Active disguise in land snails: Napaeus badiosus (Gastropoda, Pulmonata, Enidae) from the Canary Islands.

Some snails disguise the shell with a covering of soil or other material. Among species in the Canarian enid genus Napaeus, some rock-dwelling species cover the shell with lichens; in one of these, N. barquini, the process is known to be active. In some ground-dwelling species the muddy covering may be acquired passively, as for example in N. variatus. Napaeus badiosus is a snail with an almost smooth shell which is not disguised in the field. It normally rests out of sight of predators. Four specimens of N. badiosus were transferred to a glass terrarium with a layer of loose, humid soil without stones and vegetation. The snails acquired a soil layer with prominent protuberances that covered the whole shell, reducing the risk of attack by visual predators. The appearance of the disguised N. badiosus shell is compared with those of N. barquini and of N. variatus. The disguise of N. badiosus is similar to that of N. barquini. This active disguise thus appears to be facultative, adopted when hiding places are not available. Mechanisms of disguise are briefly discussed; the behaviour of other disguised species should be investigated.