Rana temporaria, the Common Frog

The Common Frog Rana temporaria, rana meaning ‘to gaze’, and temporaria meaning ‘temporary’, spends winter hibernating in frost-free hideaways such as under tree stumps, in stacks of logs, or in stone walls where they will enter a torpor until the following spring. They emerge around February and spawn around March, the tadpoles hatching and growing from April to May and metamorphosing into froglets around June which is when they leave their pond.

Hibernaculum

When adult frogs emerge from their hibernaculum (one of my favourite words!) they travel to congregate at various breeding sites, covering up to half a mile to find a pond or splash where they will gather in large numbers, they travel to the same breeding site year after year and it is theorised that they can recognise the site from its smell.

Males always arrive first and will strike up a chorus of loud croaking to attract females but frogs do not have any elegant courtship rituals, the male just simply grabs the nearest female as she arrives at the spawning site. The female Frog will release over 2000 eggs during spawning and after the male has fertilised them they will both leave the pond, with the male going to seek another mate straight away.

Tadpoles

The tadpole first lives off the jelly of the frogspawn and hatches after about 10 days, it then uses special sticky organs to fasten to plants in the pond. At this early stage they have no mouth, and until its mouthparts grow it will feed on an internal yolk-sac, at around 2 days old it will develop mouthparts, as well as gills and eyes and will start to swim around the pond to feed on algae. They can be distinguished from the tadpoles of the Common Toad by the gold speckles they seem to have all over their jet black skin.

Over the next month it will develop further until it starts to grow hind legs, at this stage it will have also grown proper lungs instead of gills like a fish and then has to swim to the surface of the water to gulp air. The tadpole will have developed fleshy lips with rows of teeth which they will use to rasp away at water plants and at 7 weeks old it will eat insects and even other tadpoles. In very cold years tadpoles might hold off maturing further until the next spring and may over winter as tadpoles.

Froglets

The point at which a tadpole can be called a froglet is when they are about 10 weeks old and have started to grow front legs, 4 weeks later, 14 weeks after they emerged from the frogspawn they will have lost their tail entirely, at this stage they will have moved away from the pond to the safety of nearby grass.

By autumn the froglet will have doubled in size though it will take 3 years to be fully mature, and they can live for up to 9 years. Adult frogs become adept predators but are still very vulnerable to being preyed on themselves, so have evolved several features over the millions of years they have been around which make them both quick at catching food and quick at avoiding becoming food themselves.

Predator and Prey

Their large eyes bulge out of the top of their head so the frog can see in a wide radius and above too, they are very sensitive to movement but also fragile so when they leap they draw eyes their back into their sockets to protect them from being damaged. Frogs also have very good hearing, with large ear drums placed just behind their eyes.

Being amphibians frogs also have adaptations which enable them to hide underwater; they can breathe through their skin for one thing which means they can remain there indefinitely and their skin is camouflaged with dark bars and streams across a green background.

This background colour can be changed as well, with the frog having the ability to make it darker or lighter to match the bottom of the pond, lastly its legs are famously long and muscular so it can jump or swim quickly away from danger or towards prey, with webbing between its long toes helping it to be an excellent swimmer.

The predators of frogs include Hedgehogs, Rats, Otters, Buzzards, Adders, Mink and Herons and they are most vulnerable when breeding. Every now and then a mysterious substance called ‘Bog-snot’ or ‘Star jelly’ is found which was long thought by scientists to be frogspawn that Herons had regurgitated but is now thought to be a type of fungus.

Sometimes you can find frogspawn which does appear to have been brought up by Herons and alongside ponds and streams you will occasionally find bits of frogs and toads which mink will leave behind as they do kill more prey than they need to.

Frogs themselves hunt anything they can fit in their mouths, just like Toads they are voracious and not fussy, using their eyes to force prey down into their stomach, which is why they close their eyes when swallowing. Slugs, worms, larvae, beetles and spiders will be caught, although they rarely catch aquatic prey so can live alongside fish. They will also eat their own skin when they moult.

Encouraging frogs

To encourage Frogs to an area a clean body of water is needed and they required certain features to keep them happy, cover from predators is one important consideration as is having an area of bank which is shallow enough for them to use to get in and out of the water. They also need places to hibernate nearby if you want them to return next year.

If you do find any frogspawn please leave it be as it is very fragile and sensitive to handling, also frogs are currently at risk from a deadly disease caused Ranavirus, so even if you think you might be helping by removing frogspawn and placing it elsewhere you might be spreading Ranavirus around the country instead.

Furuike ya
kawazu tobikomu
mizu no oto

(Basho)

A B-H