This is a very good month for talking about frogs and tadpoles. With the weather warming and garden ponds coming back to life and the last of the frogspawn lying thick and glutinous on the water,  the first of this year’s tadpoles are already swimming among the weeds. It is a sight that never fails to cause a stir of excitement in our house.

There is only one species of frog that you are likely to see in the UK and that is the Common Frog.  This species can be found all over Eurasia from the Arctic Circle all the way down to Mediterranean and in pockets as far east as Japan. The only other native frog that can be found in Britain, the very rare Pool Frog Pelophylax lessonae is confined to Norfolk. The common frog, though, can be found in parks, gardens and wild places all over the British Isles.

 

Frogs spend much of the colder months of the year buried in mud at the bottom of ponds, occasionally emerging to swim around or make a foray into the undergrowth if the weather warms up sufficiently. They don’t hibernate, but they do slow their body rhythm and their activity to be able to cope with the scarce food resources and cold temperatures of winter.

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Along with other amphibians and reptiles, frogs don’t have a regular breathing rhythm like we do. When inactive a frog can take enough air into its lungs through its skin, whether it is deep under water, immersed in mud or out in the air and in this way a frog can happily hole up at the bottom of a pond for weeks or months at a time without ever coming to the surface.  Oxygen from the air and water is easily absorbed into the skin through a mass of capillaries and is transfered directly into the blood stream without needing to be processed by the lungs.  Waste gases such as carbon dioxide are expelled in the same way. When out of the water a frog can gulp air down into its lungs as you would expect, or it can breathe through its nostrils, drawing air over the moist lining of the mouth which can extract oxygen, just like its skin.

The life cycle of the frog, so well loved by primary school teachers, is fascinating to revisit.  In early spring, as early as January if the weather is mild, male and female frogs arise from their winter slumbers and begin to look for mating opportunities near ponds and lakes. Females are attracted to the males who croak the loudest and head towards any body of still water where males may  be found. The female, not infrequently with a male already riding piggyback, will enter the water and lay a clutch of about 2000 eggs. The male, clutching the female in a mating embrace, quickly fertilizes the eggs as they are released, then goes off in search of another mate.

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The fertilized eggs, in their protective jelly bags, will grow and develop until, after about four weeks, they will hatch out into tadpoles. These tiny fish-like creatures breathe through external gills which can be seen on either side of their heads, and they feed on algae, tiny water plants and any decaying animal matter they may come across. After another four weeks the gills are reabsorbed into the tadpole’s body and they begin to breathe through their skin as adults do. At about 7 weeks their hind legs have grown and by 10 weeks their front legs are coming through, their tales are beginning to shrink and be reabsorbed and they are beginning to develop lungs, and by only 12 weeks the little tadpoles have finished their metamorphoses and have turned into perfect little miniature frogs. These froglets are now able to leave the pond and hunt for tiny slugs and insects in the vegetation around the pond. 

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Ever seen a screaming frog? Frogs don’t have much in the way of defence – they don’t even have the benefit of being able to excrete a foul tasting poison like toads can -  but they can offer quite a lot in the way of a deterrent by employing the element of surprise  Not being contained within a diaphragm, as our lungs are, a frog can gulp enough air into its lungs to inflate and expand its entire torso. At the same time it leaps towards its attacker with its mouth wide open and uttering a blood curdling scream by forcing the air out under pressure. The first time I saw and heard a frog screaming while leaping towards me it made me jump back involuntarily, so I can well understand a fox or cat turning tale at such an encounter.