Courtship and the love dart

Land snails are hermaphrodites. A mature animal has both male and female anatomy, and in many species a pair exchanges sperm, so both partners can go on to lay eggs. That does not make mating simple, and it does not make it quick. Courtship in the garden snail Cornu aspersum can take hours of circling, touching with the tentacles, and pressing the feet together on a damp surface.

In Cornu aspersum and in other helicid snails, courtship can include a love dart. The dart is a small calcareous spike, grown in a sac inside the body, and one snail attempts to drive it into the partner’s side. It is not a packet of sperm. Sperm is exchanged separately, through the genital opening. The dart carries mucus from an associated gland, and that mucus changes the partner’s reproductive tract so that more of the shooter’s sperm is stored and less of it is digested. Snails break down a surprising share of the sperm they receive. The dart is a chemical argument against that digestion.

Not all snails use darts. Thousands of species court without one. The dart is a specialty of particular families, famous because it is visible and slightly shocking, and because early naturalists reached for Cupid when they named it. The metaphor is poor. The stab is a physiological trick, snails sometimes miss, and the partner is not charmed so much as chemically altered for the sperm transfer that follows.

After mating, sperm can be stored for weeks or longer, and egg-laying may wait for rain and for soil soft enough to dig. One mating does not imply one clutch, and one clutch does not imply one partner. The useful observation is plainer. Two snails joined on a wet wall at night are often courting, and they should be left to finish. Separating them to see the anatomy is how courtship gets recorded and also how it fails.