Frogs, constituting the order Anura, represent the most diverse and successful group within the class Amphibia, encompassing over 7,600 to nearly 7,800 recognized species worldwide (Animalfact.com; BBC Earth, 2024; TRVST, 2024). The term “amphibian,” signifying “two lives,” accurately reflects their unique lifecycle, which typically progresses from aquatic larval stages to terrestrial or semi-aquatic adult forms (Countryfile.com, 2020; Sussex Wildlife Trust, 2022). While often used interchangeably, “toads” are scientifically classified as a type of frog, generally characterized by drier, wartier skin, shorter hind limbs, and a preference for drier habitats compared to the smooth, moist-skinned, long-legged “true frogs” (Burke Museum; Countryfile.com, 2020; RSPCA; Sussex Wildlife Trust, 2022; TRVST, 2024). All anurans are tailless in their adult stage, a characteristic reflected in their order name derived from Greek for “without a tail” (TRVST, 2024; Zug, 2025).
Anatomy and Physiology
Adult frogs possess distinct anatomical features adapted for their dual existence. They typically exhibit protruding eyes, strong webbed hind feet for leaping and swimming, and lack tails (Britannica; The Wildlife Trusts). Their skin is smooth, moist, and glandular, playing a crucial role in respiration (cutaneous respiration), particularly when submerged or resting (Animalfact.com; BBC Earth, 2024; RSPCA). Frogs also breathe through sac-like lungs and the moist lining of their mouths (Animalfact.com). Uniquely, they do not drink water in the conventional sense but absorb it directly through a specialized “drinking patch” on their belly and thighs (BBC Earth, 2024; Burke Museum). Their hearing apparatus, the tympanum (eardrum), is visible behind the eye and is remarkably linked to their lungs, enabling them to equalize pressure and locate sounds without damaging their hearing from their own loud calls (Burke Museum). Frogs typically swallow their prey whole, utilizing their eyeballs to push food down their throats (Burke Museum). Most frogs possess weak maxillary teeth along their upper jaw; their tongue, attached at the front of the lower jaw, is rapidly extended to catch prey. However, some species, such as the African clawed frog, lack a tongue entirely (Animalfact.com).
The skeletal structure of frogs is highly specialized for jumping, featuring fused bones in the limbs (e.g., tibia, fibula, tarsals in the hindlimb; radius and ulna in the forelimb), elongated metatarsals, and an extended ilium forming a flexible joint with the sacrum. In adults, the tail vertebrae are fused into a rod-like urostyle, which remains retracted within the pelvis, providing stability during leaps (Animalfact.com).
During colder months, some frog species, such as wood frogs (Rana sylvatica), have evolved a remarkable ability to tolerate freezing. They prepare for winter by storing glycogen in their liver, which is rapidly converted into glucose when temperatures drop below freezing. This glucose acts as an antifreeze, with blood glucose levels increasing up to 200-fold. These freeze-tolerant frogs can evacuate water from major organs, allowing up to 65% of their body water in intercellular spaces to freeze without damage, while glucose protects the remaining intracellular water. Though they appear lifeless when frozen, a mid-winter thaw can prompt their recovery, with metabolism resuming as the organs with the highest glucose levels thaw first (McLane, 2002). Amphibians that hibernate underwater in mud can continue to absorb oxygen through their skin (Burke Museum; Canal & River Trust).
Diet and Life Cycle
The diet of a frog undergoes a significant transformation throughout its life. Tadpoles, the larval stage, are typically herbivorous, feeding on algae and aquatic plant matter (Animalfact.com; Britannica; National Geographic Kids; Sussex Wildlife Trust, 2022; Wildlife Aid Foundation). As they mature through metamorphosis, adult frogs become primarily carnivorous insectivores, consuming a wide array of insects such as flies, mosquitoes, beetles, spiders, slugs, and worms (Animalfact.com; BBC Earth, 2024; Britannica; Wildlife Aid Foundation). They use their long, sticky tongues to snatch fast-moving prey (Animalfact.com; Britannica). Larger species, such as the Goliath frog (which can reach 32 cm and 3.25 kg) and the African bullfrog, are known to consume larger prey, including small mammals, birds, other frogs, rodents, and reptiles (Animalfact.com; BBC Earth, 2024; Britannica).
The frog life cycle involves an astonishing transformation called metamorphosis (National Geographic Kids). It begins in early spring with adults emerging from hibernation in locations like pond mud, under rocks, or in compost heaps (Froglife; The Wildlife Trusts; Wildlife Aid Foundation). They migrate to ponds to breed, laying jelly-like eggs, known as “spawn,” which can be found in clumps (frogs) or strings (toads) (Countryfile.com, 2020; Froglife; National Geographic Kids; RSPCA; Sussex Wildlife Trust, 2022). A female common frog may lay up to 4,000 eggs in a single season (Sussex Wildlife Trust, 2022; Wildlife Aid Foundation). Most species spawn early in the season, allowing their young sufficient time to grow and metamorphose before winter (Countryfile.com, 2020). Tadpoles hatch with gills, a mouth, and a tail, initially absorbing nutrients from their yolk. Over approximately 14 weeks, they develop back and then front legs, their body shape changes, and they begin to eat insects. Their tails then shrink, and skin grows over their gills as lungs and eardrums develop, preparing them for terrestrial life. Tadpoles can even control the timing of their metamorphosis, accelerating it in dangerous environments or delaying it if conditions on land are unfavorable (National Geographic Kids).
