestrial environment demands that one or both parents keep them moist to ensure their survival.[160] The subsequent need to transport hatched tadpoles to a water body required an even more intense form of parental care.[159]





The mildly toxic Ranitomeya imitator.
Strawberry poison-dart frog contains numerous alkaloids which deter predators.



A common toad adopting a defensive stance.

Some frogs, such as the poison dart frogs, are especially toxic. The native peoples of South America extract poison from these frogs to apply to their weapons for hunting,[173] although few species are toxic enough to be used for this purpose. At least two non-poisonous frog species in tropical America (Eleutherodactylus gaigei and Lithodytes lineatus) mimic the colouration of dart poison frogs for self-protection.[174][175] Some frogs obtain poisons from the ants and other arthropods they eat.[176] Others, such as the Australian corroboree frogs (Pseudophryne corroboree and Pseudophryne pengilleyi), can synthesize the alkaloids themselves.[177] The chemicals involved may be irritants, hallucinogens, convulsants, nerve poisons or vasoconstrictors. Many predators of frogs have become adapted to tolerate high levels of these poisons, but other creatures, including humans who handle the frogs, may be severely affected.[178]



Although frogs are most diverse in warm regions, a few species like the wood frog even live at the Arctic Circle

Frogs live on all the continents except Antarctica, but they are not present on certain islands, especially those far away from continental land masses.[181][182] Many species are isolated in restricted ranges by changes of climate or inhospitable territory, such as stretches of sea, mountain ridges, deserts, forest clearance, road construction, or other man-made barriers.[183] Usually, a greater diversity of frogs occurs in tropical areas than in temperate regions, such as Europe.[184] Some frogs inhabit arid areas, such as deserts, and rely on specific adaptations to survive. Members of the Australian genus Cyclorana bury themselves underground where they create a water-impervious cocoon in which to aestivate during dry periods. Once it rains, they emerge, find a temporary pool, and breed. Egg and tadpole development is very fast in comparison to those of most other frogs, so breeding can be completed before the pond dries up.[185] Some frog species are adapted to a cold environment. The wood frog (Rana sylvatica), whose habitat extends into the Arctic Circle, buries itself in the ground during winter. Although much of its body freezes during this time, it maintains a high concentration of glucose in its vital organs, which protects them from damage.[55]


Golden toad (Bufo periglenes) – last seen in 1989.

In 2006, of 4,035 species of amphibians that depend on water during some lifecycle stage, 1,356 (33.6%) were considered to be threatened. This is likely to be an underestimate because it excludes 1,427 species for which evidence was insufficient to assess their status.[186] Frog populations have declined dramatically since the 1950s. More than one-third of frog species are considered to be threatened with extinction, and more than 120 species are believed to have become extinct since the 1980s.[187] Among these species are the gastric-brooding frogs of Australia and the golden toad of Costa Rica. The latter is of particular concern to scientists because it inhabited the pristine Monteverde Cloud Forest Reserve and its population crashed in 1987, along with about 20 other frog species in the area. This could not be linked directly to human activities, such as deforestation, and was outside the range of normal fluctuations in population size.[188] Elsewhere, habitat loss is a significant cause of frog population decline, as are pollutants, climate change, increased UVB radiation, and the introduction of non-native predators and competitors.[189] A Canadian study conducted in 2006 suggested heavy traffic in their environment was a larger threat to frog populations than was habitat loss.[190] Emerging infectious diseases, including chytridiomycosis and ranavirus, are also devastating populations.[191][192]

Many environmental scientists believe amphibians, including frogs, are good biological indicators of broader ecosystem health because of their intermediate positions in food chains, their permeable skins, and typically biphasic lives (aquatic larvae and terrestrial adults).[193] It appears that species with both aquatic eggs and larvae are most affected by the decline, while those with direct development are the most resistant.[194]

Deformed mink frog with an extra left leg


In a few cases, captive breeding programs have been established and have largely been successful.[197][198] The World Association of Zoos and Aquariums named 2008 as the "Year of the Frog" in order to draw attention to the conservation issues faced by them.[199]




French cuisses de grenouille.


Originally, they were supplied from local wild populations, but overexploitation led to a diminution in the supply. This resulted in the development of frog farming and a global trade in frogs.[203] The main importing countries are France, Belgium, Luxembourg, and the United States, while the chief exporting nations are Indonesia and China.[203] The annual global trade in the American bullfrog (Rana catesbeiana), mostly farmed in China, varies between 1200 and 2400 tonnes.[204]

The mountain chicken frog, so-called as it tastes of chicken, is now endangered, in part due to human consumption, and was a major food choice of the Dominicans.[205]


Scientific research


Frogs have served as experimental animals throughout the history of science. Eighteenth-century biologist Luigi Galvani discovered the link between electricity and the nervous system by studying frogs.[208] In 1852, H. F. Stannius used a frog's heart in a procedure called a Stannius ligature to demonstrate the ventricle and atria beat independently of each other and at different rates.[209] The African clawed frog or platanna (Xenopus laevis) was first widely used in laboratories in pregnancy tests in the first half of the 20th century. A sample of urine from a pregnant woman injected into a female frog induces it to lay eggs, a discovery made by English zoologist Lancelot Hogben. This is because a hormone, human chorionic gonadotropin, is present in substantial quantities in the urine of women during pregnancy.[210] In 1952, Robert Briggs and Thomas J. King cloned a frog by somatic cell nuclear transfer. This same technique was later used to create Dolly the sheep, and their experiment was the first time a successful nuclear transplantation had been accomplished in higher animals.[211]

Frogs are used in cloning research and other branches of embryology. Although alternative pregnancy tests have been developed, biologists continue to use Xenopus as a model organism in developmental biology because their embryos are large and easy to manipulate, they are readily obtainable, and can easily be kept in the laboratory.[212] Xenopus laevis is increasingly being displaced by its smaller relative, Xenopus tropicalis, which reaches its reproductive age in five months rather than the one to two years for X. laevis,[213] thus facilitating faster studies across generations.

Genomes of Xenopus laevis, X. tropicalis, Rana catesbeiana, Rhinella marina, and Nanorana parkeri have been sequenced and deposited in the NCBI Genome database.[214]

As pets

Due to being inexpensive and relatively easy to care for, many species of frog and toad have become popular as exotic pets, they are undemanding and require low maintenance.


Because frog toxins are extraordinarily diverse, they have raised the interest of biochemists as a "natural pharmacy". The alkaloid epibatidine, a painkiller 200 times more potent than morphine, is made by some species of poison dart frogs. Other chemicals isolated from the skins of frogs may offer resistance to HIV infection.[215] Dart poisons are under active investigation for their potential as therapeutic drugs.[216]


Golden poison frog (Phyllobates terribilis).


Cultural beliefs

Moche frog sculpture



See also


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Further reading

External links