“I’d kiss a frog even if there was no promise of a Prince Charming popping out of it. I love frogs.” – Cameron Diaz
There are more than 5,000 known species of frog and new ones turn up all the time: 100 were identified in Sri Lanka in 2002 alone.
Last year, a new frog that changes colour as it gets older was found in south-western Papua New Guinea. The juvenile Oreophryne ezra frog is shiny black with yellow spots and black eyes, whereas the mature adult is pale peach with intense blue eyes. No one knows why it changes.
A 2008 discovery from the west of the island is a species of Litoria tree frog dubbed “Pinocchio” by the expedition who found it, because the male has a pointy nose that inflates and points upwards during its loud mating call but deflates and points down while it’s at rest.
Almost all the noise made by frogs is males advertising themselves to mates. They croak, snore, grunt, trill, cluck, chirp, ring, whoop, whistle and growl, and these calls operate rather like radio stations: each species selects its own frequency. So what we hear – a forest or pond full of competing froggy racket – is much less distracting to the lady frogs, who only tune in to their own species’ calls.
Frogs even have regional accents. The rare Northern pool frog (Rana lessonae), a native of the fens, has its own unique Norfolk-accented croak. When it became extinct in England in the Nineties, it was reintroduced using a closely related Swedish population identified as having the same low-frequency croak.
Practically the only noise a female frog makes is the release call she uses when she’s had enough of the amplexus (amb- around + plectere to braid) most frogs and toads use as part of their mating.
The male uses his arms to attach himself to the female: some species even grow sticky “nuptial pads” to lock themselves in place long enough for the female’s eggs to emerge.This can take several days, and sometimes several males join in, often with disastrous results as the resulting weight can drown the female.
Occasionally, a lovestruck male will attach himself to an old boot or a dead fish by mistake.
Frogs once provided our most accurate pregnancy test. The African clawed frog (Xenopus laevis) ovulates if injected with the urine from a pregnant woman (the hormone chorionic gonadotrophin is the active ingredient).
A 99.9 per cent accurate result is returned within 5-18 hours and a single specimen can be used many times.
The original tests were done in Cape Town in 1931 and through the Forties and Fifties many of the world’s hospitals kept these frogs as living pregnancy-testing kits. Inevitably, some escaped and there are now wild populations in California, South America and south Wales.
The trade in African frogs is thought to be one of the causes of the global outbreak of chytridio-mycosis, the fungal disease that, along with climate change and habitat destruction, is causing frogs to disappear at an alarming rate. Almost a third of all frog species are on the danger list.
This may be a tragedy for the human race as well. Frog toxins — such as cocaine, nicotine, codeine, caffeine and quinine – are alkaloids that can be transformed into drugs that may cure everything from Alzheimer’s disease to cancer.
The Ecuadorean tree frog (Epipedobates tricolor) yields a painkiller 200 times more powerful than morphine.
The world’s most poisonous frog, the Golden poison dart frog (Phyllobates terribilis), provides another, which is 600 times as powerful. Both are non-addictive, with no side-effects.
Inside other frogs may be muscle relaxants and heart stimulants, as well as cures for strokes, bacterial infections and depression.
The French eat about 4,000 tons of frogs’ legs a year, equivalent to 60-80 million frogs. Since edible frogs are now a protected species in France, frogs’ legs are imported from Indonesia.
Frog-eating isn’t the origin of the “frog” nickname. It was first used by the British about the Dutch, our implacable enemies in the 17th century. Presumably, they were termed “frogs” because they lived on marshland. When we resumed our traditional hostilities with the French in the 18th century, the insult “frog” was transferred across.
Frogs and toads
There’s no strict difference between frogs and toads. Toads are spread across five families of the Anura (“no tail”) genus, which also includes frogs. Generally speaking, toads crawl instead of hop, have rough skin, are fat-bodied, and live drier lives than frogs. Most frogs have teeth; most toads don’t. In Britain we have two toads – the quite rare Natterjack (Epidalea calamita) and the quite common Common (Bufo bufo). Natterjacks are a protected species, but the common toad has only one legal right: it’s against the law to sell them.
Tadpole means “toad-head” in Old English (tadde “toad” + pol “head”).