Friday Fellow: European Common Frog

by Piter Kehoma Boll

We are about to reach 300 Friday Fellows and only one amphibian has been presented until now. So I guess it is time to present at last an anuran species and, although there are many interesting species all around the world, I decided to talk about the most common, or at least most known, species, the European common frog, Rana temporaria.

Found across Eurasia, this species is, one could say, the type-species of the anuran amphibians. It still has the very same name that Linnaeus has given to it back in 1758, when all other anurans were also put in the genus Rana.

A dark-brown specimen in the UK.

As most true frogs, the European common frog is a semiaquatic species, with adults living their whole life in the water or damp places near waterbodies, especially ponds and marshes. They hibernate during the coldest months of the year, but some populations can remain considerably active even when water is at temperatures very close to freezing. Their skin can vary considerably in color from olive green to several shades of brown and gray, and, in some rare cases, they can even be black or red. They have the ability to adjust their color to their surroundings, thus increasing their camouflage ability. There are also irregular dark blotches distributed across the body, especially on the limbs and flanks.

A yellowish specimen from Spain on a human hand for size comparison.

Adult specimens measure from 6 to 9 cm in length, with females being slightly larger than males. They feed on a variety of invertebrates, including arthropods, gastropods, worms and almost anything small that crawls near them.

In spring, both males and females start to produce sex cells and prepare for mating. They congregate in ponds in large groups and males compete for females through very loud vocalizations and usually those able to produce the loudest and longest calls are preferred. When a female approaches a selected male, he will try to grab her, moving over her, and holding her with his front legs grasping her under her own forelegs. An enarlged, swollen, area on the male’s thumbs, known as the nuptial pad, helps him to hold the female. If other males try to graps her, he kicks them away. The female eventually will release her eggs and he will pour his sperm over them as they are released.

A couple in Switzerland seeking for a nice wet room to make love.

The eggs form jelly-like clusters that float on water and neither the female nor the male will take care of them. The eggs develop and hatch at different rates, depending on temperature. The higher the temperature, the faster the development, and the same happens with tadpoles as they hatch and grow. Newly hatched tadpoles are mostly herbivorous, feeding on algae, but become fully carnivorous with time, eating any small animals they can find, including other, smaller tadpoles.

Lots of eggs floating on a pond in Italy.

The European common frog is usually not exploited by humans as a resource. It is not edible, or at last not often eaten, as far as I can say. It is, however, a very well studied species due to its common occurrence in human-inhabited areas across Eurasia, so that there is a lot of data available about its ecology, genetic diversity, behavior and much more. Its populations are affected by human activities nonetheless, especially urbanization, which causes habitat barriers, and pollution. Nevertheless, it is not a threatened species at the moment.

Tadpoles in Italy.

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References:

Decout, S., Manel, S., Miaud, C., & Luque, S. (2012). Integrative approach for landscape-based graph connectivity analysis: a case study with the common frog (Rana temporaria) in human-dominated landscapes. Landscape ecology27(2), 267-279. https://doi.org/10.1007/s10980-011-9694-z

Wikipedia. Common frog. Available at < https://en.wikipedia.org/wiki/Common_frog >. Access on 15 July 2021.

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