Remember that couple you knew, the ones who went out on a date and instantly fell in love, who had been together for years and seemed as happy together as the day they met, the ones who gave you hope that you might find your own true love, the ones who made you feel that there was joy to be found in the world? And remember how one day they suddenly called the whole thing off and pretty soon were seeing other people, leaving you confused and reeling?

I’ve been having the same experience with blood flukes.

I first encountered blood flukes while doing research for my book Parasite Rex. They are extraordinary flatworms that get their start in life