Some male garter snakes, two University of Texas zoologists have found, impersonate females so as to distract amorous male rivals and, probably, gain better access to females.

Female impersonation, or female mimicry as zoologists prefer to call it, is known in other species, mainly fish. Now, however, it has been found among reptiles.

Garter snakes mate when a female produces an attractive scent, a pheromone, that exudes from her skin. Males detect the scent by smelling with their tongues, which flick out to pick up the aromatic molecules.

A single female typically draws anywhere from 10 to 100 males into a writhing tangle of snakes, each male trying to court the female by rubbing his chin along the female's back. No matter how big the mating ball, as it is called, only one male succeeds in mating.

When Robert T. Mason and David Crews, of Texas' Austin campus, examined mating balls, they discovered that 14 percent of them contained no female at all. Instead, they found one male that was producing the female's pheromone, and all the other males were courting him. They dubbed the attractive males "she-males."

In field observations, the scientists found that she-males that joined established mating balls distracted many of the ordinary males. They speculate that this gives the she-males a better chance of mating with the real females.