Contact rehydration in the terrestrial slugLimax maximusL. in the field

Abstract

Specimens of Limax maximus were observed in the field between the hours of 10:00 p.m. and 2:00 a.m. as they entered a pool of rain water approximately 0.5 cm deep. Hemolymph was withdrawn from slugs before they entered the water and after they exited it. A significant proportion of the animals exhibited locomotion to the water source (i.e., orientation to water; 16/16) and retraction of the superior and inferior tentacles (13/16; χ2 = 6.25, p < 0.02), and there was a trend for animals in the water to flare the foot (11/16); these are all behaviors associated with contact rehydration. The mean hemolymph osmolalities of the two groups (i.e., 179 ± 29.6 (SD) mosmol∙kg H2O−1prior to entering the water versus 104 ± 29.8 mosmol∙kg H2O−1after exiting the water; n = 16) were significantly different from one another (t = 6.92, p < 0.001). Time spent in the water was inversely correlated with hemolymph osmolality (r2 = 0.715, p < 0.01). The calculated rate of change in hemolymph osmolality for the slugs was 3.7 mosmol∙kg H2O−1∙min−1. These data support the hypothesis that contact rehydration plays a role in regulating water balance in slugs in the wild.