Among snakes, sex appeal has benefitseven when it doesn't lead to mating. Findings reported today in the journal Nature suggest that male garter snakes emerging from hibernation impersonate females just so that other males will warm them up and conceal them from predators.

Previous explanations of female mimicry in various animal species have regarded it as an alternative mating strategy, in which impersonators may steal matings or avoid aggression from brawnier rival males. But when australian biologist Richard Shine of the University of Sydney and his colleagues examined the phenomenon in garter snakes, they could find no mating advantage to the she-males. Noting that she-maleness in these creatures occurs only during the first day or two after they emerge from their eight-month hibernationa period during which the snakes are cold and weakthe researchers propose another explanation for female mimicry. Perhaps, they offer, this strategy evolved as a way to get warm and evade predators, such as crows.

Field observations show that when an alluring she-male snake exits its hibernation den, male suitors form a so-called mating ball around it almost immediately. Perhaps not surprisingly, this mass of amorous males provides a great deal of warmth and protection to the object of their affections. Moreover, subsequent laboratory experiments demonstrated that such warming does, in fact, speed the vulnerable snake's recovery from hibernation: she-males that were kept warm regained their fully male status within three hours, while those kept cool retained their she-maleness for more than five hours. Thus "although intuition would favour an interpretation that female mimicry has evolved within the context of alternative mating tactics," the authors write, "simpler explanations should also be investigated."