Video of penis fencing in flatworms

For the first time, I got to witness penis fencing in flatworms before my own eyes!


What is penis fencing in flatworms?

Penis fencing is a mating behavior engaged in by certain species of flatworm. These flatworms are hermaphrodites, which means they possess both eggs and sperm-producing testes.During the fencing process, the flatworms "fence" by using their needle-like penises and gets into a violent fight to try and pierce their penis to anywhere in the body of the partner.

The "winner" of the penis fencing behavior is the flatworm which inseminates the other and it will be the father. The "loser" will be the mother which absorbed the sperm from the father and thus leading to fertilization.

Why is the mother the "loser"? It is because child-bearing requires considerate resources from the mother. Therefore, it is preferable to be the father than the mother from a biological point of view for these flatworms.

Below is the video of the process of penis fencing! Enjoy!

Penis fencing in flatworms from Loh Kok Sheng on Vimeo.