Environmental orientation by terrestrial Mollusca with particular reference to homing behaviour

The homing of nine species of slugs and snails was studied in field and laboratory cages. All species were able to relocate artificial shelters from > 1 m distant. When it was rainy or windy, molluscs approached shelters in a spiralling manner, but in calmer, drier weather approaches were direct. Navigational behaviour to shelters was similar among all species.An experiment with Ariolimax columbianus showed that these slugs returned to the same shelters over long periods but moved more frequently if nearby shelters were occupied by conspecifics. Unoccupied shelters were "discovered" more slowly.A seasonal trend in shelter abandonment was associated with increased movements among shelters by several species. This trend was significantly correlated with shelter temperature.In the laboratory molluscs homed several times each night, apparently by following air-borne odor gradients in still air. Following slime trails was common, and was sometimes involved in homing. However, it also serves other purposes (territorial defense, locating mates, reducing locomotor costs).In one experiment Arion ater preferentially homed to shelters containing carrot-derived faeces as opposed to those containing only carrots. A homing pheromone was suggested, contained either in their faeces or in the mollusc's slime.