Frogs: Inside Their Remarkable World, Ellin Beltz (2005)

Everyone say “eye”. Because I think that is one of the most important reasons that frogs and toads are so endearing. Their large eyes and their large mouths make them seem full of character and full of interest in the world. Their four limbs and plumpness are important too, I think, and I suspect that looking at them activates some of the same regions of the brain as looking at a baby does. All that would certainly help explain why we like them. The Californian herpetologist Ellin Beltz doesn’t spend long examining the roots of the human affection for and interest in the batrachians, as frogs and toads are called. “Is it perhaps that frogs look and act rather like people?” she asks and then gets on with the science. But she herself is obviously a dedicated batrachophile and she’s written an interesting and exhaustive introduction to what is indeed a remarkable world. There are frogs smaller than a human fingernail, like Psyllophryne didactyla, the gold frog of southeastern Brazil, and frogs larger than a human head. Or one species larger than some heads, anyway: Conraua goliath, the goliath frog of Cameroon. There are also frogs, the Malaysian Rhacophorus spp.,* that fly, or glide, at least, on the extended webbing between their toes, and frogs that literally stick around for sex: “males of the genus Breviceps from southern Africa” have very “short front legs” and “use special skin secretions to glue themselves onto the females” (pg. 149). Elsewhere, the Australian desert spadefoot toad, Notaden nichollsi, uses a “smelly skin secretion” to ward off predators (pg. 58).

(*Sp. = species, singular; spp. = species, plural.)

That species isn’t very dangerous, but the much smaller poison-arrow frogs of South America definitely are: “the golden dart frog, Phyllobates terribilis, is credited with producing ‘the most toxic naturally occurring substance’ ” (pg. 147). In captivity, deprived of the wild food from which they manufacture their toxins, the poison-arrow frogs are harmless, but their remarkable colours remain: they look like harlequins in all shades of the rainbow. Whether these rainbow frogs are also raines beaux, or “beautiful frogs”, as they might be called in French, is a matter of taste, but some frogs definitely are beautiful. So are some toads: the male golden toad, Bufo periglenes, is a vivid golden-orange. Or rather, was: it was once a tourist attraction as it swarmed “out to mate in great congregations” in the Monteverde Cloud Forest Reserve in Costa Rica, but “photographs seem to be all that remains of this exquisite amphibian” (pg. 43). Yes, the ugliness in this book isn’t supplied only by the villainous-looking cane toad, Bufo marinus, which has been munching and poisoning its way through Australia’s native wildlife since it was foolishly introduced there in 1935. There’s also ugliness in the story of what is happening to the world’s amphibians. They’ve been disappearing everywhere and most of chapter four, “Environment & Adaptation”, is given over to the threats they face from pollution, bacteria, viruses, and various fungi, including the chytrid fungus responsible for “chytridiomycosis, a fatal fungus disease that leads to thickening and sloughing of the skin and death by unknown causes” (pg. 118).

African clawed frogs, Xenopus spp., are “asymptomatic carriers” of chytrid fungus. Because they were once used in pregnancy tests, they have been introduced all over the world and may have helped the fungus spread. However, the ever-growing human population is perhaps the greatest threat to the survival of wild amphibia, as it is to fauna and flora in general. More people mean more roads and more cars, for example:

Roadkill numbers are immense. Frogs don’t even have to be hit by a vehicle; the force of its passing can literally suck them inside out. Hundreds of flattened and inverted corpses lie roadways on rainy nights. (pg. 121)

Some species may be disappearing without ever being recorded. Perhaps the strangest and unfroggy-est frog in this book is Nakisakabatrachus sahyadrensis, the Kerala purple frog of southern India, which has tiny eyes and dark, leathery skin. It lives underground most of the year and was only described by scientists in 2003. Its tiny eyes are part of its adaptation to underground life. Eyes are a guide to ecology in other ways: a batrachian’s angle of vision is a clue to its edibility. Frogs, whose eyes are usually positioned so they can see both ahead and behind, are edible and fear predators. Toads, which usually can’t see behind themselves, are inedible and don’t fear predators. I can remember once picking up a tiny toadlet, or juvenile toad, and feeling my fingers sting from the secretions it released. Among Beltz’ personal anecdotes in this book is one about what happened when she and a colleague found a Couch’s spadefoot toad, Scaphiopus couchii, on the U.S.-Mexico border:

It was drizzling, and I brought the toad into the car for a good identification. We were paging through the field guide and put on the defoggers to clear the windows when we were overcome by a wave of noxious vapor emitted by the toad. It was like teargas and we exploded out of the car, put the toad into a ditch and tried to air out the car. Whatever toxin the toad let loose that night, I was down for 24 hours, sleeping with runny eyes and all the symptoms of a major cold. My colleague was similarly affected. Other reports of noxious fumes from southwestern toads have been [made]. (“Frog Miscellany”, pg. 149)

