In the cottony cushion scale—a common agricultural pest that grows to about a fifth of an inch (half a centimeter) long—a new phenomenon has arisen: When some females develop in fertilized eggs, excess sperm grows into tissue within the daughters.

This parasitic tissue, genetically identical to the female's father, lives inside the female and fertilizes her eggs internally—rendering the female a hermaphrodite and making her father both the grandfather and father of her offspring, genetically speaking.

Though this new form of reproduction hasn't replaced cottony cushion scale sex, "this parasitic male has taken off like an epidemic in population," said study leader Andy Gardner, an evolutionary theorist at the University of Oxford.

"Once [this trend] gets started, it's going to sweep through