Penis Fencing

To borrow from the great comedic folk duo, Flight of the Chonchords “Yeah, you sexy hermaphrodite lady-man-lady, with your sexy lady bits, and your sexy man bits too, even you must be into you-oo-oo.” Hermaphroditism is common in marine invertebrates and the, flatworms are no exception.  Certain species of flatworm engage in a behavior called penis fencing.  Both swordsmen in this sexual fight are equipped with two-headed dagger-like penises.  The champion is the individual that inseminates the other by jabbing them.  The sperm is absorbed through the skin, and makes its way to the ovaries. The loser is fertilized and stuck with a bunch of crying little flatworms demanding energy and time.

Losers and winners are not always the case in hermamphrodites.  Often both are winners in which a mutual exhange of sperm occurs.

Dr. M (1729 Posts)

Craig McClain is the Assistant Director of Science for the National Evolutionary Synthesis Center, a National Science Foundation supported initiative. He has conducted deep-sea research for 20 years and published over 50 papers in the area. He has participated in and led dozens of oceanographic expeditions taken him to the Antarctic and the most remote regions of the Pacific and Atlantic. Craig’s research focuses on how energy drives the biology of marine invertebrates from individuals to ecosystems, specifically, seeking to uncover how organisms are adapted to different levels of carbon availability, i.e. food, and how this determines the kinds and number of species in different parts of the oceans. Craig’s research has been featured on National Public Radio, Discovery Channel, Fox News, National Geographic and ABC News. In addition to his scientific research, Craig also advocates the need for scientists to connect with the public and is the founder and chief editor of the acclaimed Deep-Sea News (, a popular ocean-themed blog that has won numerous awards. His writing has been featured in Cosmos, Science Illustrated, American Scientist, Wired, Mental Floss, and the Open Lab: The Best Science Writing on the Web. His forthcoming book, Science of the South (, connects cultural icons of South such as pecan pie with the science behind them.

3 comments on “Penis Fencing
  1. Is there really a ‘loser’ or a ‘winner’? Or is this all just our perception of the interaction between two animals? I posted about this very clip earlier in the week and have provided a re-sound-tracked version of the penis fencing footage. I think it tells a different story, and suggests a different narrative.

  2. Pingback: In Penis Fencing Everyone Wins | Nakedcircus

  3. jebyrnes thanks so much for your redone video, with that music it really gives it a whole different look the whole mating fencing thing. Thanks to you both for such and interesting blog and site.

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