Tadpoles

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Tadpoles
© Paul Keene (Avico Ltd)

Almost everyone will be familiar with the small wriggling beasts from which both frogs and toads will develop. Frogs lay their spawn before toads and the eggs may have become tadpoles by March in warmer parts of the country. Elsewhere this process may not happen until late spring. Tadpole growth rates are influenced by overcrowding and if too many tadpoles are present in a pond, competition for food may mean that only the larger tadpoles may develop into frogs before the summer ends. The remaining tadpoles usually die during the winter.

There are between 1, 000 and 2, 000 eggs in each clump of frogspawn, while a common toad spawn 'string' may contain as many as 5, 000 eggs. In each case, only a handful of offspring will reach adulthood, the remainder providing food for a wide variety of predators including diving beetles, dragonfly larvae, fish, adult newts, grass snakes and even birds. Toad tadpoles have a distasteful skin and are not eaten by many fish or by the smaller species of newt.

The respective appearance and behaviour of the tadpoles of frogs and toads differs greatly. Frog tadpoles are brown, speckled with gold while those of toads are much darker. As frog tadpoles grow they embark on a fairly solitary lifestyle, whereas toad tadpoles are far more sociable and swim in obvious black shoals until they turn into toadlets.

Tiny froglets and toadlets leave their breeding pools in the summer, seeking shelter in humid places under stones or among dense vegetation. They remain very vulnerable to predators, as even blackbirds will turn their attention away from worms in the lawn if there are easier pickings at the water's edge.

Young newts are very different creatures. Adult females lay up to 300 eggs, each one wrapped individually in the leaf of a water weed. The newly hatched newt is tiny, resembling a mere sliver of glass. Unlike frog and toad tadpoles, it is carnivorous from the outset. The forelimbs develop first. The larvae of smooth newts spend much of their life hidden among vegetation, changing into adults when they are about 25cm long. Great crested newt larvae are much larger, approaching the length of a small adult smooth newt. They have more elongated fingers and toes, a long tail filament and swim about in the open water feeding on small animals such as water fleas. This behaviour makes them more susceptible to predation by fish.

Newt larvae may sometimes develop slowly and not metamorphose until the spring following the year when the eggs were laid.

Plants

Brooklime, Common water-starwort, Fringed water-lily, Frogbit, Ivy-leaved duckweed, Rigid hornwort, Spiked water-milfoil, Water-lily, Water-violet, Whorled water-milfoil

Predators

Common backswimmer, Common darter dragonfly, Dragonflies and damselflies, Four-spotted chaser dragonfly, Grass snake, Great crested newt, Great diving beetle, Great pond snail, Smooth newt, Southern hawker dragonfly, Water scorpion