A predatory snail distinguishes between conspecific and heterospecific snails and trails based on chemical cues in slime

Abstract

The rosy wolfsnail, Euglandina rosea, is a predatory snail native to the southeastern United States. It eats other snails and slugs, tracking them by following their mucus trails. Although wolfsnails follow mucus trails of both prey and conspecifics, they rarely eat conspecifics, and only conspecific trails are followed directionally. We investigated how wolfsnails distinguish conspecifics from prey snails (Helix aspersa) and how they determine directionality of conspecific mucus trails. We found that wolfsnails used chemical cues present in mucus to distinguish conspecifics from prey, and were less likely to attack a snail covered with wolfsnail mucus than one covered with prey mucus (experiment 1). Juvenile wolfsnails that were isolated from conspecifics before hatching recognized conspecifics as nonprey (experiment 2), and adult wolfsnails learned to follow trails of novel substances associated with exposure to other wolfsnails (experiment 3). Wolfsnails were equally attracted to both soluble and insoluble components of conspecific mucus (experiment 4) and followed conspecific mucus trails directionality even after the trails had been washed (experiment 5). We also examined whether a structural or chemical asymmetry in conspecific mucus allowed wolfsnails to determine directionality of conspecific trails. Although results of scanning electron microscopy provided no support for directionality using a structural asymmetry, manipulations of wolfsnail trails (experiments 6, 7) indicated that wolfsnails use a right/left chemical asymmetry in mucus trails to orient themselves on conspecific trails in the same direction as the trail-layer snail, independent of the trail layer's direction of movement.