Beneath the surface of London’s ponds, a strange drama unfolds—tadpoles with ‘balancers,’ frogs that laugh, and toads with round-tipped tails. But the real mystery? Edible frogs that can’t breed true, and marsh frogs with a taste for noisy romance. Meanwhile, on sun-warmed embankments, adders hunt slow worms, grass snakes stalk frogs, and London’s last surviving reptiles play out their ancient rituals.
Return on 25 May to unravel the tangled love lives of amphibians and the stealthy hunters of the undergrowth.
Article
Amphibians
May is usually the month we start to see tadpoles. The tadpoles of newts tend to be long and thin with projecting adhesive organs or ‘balancers’ at the sides of their heads. They also develop their front legs first, whereas frogs and toads develop their hind legs first. Toad tadpoles can usually be distinguished from frog tadpoles as they have rounder tips to their tails compared to the pointed ones so typical of frogs. They also tend to be black on their upper surface and grey below, compared with the olive colours and speckling typical of frogs. Newt tadpoles tend to look more yellow. Being able to tell Common, Marsh and Edible frog tadpoles apart in the field is more challenging as resorting to dental formulas may be the only answer.
Even the adults are difficult to separate. Common frogs come in a wide range of colours from albino, yellowish, brownish through to dark green. Edible frogs are noted for being a vivid bright green which common frogs never are. Marsh frogs range from brown to green, in the same way that common frogs do, but lack the black patch that common frogs have behind their eyes. Marsh frogs are also usually larger, up to fifteen centimetres in length, with distinctly pointed snouts. When Marsh frogs are ‘singing’ they have large vocal sacs and are quite noisy, hence their other name of ‘laughing’ frog.
The sexual life of marsh frogs and edible frogs is quite a complicated affair. Edible frogs Rana esculenta are produced when male pool frogs R. lessonae mate with female marsh frogs R. ribunda. When edible frogs mate with each other they only produce female marsh frogs. Luckily, they prefer to mate with pool frogs, in which case their progeny are all edible frogs. Consequently, the difference between a marsh frog and an edible frog can at best be slight. When they both hold their hind legs up close to their body, if their heels overlap it is likely to be a marsh frog and if they do not, an edible frog. Luckily, all three can be found on Crane Park Island reserve, where they are capable of creating quiet a chorus.
Reptiles
All our reptiles are now active and still mating. The adder is the first to stop chasing females usually in mid May. The rest may be encountered coiled together or chasing each other the whole of the month. They are all feeding, surprisingly, taking quite different prey. Slow worms are happy devouring snails and slugs and sucking the contents of the occasional earthworm before swallowing it. Common lizards prefer insects and spiders, but will also suck earthworms, but prefer not to swallow them. Grass snakes have a diet consisting almost entirely of frogs, toads and newts, even eating their tadpoles and eggs. Adders are the most catholic in their taste eating mice, voles, shrews, nestlings, eggs, most of our amphibians and even slow worms.
In London, Slow worms are our most abundant reptile, being well distributed on endless railway embankments. Grass snakes are second in numbers, preferring undisturbed grassy areas close to water, as well as the edges of golf courses and gravel pits. Common lizards come next, with small numbers being found again on railway sidings, mainly in South East London. Adders are our least common reptile, being virtually extinct except for one or two locations on south London heaths.
