This hybrid form displays a morphology intermediate between its parental species, the Pool Frog (Rana lessonae) and the Marsh Frog (R. ridibunda). This trait is revealed, in particular, in the values of some characters having identification value. When the shins are positioned perpendicularly to the body axis, the heels contact. Inner metatarsal tubercle 1.73-2.89 times shorter than the first toe. Dorsal coloration greyish-green, olive-green or green with dark spots which vary in size and number. Light middorsal line from snout to cloaca usually present. No temporal spot. Belly light, usually with dark spots. Male vocal sacs positioned behind the mouth angles and are grey.
 
Rana esculenta is the hybrid of R. ridibundaand R. lessonae. Together with diploid individuals, hybrid populations may also contain triploids. Great variability in the population systems of these three forms exists within the range, where the hybrid (or either parental) form may coexist or not coexist with the both (or any) other forms. Genetic, ecological and behavioral studies in these frogs are in progress.

This species ranges throughout most of western, central and eastern Europe; populations are largely sympatric with populations of the parental species. It is absent from much of Scandinavia (although present in Denmark and southern most Sweden [it is unclear as to whether or not the Swedish populations are relicts or introductions]). In Italy it is present only with certainty in the River Po plain. The species has been introduced to the United Kingdom [not mapped here] and to Spain at Villasbuenas de Gata, Cáceres and unspecified localities in Galicia, Cataluña and Comunidad Valenciana. It is generally a lowland taxon which might occur up to approximately 1,550m asl.

The range of this form is almost identical to that of R. lessonae. It should be observed, however, that in the eastern part of the distribution of R. lessonae (in the Volga-Kama region in Central Russia), the latter species is sympatric with R. ridibunda at many sites but R. esculenta is very rare. At the same time, R. esculenta occurs in Estonia where one of the parental species, R. ridibunda, is considered to be extinct. It should be observed that it is not easy to distinguish the hybrid form and its parental species for inexperienced observers, so some records of R. esculenta require further verification.

In general, R. esculenta is very similar to R. lessonae in ecology but it also occurs in some habitats of R. ridibunda. As a rule, it lives in habitats which are intermediate in their parameters between the two parental species: floodland lakes, overgrown ponds, river pools, channels, ditches etc. However, R. esculenta avoids very large pools with flowing water and does not enter dense forests.

Habitat and Ecology

Systems

• Terrestrial
• Freshwater

In Great Britain and/or Ireland:
Animal / predator
Rana esculenta is predator of imago of Donacia clavipes

Maximum longevity: 12 years (wild) Observations: In the wild, these animals may live up to 12 years (Smirina 1994).

Feet used for powerful swimming: true frogs
 

The webbed back feet of true frogs are used to swim by pushing back against the water creating vortex rings.

   
  "Frogs propel themselves by kicking water backwards using a synchronised extension of their hind limbs and webbed feet. To understand this propulsion process, we quantified the water movements and displacements resulting from swimming in the green frog Rana esculenta, applying digital particle image velocimetry (DPIV) to the frog’s wake.

"The wake showed two vortex rings left behind by the two feet. The rings appeared to be elliptic in planform, urging for correction of the observed ring radii. The rings’ long and short axes (average ratio 1.75:1) were about the same size as the length and width of the propelling frog foot and the ellipsoid mass of water accelerated with it. Average thrust forces were derived from the vortex rings, assuming all propulsive energy to be compiled in the rings. The calculated average forces (Fav=0.10±0.04·N) were in close agreement with our parallel study applying a momentum–impulse approach to water displacements during the leg extension phase.

"We did not find any support for previously assumed propulsion enhancement mechanisms. The feet do not clap together at the end of the power stroke and no ‘wedgeaction’ jetting is observed. Each foot accelerates its own water mantle, ending up in a separate vortex ring without interference by the other leg." (Stamhuis and Nauwelaerts 2005:1445)

  Learn more about this functional adaptation.

Population

Population Trend

Rana esculenta appears to be relatively rare in the south-eastern and eastern parts of its range. Hibernation occurs from September-October to March-May. The mode of hibernation resembles that in coexisting parental species: in water (when coexisting with R. ridibunda) or on land (with R. lessonae). Breeding calls in R. esculenta are more similar to those in R. lessonae than R. ridibunda. The same concerns some other behavioral and ecological traits.

Major Threats

Conservation Actions

The species occurs not only in natural but also in anthropogenically altered habitats.