Category Archives: London Amphibians

Tadpoles Emerging

Tadpoles emerging 002As if they all received the signal at the same time, the tadpoles in my pond are emerging from the frogspawn. The surface of the water is a-wriggle with tiny tails as they try to break free from the confiness of the jelly that’s held them for the past few weeks.

The membrane that surrounds each egg allows the water from the pond to pass through it – this means that the embryos develop at the same rate, and will all hatch at the same time. There is safety in numbers for such little creatures, who at this stage can be eaten by anything from dragonfly larvae to diving beetles to water boatmen. It also helps to prevent cannibalism, which tadpoles are not averse to once they develop legs and become carnivorous.

In the film, you can see that there are some water snails hanging about – these have probably helped by cleaning any algae that started to grow on the frogspawn. In the bottom right-hand corner, though, there is a pond-skater – although it can’t eat a whole tadpole, it is quite capable of puncturing one and injuring it. Life is hard for frogs, right from the start.

Good luck, tadpoles. Out of all of this seething mass, one in a thousand will return next year to breed. The rest will sustain a whole generation of dragonflies and other aquatic insects. Nature is abundant, but rarely wasteful.

Goings On in the Pond

Male frog waiting for the females to arrive

Male frog waiting for the females to arrive

A week ago, as I headed out to the shed, I heard the smallest of croaks coming from the pond. Just a single ‘ribbit’ and then silence. But that little sound was as much a harbinger of spring as all the crocuses erupting into flower. For it meant that the frogs were waking up.

At first, the males appear. They are smaller than the females, and have spent all winter in the silt at the bottom of the pond. They can breathe through their skin if they are not very active, but as the days lengthen and the temperature increases, they need to come to the surface to breathe. The second sign of spring is the increased interest that the local cats show in the pond. All winter they’ve ignored it, but now they can sit and stare at it for hours. Jarvis is a newcomer: a very fine cat and (fortunately) not one to get his paws wet if he can help it.

Jarvis waiting to play Whack a Frog

Jarvis pretending that he isn’t interested in the frogs. Not at all.

The males are hyped-up. Their hormones start to change in the autumn, so that they are ready for action the instant the weather gets warm enough. While they are waiting, they sing to attract the females, and sometimes attempt to mate with other males. The males make a very particular grunting noise if propositioned in this way, the frog equivalent of ‘try that again and I’ll wallop you’. Once the female has laid her eggs, she will make exactly the same sound if a male tries to grab her again.

Male frog hanging around

Male frog hanging around

Eventually the females turn up – in my garden, females arrived within a day of the males’ serenade. They seem to be able to find their way back to their natal pond by smell, as the combination of the particular plants that grow there seems to be unique for each water body. Once the females arrive, there is a thrashing, roiling orgy of froggy copulation. The males hang on to the females, clasping their front feet together under her armpits in a grasp called ‘amplexus’. This can last for anything from a few hours to several days. Even capturing the frogs for a quick attempt at a picture is not enough to put them off their stride.

Two frogs in amplexus, refusing to be separated even when the paparazzi arrive

Two frogs in amplexus, refusing to be separated even when the paparazzi arrive

The purpose of all of this is so that when the female lays her eggs, the male can fertilize them right away, without any other male getting a chance to do the same. Female frogs are very swollen prior to egg-laying, and look a little saggy afterwards, and no wonder – the mass of eggs being ejected is enormous for such a small animal.

Frogs mating at the edge of a mass of frogspawn

Frogs mating at the edge of a mass of frogspawn

In my pond, the frogs have chosen to lay all of their eggs in the shallow end, where the water barely covers the pebbles. The sun warms the eggs, and hastens the development of the tadpoles inside. Each clump of frogspawn represents one mating, and can contain between a thousand and four thousand eggs.

Frogspawn so far

Frogspawn so far

Frogs are invaluable for the garden. Up to twenty-five percent of their diet is snails and slugs, with caterpillars, gnats, and other insects making up the rest. However, the garden is not always good for frogs. Research shows that they are extremely vulnerable to pesticides, which they both ingest by eating affected insects, and absorb through their skins, which are delicate and porous. Not only are they directly poisoned by these substances, but they also affect the immune system, making the frog more prone to fungal diseases and parasites. It seems ironic that our use of artificial pesticides is killing one of the creatures most able to help the gardener.

The Gardener's Friend

The Gardener’s Friend