The common snails that chomp on backyard gardens and emerge after rains have wilder love lives than you ever dreamed.

To start with, the prelude to the mating process lasts for hours, as does the mating itself. Garden snails deliver sperm via a sharp barb, which they point rather aimlessly at their partner, to lodge in the head or anywhere else along the other snail’s body. They often miss, but not always.

Least remarkably, they are all hermaphrodites. Hermaphroditism, or having both biologically male and female sex organs, is a common trait among lots of animals. It’s the norm among animals like snails and slugs, and in their case, each animal can give or receive sperm at the same time.

But just because they can perform both roles with equal gusto doesn’t mean they do, explained biologists Ronald Chase and Kristin Vaga in a 2006 study on garden snail sex. Chase and Vega were skeptical that a hermaphroditic garden snail would be amenable to receiving an open wound on its own body and then bearing the burden of developing young afterward, since it could, in theory, pass along its own genes simply by darting another snail and then moving along.

“The concept of conflict is often the key to understanding mating behaviors and mating strategies,” they wrote. “The different interests of males and females fundamentally cause sexual conflict.”

One example of those different interests causing conflict can be found in hermaphroditic flatworms. The sparring between two individuals, each attempting to impregnate the other without receiving any sperm, is called “penis fencing.” Although both flatworms are equally capable of giving and receiving sperm, it’s a lot easier for each of them to impregnate the other and skedaddle than to grow offspring themselves. The result is often a marathon dance of “not it,” with members extended and at the ready the whole time.

Because the dart-shooting impregnation technique seems similarly aggressive, Chase and Vaga expected to find some indication of similar avoidance among the garden snails. They measured whether the snail that shot first had an advantage or whether snails made any effort to avoid being the first to receive the dart. They even collected data on how much sperm each snail delivered. But none of it made a difference: the snails seem truly content to let their partner perform an identical role, regardless of who got a faster start.

“Rather than having a conflict over the dart,” they wrote, “[t]he two courting snails seek independently to dart their partners and exchange sperm… The interactions between the snails appear to be entirely synergistic.”

In other words, they found no evidence that garden snails shy away from being pricked. The slimy creatures don’t mind splitting the responsibilities of parenthood (which are admittedly far less for a snail than a human) squarely down the middle—in more ways than one.



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Behavioral Ecology and Sociobiology, Vol. 59, No. 6 (Apr., 2006), pp. 732-739