A Comparative Study of Aggregation in Pulmonate Slugs (Genus Limax)

Abstract

Limax flavus, L. pseudoflavus, L. maximus and L. marginatus are sympatric over parts of their habitat range in Ireland and therefore, probably compete for day-time resting sites. All 4 spp. home to an artificial shelter placed in their culture bins. Use of the home and closeness of aggregation in it may be described by the series L. pseudoflavus = L. flavus > L. maximus > L. marginatus, in which, L. pseudoflavus and L. flavus form closed packed huddles, L. maximus ceases movement on making contact with another slug and L. marginatus adopts a spaced distribution, in single species groups. Once within the home, L. maximus, L. pseudoflavus and L. flavus do not change their behavior in mixed species groups. The distribution of L. marginatus is disrupted by the close approach of members of other species. When mixed with L. pseudoflavus or L. flavus, significantly more L. marginatus and significantly fewer L. maximus occupy the home; L. flavus and L. pseudoflavus have nearest neighbors of the same species significantly more often than chance would nearest neighbors of the same species significantly more often than chance would indicate. L. maximus and and L. marginatus are not so segregated. Huddling apparently enables slugs to make greater use of daytime resting sites and to maintain their occupation even when sharing the site with more aggressive species.