The life of the cottony cushion scale insect reads like something from the most ridiculous of tabloid newspapers. Dad leaves parasitic body parts in his own daughter, which produce sperm that fertilise her eggs. He is both father and grandfather to his own grandchildren.

On top of that, these insects are mostly hermaphrodites. With the exception of the odd pure male, almost every individual is both male and female. They reproduce by having sex with themselves, fertilising their own eggs with their own sperm. And this means that scale insects can be father, mother, grandfather and grandmother to all of their grandchildren. Good luck drawing that family tree.

Scale insects are small animals that suck on plant sap for a living. Encased in bizarre waxy shells, most people wouldn’t even recognise them as insects – the cottony cushion scale, for example, looks like a dollop of shaving foam. It and two of its close relatives are the only known hermaphrodites out of several millions of insect species.

In most hermaphroditic animals, an individual grows up and develops the organs that make both sperm and eggs. But that’s not the case for ...