Homing, and the evening roost

Many land snails spend the day in the same kind of place, and some spend it in the very same place: one crack, the underside of one pot, a marked spot on a wall. At dusk, or when rain wets the ground, they leave to feed. Before sun and wind dry the surface again, a surprising number find a way back.

How they do it is not one sense. Trail-following matters. A snail can taste a path it laid hours earlier and follow it, especially while the trail is damp. Chemical cues from the roost matter too, the smell of a familiar shelter and of other snails. Experiments with garden snails, and with slugs, have shown homing over a few metres, which is a long walk at their speed. Some studies have tested magnetic fields and skylight. The honest summary is that homing is real in several species, that chemical trails are the clearest mechanism, and that a snail is not navigating with a map of the garden.

The roost is about water. A day on open soil can kill a land snail by drying, not by hunger. The shell slows evaporation, the breathing pore can close, and a tight crevice of still, damp air does the rest. A cluster of snails on a wall is often a shared answer to the same piece of physics. They are not exactly a society. They are solving one problem in the same square metre.

A soft pencil dot on the old shell, never on the growing lip, is enough if you want to see whether one animal returns. Mark a few, not a crowd, and do not use paint, nail polish, or glue. The question is only whether this one came back to the same crevice in the morning. If it did, you have watched the trail do its second job.