Schistosoma, or blood flukes, are probably one of my favorite parasitic worms. I read about them first in a book called Parasite Rex by science writer Carl Zimmer.
Blood flukes are so many shades of adorable that it’s ridiculous they are also remarkably long living. A blood fluke begins it’s life as a free-swimming larvae in a pond or stream. These flukes then seek out an intermediate host, a snail, and in this snail they feed and produce thousands of tiny flukes. These little flukes head back to the water in search of human skin. When they find their prize they drill inside making their way to the circulatory system and traveling to wither the small intestine or behind the bladder. Unlike most trematodes they grow up to be male or female and have to reproduce sexually. The female flukes are thin and long, the males are canoe shaped with a sucker on their head to assist in movement. When two flukes meet, the female will curl up into the grove of the male and they’ll stay like that indefinitely, the male feeding the female blood, and the female producing eggs which are evacuated from the host in feces or urine.
Blood fluke couples were known to be monogamous staying together for up to 40 years in some cases. They were also unique in that if 2 males blood flukes happened to find one another, they would also mate up, with one male curling up inside the other. Obviously no eggs are produced in this situation, which is good for the host as egg production is what can make a host sick. (If the eggs wind up in you liver it can cause schistisomiasis.) Blood fluke couple, whether 2 males or a male and female would very quickly regroup and rejoin if forcibly separated.
Adorable right? Unfortunately this fluke-ridden fairy tale has been spoiled by reports from researchers at Cambridge and the University of Perpignan. They found that if presented with a large variety of males, females will leave their partners in search of a more genetically dissimilar partner.
Even microscopic flatworms experience troubles of the heart apparently. Luckily for the fairytale joining of these lovesick flukes, a host is not usually infected with enough males suitors for infidelity to become an issue, and these happy couples can spoon and bleed their host together, until proper diagnosis and care do they part.