How Do Snails Get Their Shells? And More Questions From Our Readers

Mollusk illo
All mollusks build their own shells. Illustration by Lisa Ballard

Q: How do snails get their shells? 

—Peter Ramirez | Gladstone, Oregon

All mollusks build their own shells, whether they live in water or on land. Creatures like snails, clams, oysters and mussels use an organ called a mantle to secrete layers of calcium carbonate, which crystallize and harden. Mollusks have a physical bias toward the right, just as most humans are right-handed, and this makes their shells spiral clockwise. (Very rare mutations can produce “left-handed” mollusks, whose shells spiral counterclockwise.) These coiled shells are compact and have a low center of gravity, making them efficient to carry as they protect their soft-bodied inhabitants from predators (and in the case of ocean mollusks, from tides and waves). Mollusks stay in the same shells for their entire lives and never stop adding to them, though they add less and less as they age. “It’s like each shell is a snail’s autobiography,” says Jerry Harasewych, curator emeritus at the National Museum of Natural History. 

Q: How does wildfire smoke affect the movement and communication of bees? 

—Valerie Townsley | French Gulch, California

Bees use the sun to orient themselves and communicate their locations to others. When the sunlight gets polarized by smoke, bees become disoriented. The threat is even worse for domesticated honey bees, who live in aboveground hives and can’t hunker underground the way wild bees can. They’re also loyal subjects. “Honey bees will not relocate if fire approaches because the queen is typically incapable of flight at that stage of hive development,” says Floyd Shockley, an entomologist at the Natural History Museum. “And they will not abandon their queen.” If the wooden frame of their beehive catches fire, the bees will be consumed along with it.

Q: What is the earliest record of humans thinking about an afterlife? 

—Hannah Long | Saltillo, Mississippi

Written records are full of beliefs about the afterlife, from reincarnation to resurrection, but they date back only about 5,000 years at most. There’s no way of knowing prehistoric people’s thoughts. “Beliefs do not fossilize,” says Rick Potts, a paleoanthropologist who directs the Smithsonian’s Human Origins Program. Starting between 100,000 and 130,000 years ago, Homo sapiens living in what is now Israel buried people with items like animal bones, seashells and ocher pigment, perhaps because they thought the deceased could use those items in the next world. But these relics might simply show that early humans honored and grieved their loved ones—something other primates like chimpanzees have also been shown to do.

Q: What is the rarest item in the Smithsonian collection, and how was it obtained?

—Linda Lee Ahn | Lake Ariel, Pennsylvania

It’s impossible to single out the rarest treasure in a collection of 155 million items, says Richard Kurin, the Smithsonian Distinguished Scholar and Ambassador-at-Large. But many objects have incredible acquisition stories. For instance, when the first gold nugget was found in California in early 1848, members of the U.S. Army brought it back to Washington, D.C. for testing. In December 1848, President James K. Polk formally announced the discovery, launching the gold rush. The Smithsonian inherited the nugget in 1861. “The lesson is, small item, huge consequences,” Kurin says. 

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