Slug Sex


Banana slugs, which are hermaphrodites, have some unorthodox mating rituals, to say the least:

[Zoology professor Harold Heath] caught a couple of slugs in the act. He noted the biting and the insertion. And then Heath observed something puzzling. As the slugs were withdrawing their penises, "one of the animals turned its head and commenced to gnaw upon the walls of the organ," Heath wrote. The biting was "unusually vigorous," he added, "and within a very few minutes the penis was entirely severed."

Scientists call this apophallation, and it may confer an evolutionary advantage over rival slugs:

Imagine you have two slugs, Taylor and Bailey. They mate, and then Taylor chews Bailey’s penis off. Bailey can still receive sperm. However, because Bailey doesn’t have a penis, he can’t fertilize anyone else’s eggs. So maybe he won’t seek out more mates. Or perhaps he seeks them, but can’t find anyone willing to mate with a penisless slug. Either way, that works out well for Taylor. Chewing off Bailey’s penis helped ensure that Taylor’s sperm will fertilize Bailey’s eggs, thus Taylor gains the upper hand. Miller’s research supports this idea, but it falls short of conclusive proof.

Of course, the decision to chew another slug’s penis off isn’t as clearcut as it might seem. When one slug begins chomping, the other typically responds in kind. And then they both lose in this evolutionary penis-chewing arms race.

(Image via Wiki Commons)