Wolbachia is a fascinating critter. It’s a bacterial genus that infects lots of arthropods, and does all kinds of things to them that make great headlines, like killing males or making them eat brains. However, it’s commonness is disputed, particularly among insects that live in rivers and lakes (i.e. freshwater insects). So in this study, Eric Sazama answered the question, How many freshwater insect species are infected with Wolbachia? See the answer here, for free.