The fine art of hunting microsnails

Beauty and sorrow in five millimeters or less


TEENY TINY Some of the most elaborately spiked and contorted terrestrial snail shells, as on this Plectostoma concinnum, are among the smallest, 5 millimeters or less.

Peter Koomen

There’s a trick to finding new species of miniature snails: a bucket of water.

“Microsnail” is the term for the creatures with shells measuring 5 millimeters or less, sometimes much less. A species described from China, photographed perched in the eye of a needle, ranked as the world’s smallest known land snail for five days in the fall of 2015. Then the journal ZooKeys described an even smaller species, from Borneo.

“The very tiny ones you wouldn’t see even if you put your nose on the ground,” says Menno Schilthuizen, who described the Borneo miniature with colleagues. To avoid dirty noses, the researchers drop soil and leaf litter into a bucket of water, and shells float to the top. The shells are empty, alas, but “you can easily find thousands in just a few liters of soil,” he says.

Even scooping bucket flotsam has its complications. Schilthuizen, of the Naturalis Biodiversity Center and Leiden University in the Netherlands, has been studying the snails of Borneo’s limestone hills and caves since 1997. “Sometimes people bury their dead in a cave,” he says. So they’re reluctant for anyone to enter, even for snail science. Bird nest collecting gets in the way as well. Families harvest cave swiftlet nests, a sought-after ingredient in exorbitantly priced bird’s nest soup. “These nests are very valuable and there’s a lot of poaching going on,” he says. Disputes are often settled with “a lot of shooting with homemade guns.”

Borneo’s limestone, shown here in the pinnacles of Mount Api, offers habitat for snails because of its abundance of calcium for shell construction.© Gabbro/Alamy Stock Photo

Of the 48 new species of snails from Borneo that Schilthuizen and colleagues named in November, the world’s smallest “was the most boring in terms of shell shape,” he says. In contrast, the region’s Plectostoma microsnails curl in fat whorls, like tubing that vents a clothes dryer. Some loop back on themselves or flare out like a tuba. “Sometimes, they tie themselves in knots,” he says. Perhaps the contortions make it more difficult for a predator to get a good grip.

Snails typically have small, or even micro, habitat ranges. At some of Borneo’s isolated limestone peaks, “you can actually stand in front of the hill and see the whole world population of one particular snail species,” he says. The sad part of microsnail hunting, Schilthuizen says, is discovering that a company blasting a hill to extract the limestone has wiped out the entire world population. RIP, Plectostoma sciaphilum.

Susan Milius

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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