Ever wondered whether there was a real life equivalent of the Matryoshka Stacking Doll? In his brilliant book ‘I Contain Multitudes’, author Ed Yong describes the Citrus Mealybug. Like many animals, this little critter has incorporated bacteria inside its cells. What makes it so special is that another kind of bacteria lives inside that bacteria. A bacterium, in a bacterium, in a bug. So think of that next time you are eating.