The “widow periwinkle” Littoraria melanostoma is a handsome little periwinkle living in mangroves along the coasts of East and Southeast Asia. Unlike many landsnails (which are usually hermaphrodite, that is, male and female at the same time), these estuarine snails come in separate males and females. Unhindered by any detailed knownledge of mollusks, one might assume that in sexual and other matters alike, snails are generally sluggish and docile. This is not generally the case, and also not in the widow periwinkle, as shown by Terence Ng and Gray Williams of the University of Hong-Kong in a paper just published in the Journal of Molluscan Studies.
Ng and Williams discovered that females, when they are mounted by a male, often use their snout to push the probing phallus away, time and time again, until the male gets so exhausted that he gives up:
In the video, the female is above, the male below; the female’s snout is seen pushing away the male’s phallus, which repeatedly appears out of the male shell beneath her.
The researchers tried to understand why a female would reject males so often (in about 90% of all mating attempts). They confronted large and small females with large and small males, but in all combinations the females were equally likely to push away a male’s penis, so it was not that the male’s weight and size was a reason to reject him. Also, they deprived females of sex for several months and yet found that after this long celibacy, the females still only accepted one out of ten suitors.
Long story short: the researchers still don’t understand why females give so many males the cold…ehm…snout. But one thing is clear: widow periwinkles are no pushovers.