Camouflage in Snails

Lesser bulin (Merdigera obscura). [RN]
Merdigera obscura
Picture: Helmut Nisters.

The lesser bulin (Merdigera obscura) is the smaller relative of the mountain bulin (Ena montana).

From the North-East of Africa it is distributed over nearly all of Europe as far North as the South of Finland. The snail lives in deciduous forest on trees and under leaves, but also occurs outside of forests. Other than its larger relative it is not in need of humidity to an extent like its larger relative, the mountain bulin.

In 1838, however, this species received a rather unflattering scientific name, the genus Merdigera, literally meaning as much as "excrement bearer". Its species name, obscura, means "hidden" or "obscure".

The reason is, that the lesser bulin hides its shell under a camouflage of its own excrements and earth. If one finds a lesser bulin in nature, such as the specimen in the picture on the left in a wall crevice, it is hard to recognise, little connecting it to the clean shells known to us from shell collections.

With which degree of ingenuity snails can proceed in camouflaging their shell, the malacologist Christoph Allgaier has shown in the snail Napaeus barquini from the Canary island of Gomera.

To be able to also reach its shell tip, Napaeus barquini is able
to extend astonishingly far out of its shell aperture.
Picture: Christoph Allgaier.

This small snail species, another member of the bulin family (Enidae), is able to extend its body especially far outside of the shell aperture. This is of use, when the snail actively picks up pieces of lichen, which it also eats (and probably distributes by endozoochory), and places them on its shell. Even more, the snail, using its mouth, forms the lichen into spikes, thus optimising their camouflage - a quite astonishing evolution of behaviour.

  Allgaier, C. (2007): Active Camouflage with Lichens in a Terrestrial Snail, Napaeus (N.) barquini Alonso and Ibáñez, 2006 (Gastropoda, Pulmonata, Enidae). Zoological Science 2007, 24 (9), 869 - 876. (Link).

Camouflage is also present in numerous European snail groups other than Merdigera obscura: Among those the already previously mentioned bulins (Enidae), the corn snails (Chondrinidae), the leaf snails (Hygromiidae), the ton snails (Orculidae), the grass snails (Valloniidae) and the amber snails (Succineidae). Those often carry an additional layer of earth particles on their shell, which more probably get stuck there passively because of the snail's mucus. The hair, many of those snails (especially many Hygromiidae) bear on their shell surfaces, might also be of use.

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