An outbreak in recent years of deformities in frog legs may be caused by a simple parasite found in nature rather than by chemical pollution, according to two new studies published today in the journal Science. The new research, conducted on Pacific tree frogs in California, suggests that limb deformities are caused by a tiny parasitic worm that bores into tadpoles and disturbs the cells responsible for leg growth. “This is very good news, because the alternative is just a catastrophe,” said Stanley Sessions, chief author of one study. Still, the researchers emphasized that their findings did not rule out the possibility that chemical pollutants or increasing ultraviolet light caused by a thinning ozone layer could be contributing to deformities in other locations.