The shells of some land snail species carry an additional camouflage layer consisting of soil. Up to now the origin of the camouflage layers of snails has remained unexplored.
When examining a bizarrely camouflaged snail species named Napaeus barquini, biologist Christoph Allgaier at the Eberhard Karls Universität Tübingen, Germany, made some surprising discoveries.
This snail from the Canary island of La Gomera produces its impressive camouflage layer by itself in the process of an unexpectedly complex behavioural pattern. The snail grazes lichen material from the substrate and applies it to the surface of its shell with its mouth. Even young snails are able to do so.
As a result, a snail carries mountains of bizarre protuberances on its shell. The modelizing of the building material by the aid of its mouth is so far a unique behaviour among molluscs.
The studied snail species occurs on rock faces covered with crustose lichens. In a unique manner the snail forms the applicated material into long protuberances using its mouth. As a result, the thickness of the camouflage layer may exceed the shell thickness up to 100 times.
The snail is able to deposit lichen material even in the farthest regions of its shell by extending its body amazingly far beyond the shell margin. Due to this camouflage layer the outlines of the shell merge optically with the surface of the rock faces, presumably an adaptation to natural enemies such as birds and lizards.
By Allgaier's investigation it was given clear evidence in a camouflaged land snail that the extraneous layer is positioned on the shell by the animal itself. In contrast to previous hypotheses it is an active process. In addition, the investigated species carries a so far not described sculptured layer with protuberances, which is not known from any other camouflaged snail species. In the known cases, camouflaged snails carry only uniform extraneous layers on the shells.
Some weeks ago, Christoph Allgaier won the first prize for the best oral student presentation at the World Congress of Malacology in Antwerp, Belgium. The title of his communication was "Active Camouflage in a Snail".
These results were now published in the scientific journal Zoological Science (24: 869-876 (2007) doi: 10.2108/zsj.24.869).
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