Green Frog, master of the mountain stream

Common Name: Green Frog, Bronze Frog – The provenance of the Germanic word frog is the Sanskrit pravate, meaning ‘he jumps up.’ The bright facial markings and overall greenish-brown hues distinguish the species. The bronze frog is a subspecies in southern North America with darker coloration.

Scientific Name: Rana clamitans – The generic name Rana is the Latin word for frog. The Latin word clamito means ‘to cry loudly or often shout violently.’ The species is noted for its loud and distinctive mating call that sounds like a combination of a plucked banjo string and a jew’s-harp. The species is also known by the name Lithobates clamitans, although this newer nomenclature is controversial. It derives from the Greek words litho meaning ‘stone’ and bates meaning ‘that which walks.’

In that many hiking trails follow the riparian watershed of brooks, streams and ponds, an encounter with a Green Frog is inevitable, as it is the linchpin of the faunal populations that inhabit these areas. While elusive as a matter of self-preservation, the iconic forest denizen may be seldom seen but it is frequently heard in the belly flop splash as it seeks the protection of the aquatic Palladium. In the late summer months during the alpenglow of the waning light, the stentorian banjo-string twang vocalizations of the males in search of a mate reverberate through the woods.

Frogs in general and the Green Frog in particular are highly successful in the habitat that they have chosen to populate, so much so that they have persisted with little change to basic body structure and physiology since the late Permian Period about 300 million years ago, about 50 million years in advance of the dinosaur-dominated Triassic Period. It stands to reason that the amphibians, those vertebrates that are both aquatic and terrestrial, bridged the gap between the oceanic provenance of life (both plant and animal) and its extension to land. The frog-headed, salamander body of the fossil Gerobatrachus discovered in Permian strata in 2008 was dubbed the “frogamander” as the common ancestor to both major orders of the Class Amphibia: The frogs and toads of the Order Anura and the salamanders and newts of the Order Caudata. The ‘true frogs’ of the Family Ranidae are generally distinguished from the ‘true toads’ of the Family Bufonidae in having smooth, moist skin and a mostly aquatic lifestyle. Toads are have dry warty skin and are mostly terrestrial. The success of the ranids is measured in both geographic distribution and in number; they are found on every continent except Antarctica with 55 different genera and about 800 species (numbers vary according to source). There are 250 species in North America. As a large green-bodied frog, the Green Frog is easy to distinguish from other, more colorful frogs. The only exception is the bullfrog, which approximates its coloration and physiognomy. However, the bull frog habituates larger bodies of water such as large ponds and lakes. A more distinguishing feature is their lack of dorsal ridges, which are prominent in the Green Frog.
Bullfrog in a larger pond. Note the smooth dorsal surface

The Green Frog employs crypsis, blending into the greens and browns of streambed ecology both as a means of escaping predation and as a means of stalking prey. Even the green stripe across the lower jaw emulates a blade of grass along the stream bank. In addition to coloration, all frogs have poison glands in their skin consisting of complex nitrogenous compounds. These can vary in efficacy from a mild irritant to a deadly neurotoxin, depending on the species. For most frogs, the Green Frog included, the toxins do not serve to deter predators due to deleterious effect of consumption. Green Frogs are subject to predation that varies according to the stage of their life: frog eggs are consumed by turtles; tadpoles are consumed by a wide variety of aquatic carnivores including the larvae of diving beetles, adult water bugs and the nymph stage of dragonflies; adults are eaten by a variety of birds including crows, herons and ducks and by water and garter snakes. Small Green Frogs are eaten by large Green Frogs and both are eaten by the even larger bullfrogs at the top of the anuran food chain. The apathetic camouflage of Green Frogs makes them consummate sedentary predators, lying in wait for whatever happens to move within range and is small enough to eat. The list includes but is not limited to mollusks, crustaceans, arachnids, insects, fish and other frogs; the wetland is their refectory. They can and do consume vegetation and, in the ultimate act of conservation, their own molted skin. They occupy a critical nexus of the food chain that establishes the ecology of woodland streams.

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Green Frog with distinctive dorsal ridges
The life cycle of the Green Frog is in a sense an allegory of their evolutionary heritage, progressing from an egg, through a fully aquatic piscine intermediate stage that metamorphoses to the amphibian adult. The process starts with mating, the males establishing territories that can be as close as two meters apart that they assiduously defend against intruders. The confrontation starts with vocalized threats and escalates as required to farouche conflict, a unique aggressiveness shared only with the bullfrogs among all other anurans. Females are attracted to the males by their croaks, apparently judging virility according to the qualities of the emitted tones. The males envelope the females in a tight amplexicaul hold (amplexus is Latin for ‘embrace’). Following insemination, between 1,000 and 7,000 eggs are deposited in a frothy film in vegetation along the edges of the stream or pond in a more or less globular mass about one foot in diameter, hatching a few days after deposition into miniscule centimeter-long tadpoles, from the Old English words for ‘toad’ and ‘head” (in England, they are called polliwogs).

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Green Frog aquatic tadpoles

The tadpole to adult metamorphosis is arguably the most radical transformation among all of the vertebrates, surpassed in complexity only by the insects in the entire Animal Kingdom. Tadpoles have no lungs, no jaws, no legs and no eyelids; they consist of a cartilaginous skeleton, aquatic breathing gills, a toothless mouth with a long coiled intestine for plant digestion suitable for their herbivore diet, and a swimming tail for propulsion. The hind limb buds are the first harbinger of change, signaling the development of the signature characteristic of the adult frog; the muscular, webbed swimming and jumping appendages distinguish frogs as prodigious leapers on land and propulsive kickers in water (in addition to providing a dubious delicacy for French cuisine). The smaller forelimbs, which develop internally and emerge fully-formed, signal the onset of the transition to adult. As the lungs are formed to replace the gills, the cartilage vertebra ossifies to a backbone and the mouth forms tearing and chewing teeth to allow for the transition from herbivore to carnivore, the intestine shortened to accommodate the change in diet; the tail is gradually absorbed into the body to form the acaudal rump of the adult frog. While Darwin may consider this one of the “endless forms most beautiful,” the adult frog hardly fits that bill, its pop-eyed, slimy-skin and maw-like mouth a metaphor for execrable ugliness.