Simon Barnes is a missionary and his new book for children, Planet Zoo, is an unabashed evangelical tract. Its purpose, he says cheerfully, is to save the planet. He’s also a storyteller, explorer, naturalist and award-winning writer. Who better to spread the conservation message?

Planet Zoo, subtitled “100 Animals We Can’t Afford to Lose”, is a modern-day bestiary of species on the brink of extinction: “weird, amazing, wonderful, ugly, beautiful, enormous, tiny - and nearly dead.” Species 100 is humankind: the only animal with the potential to destroy itself and the planet. But this is no doom-laden sermon; it’s a life-affirming account of the breathtaking beauty and diversity of the natural world: “the endlessly different ways in which life on Earth happens.” If biodiversity is one of its themes, “not giving up” is the other.

Simon Barnes has great faith in the next generation. Planet Zoo was originally planned for adults - “a kind of Silent Spring for the millennium”, but that book is still to be written. It was the eight-year-old daughter of a neighbour who gave him the idea for a children’s book when she persuaded her father to exchange his old car for one using unleaded petrol. “I realised it was children who could make the difference,” says Barnes. “She could see the point.”

In choosing 100 species out of the countless others still just hanging on, Barnes has gone for the weird and wonderful; “animals with fabulous stories to tell”, which will inspire children and show them that the world is more amazing than they ever imagined or ever could imagine. The glamour species are all here: tiger, polar bear, leopard, and elephant; but so are the distinctly unglamorous: the Australian ant; the pygmy hog-sucking louse; the Iowa Pleistocene snail and the kerry slug. “It is, I know, hard to love a slug,” admits Barnes. “But conservation is not a matter of taste.” Other extraordinary rarities selected from the Red Data books of the International Union for Nature Conservation, include the kakapo - the flightless parrot, which was almost wiped out when New Zealand settlers introduced cats, rats and stoats; and the Yangtze river dolphin - perfectly adapted to an environment of liquid mud, until motor boats and fishing nets reduced their numbers to around 300. Here’s the no-eyed, big-eyed wolf spider, lurking in a cave in Hawaii; the mysterious pink fairy armadillo from Argentina; the colossal Queen Alexandria birdwing butterfly from Papua New Guinea.

We travel from the coasts of the Comoro Islands, home to the “fossil fish”, the coelacanth, to the rockhopper penguins of Antarctica. One moment, we’re in a microlight above the Kalahari; the next with snow leopards in the Himalayas. As the catalogue of fast-disappearing animals continues, an intricate pattern of the fragile interdependence of species and habitats emerges.

Planet Zoo embraces the last wild places: the rainforests, oceans, African grasslands, Arctic and Antarctic and, closer to home, the Mediterranean (“a tale of over-fishing, pollution and ever-increasing human disturbance”) and what’s left of our own ancient forests and wetlands.

Each profile is beautifully illustrated by Alan Marks’s evocative watercolours: the addax, inthe shimmering desert sun; the monstrous turkey-like capercaillie in the Scottish highlands; a silhouetted leopard on its nocturnal hunt.

Barnes’s love of storytelling comes from his father, Edward Barnes, Blue Peter producer and later head of BBC children’s programmes, who also taught him not to talk down to children or dodge important topics. Brought up in south London, he had an early fascination with natural history and Saturdays were spent at the Natural History Museum in South Kensington (his “dinosaur period”). For his 10th birthday he was given a Golden Treasury of Natural History, “a book of unending wonders”, which he read repeatedly along with Lofting’s Dr Dolittle and Kipling’s The Jungle Book. But it wasn’t until after Bristol university and a degree in English literature, which took him into journalism, that he returned to his childhood passion.

Self-taught in biology, Barnes read Darwin, Lorenz, Stephen Jay Gould, Richard Dawkins and especially Edward O Wilson, the American naturalist who was the biggest influence on Planet Zoo. Wilson answers the question: Why bother? with his notion of biophilia or love of life. Anyone who’s ever patted a dog, stroked a cat, or fed ducks in the park, knows about biophilia, says Barnes. It’s part of being human and what links us to other living things on the planet.

Travel writing frequently takes him to Africa, in particular to the Luangwa Valley in Zambia, one of the great wildernesses of southern Africa, and the inspiration for much of Planet Zoo, as well as his first novel, Rogue Lion Safaris (Collins). In 1992 he took a two-month sabbatical in the Luangwa Valley - “the most beautiful place on Earth” - and sent a weekly bush telegraph to The Times, full of the sights and sounds of his riverside camp.

A year later he joined an expedition to the Zairean border with his friend, the ornithologist Robert Stjernstedt, to find Pearson’s Cisticola, a small brown bird last sighted in 1936.

Barnes now lives in Suffolk with his wife, Cindy, and six-year-old son, Joe, in a kind of wild-life paradise, not far from the Royal Society for the Protection of Bird’s famous wetland reserve at Minsmere. Their own nature reserve includes sheep, horses, cockerels, cats and dogs, guinea pig and two ferrets - one named Rikki after Kipling’s mongoose. He writes on sport, as well as wildlife, for The Times and has a regular column in the Royal Society for Protection of Birds’ Birds magazine.

During the winter he sees marsh harriers - once extinct in Britain - almost every day. They are one of the good news stories in Planet Zoo, along with the giant panda, the Eurasian otter, Arabian oryx and white rhino. Others, such as the ivory-billed woodpecker, reduced to a single breeding population in Cuba, may not be so lucky. How can we improve our success rate? “Believe in the importance of life on Earth and enjoy it,” says Barnes. “The fact is that all life is connected and when we harm one bit of the Earth, then we cause harm to all.” He urges young readers to get involved through organisations such as the World Wildlife Fund, RSPB, Birdlife International and the Wildlife Trusts.

Above all, he insists: “Don’t give up, don’t get depressed. Keep on hoping.”

‘Planet Zoo: 100 animals we can’t afford to lose’, illustrated by Alan Marks, is published by Orion Children’s Books pound;20