Worms have a number of sexual tricks. In addition to exhibiting a range of hermaphroditic abilities they can also undergo a complete sex reversal. Thus in one type of Syllis the female will change into a male once it has laid its eggs, and will then seek out a group of females to mate with. Females can be artificially converted into males by the simple expedient of cutting off half of the posterior ring of their bodies. (The ancient question that troubled the Greeks as to whether males or females enjoyed sex most could presumably be answered by worm individuals that have tried it both ways!) The oyster (Ostea edulis) also has the habit of changing sex, but with a frequency dependent upon temperature. In one study at 20-22°C., an individual became female once a year, where as at 14-16°C., once every three to four years!