Bdelloid rotifiers are microscopic animals that live in birdbaths, rivers and on mosses. They’ve been around for at least 40 million years. Which is particularly amazing, because they’ve never had sex. No, they didn’t all take a vow of celibacy. It turns out the rotifers are all female. They multiply by parthenogenesis—from unfertilized eggs. That feat is not that unusual in nature. But the fact that the little critters have evolved into quite distinct species is. Scientists at Imperial College in London used DNA analysis and a scanning electron microscope to find that the rotifers have adapted to minute differences in environment, even though they reproduce from only one parent. For example, two species of rotifer that live around different parts of the water louse have different jaw shapes and body sizes. That’s important because it was long thought that sexual reproduction was necessary for such diversity to evolve, and for a species to thrive. But with 40 million years under their chastity belts, and counting, the rotifers seem to have found the road to success without sex.