ONE stick insect species may have been celibate for 1.5 million years.

Ditching sex means no risky matings, but harmful mutations build up over the generations, so asexual animals shouldn’t survive for long.

Bernard Crespi of Simon Fraser University in Burnaby, Canada, established the last time Timema tahoe stick insects had sex by studying mutation rates of two genes (Current Biology, DOI: 10.1016/j.cub.2011.05.026).

A lack of sex might eventually catch up with the insect, says David Hillis of the University of Texas at Austin, as 1.5 million years is not long in evolutionary terms. “It looks like asexuals arise commonly and must go extinct commonly too,” he says.