A humble species of fruit fly is the genetic equivalent of a Russian doll – peer inside its DNA and you will see the entire genome of a species of bacteria hidden within.

The bacteria in question is Wolbachia, the most successful parasite on earth and infects about 20% of the world’s species of insects. It’s a poster child for selfishness. To further its own dynasty, it has evolved a series of remarkable techniques for ensuring that it gets passed on from host to host. Sometimes it gives infected individuals the ability to reproduce asexually; at other times, it does away with an entire gender.

Now, Julie Dunning-Hotopp from the J. Craig Venter Institute and Michael Clark