Stories like that are part of what makes this such an enjoyable book and although, at 175 pages with lots of large photos, it’s too brief to explore thoroughly all the biological topics it raises, there are pointers to some interesting aspects of evolution – and mathematics. Try this description of the Eastern spadefoot, Scaphiopus holbrookii, and plains spadefoot, Spea bombifrons, which live in deserts in North America:

When the rains fall, they congregate at temporary pools to breed. It takes the eggs two weeks to hatch into tadpoles. At this point, more rain is needed; otherwise the pools dry up and the plant-eating tadpoles die. Some tadpoles become cannibalistic under these harsh conditions, permitting some individuals to survive long enough to transform into frogs by eating the bodies of their herbivorous relatives. (ch. 2, “Frog Families”, pg. 37)

Consider the evolutionary mathematics of this cannibalism. It’s easy to understand genes instructing an individual to eat. Less easy to understand are genes that might instruct an individual to let itself be eaten. But the tadpoles in a temporary pool can be seen as a kind of super-organism. The super-organism initially has many mouths to turn algae and so on into tadpole-flesh. Then, as the pool shrinks, the super-organism begins to eat itself, having exploited the resources of the pool with maximum efficiency. It’s possible there is even a class of tadpole that exists to put on flesh fast and then be eaten by its siblings. It would never breed, but evolutionarily speaking that behaviour would be no more paradoxical than the sterile workers among ants, bees and wasps. Or the juvenile birds that let themselves starve to death in an over-crowded, underfed nest. The apparently suicidal genes of a cannibalized tadpole or sterile worker or starved nestling do not survive in that non-breeding individual, but they promote behaviour that enables unactivated copies of themselves to survive better in other individuals – as Richard Dawkins explains in The Blind Watchmaker (1986).

Swimming in another kind of pool is responsible for other evolved features in batrachians: their sometimes vivid colours or cunning camouflage. For millions of years, images of batrachians have been created in the chemical sludge of predators’ brains. And so, like snakes and wasps, batrachians signal their toxicity with colour. Or use colour to disguise their outlines or blend into the background. But batrachians are also like octopuses and other cephalopods: they can change their colour using special structures in their skin called chromatophores. One of the briefest but most interesting sections in this book discusses this shade-shifting and the cells responsible for it: the melanophores (responsible for black and brown colouration), xanthophores (yellow), erythrophores (red and orange), and iridophores (responsible for iridescence in the poison-arrow frogs). But what is briefly mentioned is extensively illustrated: almost every page has one or more colourful photographs of frogs and toads, usually in what appears to be their natural habitat.

There are also diagrams of batrachian anatomy and evolutionary relationships and pictures of art and sculpture in chapter five, “Frogs in Myth and Culture”. You’ll learn in the evolutionary discussions that toads aren’t a distinct group, because they don’t have a single common ancestor distinguishing them from frogs. But they look different to us and chapter five says that they were sacred to Heqet, the Egyptian goddess of childbirth and fertility. She’s depicted with an almost scientifically precise green toad, or Bufo viridis, on an ivory obstetric wand found near Thebes and dating from “around 2000 to 1700 BCE” (pg. 131). That “BCE”, like the “humanmade objects” mentioned on page 47, is a reminder that Ellin Beltz is a modern, and politically correct, American, unlike a Californian born in the Victorian era whose absence can’t, alas, be called a flaw in this book. The Auburn writer Clark Ashton Smith (1893-1961) and his interplanetary toad-god Tsathoggua and man-slaying toad-witch Mère “Mother of Toads” Antoinette aren’t famous and Beltz may never have heard of them. Instead, she discusses Shakespeare and the three toad-toxin-brewing witches of Macbeth (1611), Mark Twain and “The Celebrated Jumping Frog of Calaveras County” (1867), and Kenneth Graham and Toad of Toad Hall from Wind in the Willows (1908).

In short, she covers all the batrachian bases, from biology to books by way of batrachophagous bats and a bee-eating Bufo japonicus. The batrachophage, or frog-eater, is the fringe-lipped bat, Trachops cirrhosus of Central America, which tracks its prey by homing in on their calls. And here’s another acoustic anecdote to end on, demonstrating that Hollywood’s hegemony is partly herpetological:

Chorus frogs, Pseudacris spp., include the Pacific treefrog, Pseudacris regilla, the “ribbet frog” known to every movie fan. At some time in the early days of talkies, someone recorded frogs in a pond, probably near the famous Hollywood sign. The same audio loop is used over and over again in movies, leading to hysteria among amphibian researchers who hear “ribbet” in darkest Africa, South America and Australia… The Pacific treefrog is actually restricted to the western edge of North America. (ch. 2, “Frog Families”, pg. 49)