They're fighting ever more fiercely for the chance to advise us on our sex lives. Dr. Laura, Dr. Ruth, Dr. Phil, Dr. Oprah, sensitive Dr. Masoch and hard-liner Dr. Sade (not to mention the tireless Dr. Spam) -- they seem to be everywhere in recent months.

They're on television, the radio, the covers of women's and men's magazines. Surely the need for sexual advice and the desire to learn what sexual advice others require are not endless? Who will be left when the market shakes out? I believe it may turn out to be the sexual advisor who combines two popular genres into one blockbuster feature. Hint: Animal Planet.

In the chatty, opinionated guise of Dr. Tatiana, Olivia Judson brilliantly combines the ever-popular genre of the advice column with that of Sick Nature Facts. The combination is strikingly successful. As Dear Abby never has, Dr. Tatiana confronts the etiquette issues involved in depraved cannibal incest, for example, and uses them to illuminate biological insights into the nature of life on earth.

A typical section of Judson's book, Dr. Tatiana's Sex Advice to All Creation will begin with a letter from a troubled or inquiring life-form and will go on to explore issues raised by that creature's situation. She examines an instructive variety of dilemmas. I am particularly fond of a letter from "Hoodwinked in the Gulf of California," one of life's winners who nevertheless feels as if he's slowly going mad: "I'm a sponge louse, and I recently won a battle for a sponge cavity that is home to a large harem of beautiful girls. But I'm starting to suspect that some of the girls are not what they seem: several look like men dressed as women. Am I being paranoid?"

Then there's "Anxious in Amboseli," an elephant with whom many will identify, who concludes his plaint: "I'm obsessed with sex. Night after night I have erotic dreams, and the sight of a beautiful cow sends me into a frenzy. Worst of all, my penis has turned green. Am I ill?"

Dr. Tatiana is able to reassure Anxious that his situation is perfectly normal, which is in fact her response to many worried beings. Her explanations of various bizarre evolutionary successes are clear and compact. My only complaint would be that I want to read even more letters from correspondents like "Neglected Househusband in Tamil Nadu" (a bronze-winged jacana) or "Group Sexists in Santa Catalina" (sea hares).

Dr. Tatiana often takes quite a folksy tone. (Surely this is fair to say when she addresses readers as "folks"!) Although I have read vast numbers of books on biology for popular audiences, I believe this is the first time I have encountered the term "rumpy-pumpy." (In reference to the love life of Australian seaweed flies, as you might have guessed.)

Many are the shocking and tangled relationships revealed in Dr. Tatiana's answers to her pen pals. No doubt you knew about and had adjusted to the hermaphroditism of banana slugs, but perhaps you were not aware that during sex the "gigantic and complex" penis of a slug may get stuck, whereupon one or the other of them has to gnaw it off. This ends that slug's chances of playing the male role, but happily it remains in touch with its feminine side.

Then there are the button beetles (Coccotrypes dactyliperda), of whom you read so little in the newspaper. Who has not heard the scuttlebutt to the effect that button beetles can and often do mate with their own brothers or sisters when they've only just hatched?

Dr. Tatiana describes the even more scandalous behavior of a female button beetle who goes out in the world without taking this precaution. "On arriving at a new home, (she) . . . digs out a grotto and then lays a small clutch of unfertilized eggs. These develop into males. She mates with the first to hatch and then eats him and his brothers before laying a large brood of daughters -- and perhaps one or two more sons for her girls to mate with." Worse still, these amoral creatures are known to infest buttons on clothing.

Judson closes the book with a transcript from "Under the Microscope: The Deviant Lifestyle Show!" with host Dr. Tatiana (glamorous in a scarlet suit) interviewing Miss Philodina roseola, the bdelloid rotifer, about whether it is true that bdelloid rotifers have reproduced only by cloning -- no sex -- for the last 85 million years.

In a postscript, Dr. Tatiana notes that the more she learns about the sexual practices and predilections of others, the more tolerant and, in some cases, the more envious she becomes.

"I now think that many more things are normal," she says, and wishes everyone "lots of great sex" unless they happen to be bdelloid rotifers.