The molluscan love scene in the film Microcosmos depicted snail sex as a squelchy, caring, sharing affair. Yet just before mating, many snails jab a mucus-coated calcium carbonate dart into their partners' flesh, leaving a nasty wound. This 'love dart', researchers now reveal, causes the target snail to retain more of the shooter's sperm 1 . Males do best by mating with as many females as possible.
Females go for quality rather than quantity.
In hermaphrodites, which include snails, these contradictory demands result in some rather odd behaviour. The hermaphroditic flatworm Pseudoceros bifurcus , for example, engages in 'penis fencing', attempting to give its partner a hypodermic sperm injection while avoiding being impaled and inseminated in the process. This is despite the fact that snails whose darts miss transfer more sperm, perhaps to make up for their poor marksmanship. The increased sperm storage seems to be due to a chemical in the mucus coating of the dart. An earlier study of dissected snails had shown that mucus causes the snail's female reproductive tract to contract, sealing off the entrance to the bursa copulatrix and diverting sperm towards the storage organs.