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Shell Of A Find: Scientists Reveal The World’s Tiniest Land Snails

One is smaller than a grain of sand, the other so small it decorates its shell with microscopic pieces of feces.

German and U.S. researchers have discovered two incredible snails, one of which is smaller than a grain of sand and believed to be the world’s tiniest land snail, and the second decorates its shell with tiny pieces of feces.

The presumed smallest species of land snail, which was found in Vietnamese cave sediments, has been named Angustopila psammion and is only 0.46 to 0.57 millimeters in size.

Adrienne Jochum from the Senckenberg Research Institute and Natural History Museum Frankfurt in Germany and the Natural History Museum of Bern and the University of Bern in Switzerland collaborated with scientists from the Netherlands, Hungary and the United States on the project that led the team to Quang Ninh province in northern Vietnam.

“It is truly special to discover such a record holder in the animal world, especially since this is, of course, not a matter of course, given the size,” Jochum said.

To retrieve the species from the sediments, the researchers had to wash the collected samples in a water tank. They allowed the foam on the water’s surface to dry, after which they recovered the tiny snail shells and other material. They then cleaned the shells with fine brushes and identified them under the microscope.

The smallest known land snail Angustopila psammion, 0.46 to 0.57 millimeters in size, was discovered by German researchers in Vietnam. (Senckenberg/Zenger)

“Our discovery immediately raised some evolutionary mechanism questions in terms of how some snails could be that small,” Jochum said. “The most plausible thing seems to be that the tiny snails can use previously unoccupied niches. Because of their size, they can search for food in confined spaces, as well as eat food particles, which are not interesting for larger animals.”

According to the scientist, their small size gives the snails the advantage of hiding from predators, which often consider them not appealing enough as food.

“We assume that the size of the snail we have found is already at the lower limit of adult land snails. The animals cannot get much smaller because there must be a certain number of neurons that make a snail functional. In addition, the snail shell must also offer enough space for at least one egg,” Jochum said.

The scientists’ method proved useful, as they found another unusual snail species in samples collected from Laos. The species known as the “dung collector” (Angustopila coprologos) is also very small, only 0.49 to 0.58 millimeters in size. It decorates its fine, porcelain-like shell with grains of feces, arranged in a radiating pattern similar to pearls on a necklace.

The “dung collector” snail, also known as Angustopila coprologos, is shown living up to its name. This unusual snail species was found in Laos. (Senckenberg/Zenger)

Other land snails often cover their shells with bark, lichen, clay or soil particles to avoid predators such as birds or beetles, Jochum said. “Such optical camouflage makes no sense for the extremely small snails that live in limestone crevices.”

Jochum suspects that the decorations might serve to attract mates or that they are used as “mini-sponges” that help the snail retain moisture and keep it from drying out.

“In any case, it is surprising that these tiny snails develop such complex mechanisms, about which we, so far, still know little,” Jochum said.

The research project was supported by the Hungarian Academy of Sciences and the Hungarian Research Fund, and the findings were published in the journal Contributions to Zoology.

Edited by Richard Pretorius and Kristen Butler

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