SEX AS SUICIDE

By MICHAEL D. LEMONICK

AS GENERATIONS OF BIOLOGY STUdents have learned to their morbid delight, insect-mating behavior can be pretty bizarre. The classic example is lovemaking among the praying mantises, where the female has sex with her partner, then eats him for dessert.

But the mantis has nothing on its distant cousin, the Australian redback spider. The spiders too have turned copulation into a girl-eats-boy story. In this case, though, the male not only lets himself be devoured; he also performs acrobatics to make it happen. As soon as the male has put what is delicately known as his intromittent organ into his much larger mate, he turns a somersault--without slipping out--and dangles his juicy abdomen right in front of her mouth. Who could resist? Not the female, who usually begins chomping away.

On the face of it, this seems insane. Since most redbacks do it, however, there has to be an explanation. Somehow, the male's odd behavior must have offered an evolutionary advantage, or it never would have become entrenched. Now Maydianne Andrade, a University of Toronto graduate student, reports in the current Science that she has discovered what it is. A female who is chewing on her boyfriend is distracted and allows him to copulate longer. That lets him deposit the maximum amount of sperm, giving him a better chance of passing along his genes. Beyond that, a sperm-filled female tends to spurn new suitors, ensuring that the suicidal male, not a rival, has the offspring.

This would still seem to be a dubious strategy, since the male necessarily mates only once. But male redbacks have a short life-span and rarely live long after copulation anyway. "It appears likely," says Andrade, "that one shot is all a redback male gets." By yielding to the female's consuming interest, he makes sure it is his best shot. --Michael D. Lemonick