Reproduction and Behavior
Mating rituals among frogs are diverse, involving sophisticated croaks, fighting, and sometimes even playing dead (BBC Earth, 2024). In environments with high ambient noise, such as near waterfalls, some species have evolved unique communication strategies. The Ecuadorian glass frog (Sachatamia orejuela), for instance, employs both high-frequency croaking and visual displays, including rapid hand-waving, feet-flashing, and head-bobbing, to attract mates. This adaptation, observed in various unrelated species, is an example of convergent evolution (Dvorsky, 2021). The Bombay night frog (Nyctibatrachus humayuni) exhibits a particularly unusual mating position, termed “dorsal straddle,” where the male steadies itself on nearby vegetation and releases semen onto the female’s back without grasping her, a method previously unobserved in frogs. This contrasts with the six other known frog mating positions, where the male typically clasps the female’s waist, armpits, head, or uses a gluey substance, or mates back-to-back or on her head (Sample, 2016).
Diversity, Distribution, and Conservation
Frogs inhabit diverse environments globally, from tropical rainforests to subarctic regions, including deserts and mountains (Animalfact.com; TRVST, 2024). Species vary dramatically in size, from the minuscule Paedophryne amauensis (7.7 mm) to the giant Goliath frog (up to 35 cm or 14 inches long and 3.25 kg) (Animalfact.com; BBC Earth, 2024; TRVST, 2024).
Many frogs utilize camouflage, displaying subtle, earthy colors to blend into their surroundings. Examples include the Vietnamese mossy frog, which resembles lichen; the pebble toad, which blends with sandstone; and the long-nosed horned frog, which mimics a crispy leaf. The glass frog even achieves transparency in its belly and chest to become nearly invisible against foliage (BBC Earth, 2024). Conversely, many frog species are poisonous, often displaying bright, aposematic coloration to warn predators of their toxicity. The golden poison frog, for example, is one of the most toxic animals on Earth, with its venom historically used by indigenous communities for hunting. Its toxicity is believed to derive from its specialized diet of ants and termites (Animalfact.com; BBC Earth, 2024; National Geographic; TRVST, 2024). Some frogs, like the South American polka dot tree frog, can even be fluorescent and glow under ultraviolet light, potentially aiding communication (BBC Earth, 2024).
In the UK, native species include the common frog, common toad, natterjack toad (which is rare), and the reintroduced northern pool frog (Amphibian and Reptile Conservation; Countryfile.com, 2020; RSPCA; Sussex Wildlife Trust, 2022; Canal & River Trust). British Columbia, Canada, hosts a range of species, including the Boreal chorus frog, Columbia spotted frog, and endangered species like the Northern leopard frog and Oregon spotted frog (Province of British Columbia, 2019).
Despite their adaptability, many frog populations face significant threats, including habitat destruction (e.g., reduction of ponds and wetlands due to urbanization and agriculture), warming temperatures, pollution (e.g., pesticides, chemical runoff), and devastating skin fungi, particularly chytridiomycosis (ABC Net Au, 2008; BBC Earth, 2024; Froglife; Wildlife Aid Foundation). These threats have led to significant declines, with 8 Australian species already extinct and 47 more threatened, and the critical status of species like the Corroboree frog (ABC Net Au, 2008; TRVST, 2024). Conservation efforts are crucial, with organizations like Froglife and the Amphibian and Reptile Conservation Trust working to protect these species and their habitats (Amphibian and Reptile Conservation; Froglife). Initiatives include building garden ponds, avoiding chemicals, providing shelter, and participating in local amphibian groups. Zoos and schools are also engaging in breeding programs to help threatened species (ABC Net Au, 2008; Reddit; Wildlife Aid Foundation).
Cultural Significance
Frogs also feature prominently in human culture. Rayne, Louisiana, proudly declares itself the “frog capital of the world,” celebrating its historical role in exporting frogs as a delicacy to France and its unique annual frog festival (McNamara, 2025). The town also boasts a connection to early space exploration, as two bullfrogs from Rayne were sent into orbit by NASA in 1970 to study the effects of weightlessness on their ears, which are similar to human ears (McNamara, 2025). It is important to note, however, that while the Texas Christian University (TCU) athletic teams are known as the “Horned Frogs,” their official mascot, SuperFrog, is a costumed depiction of the Texas horned lizard (Phrynosoma cornutum), a reptile, not an amphibian. This symbol was adopted by the university in 1897 (Grokipedia). This distinction underscores the varied and sometimes ambiguous ways the term “frog” is used in popular culture.
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