The History of the World in Seven Snails

For National Snail Day, museum research fellow Melissa Betters explores the mollusks’ notable nature

Snails and their shell-less relatives, slugs, are gastropods within the animal phylum Mollusca. They are distantly related to other mollusks, including bivalves — like clams and mussels — and cephalopods — like octopuses and squids.

In honor of National Snail Day, Melissa Betters, a Peter Buck postdoctoral fellow at the National Museum of Natural History who studies deep-sea snails, looked at a few snail species to see what they can tell us about our planet’s history…and our own!

Life Finds a Way: Deep-Sea Vent Snails 

Early Earth was not a pleasant place to live. Riddled with volcanic activity and toxic gases, the earliest forms of life may have been tiny bacteria-like creatures that thrived in extreme heat and relied on chemosynthesis — a process that turns chemicals into food.

Thankfully, Earth has become much more hospitable over the eons. But there are still some places on the planet where infernal conditions mirror an early Earth. To thrive here, some hardy snail species have taken a page out of early life’s playbook.

These include deep-sea snails like Alviniconcha and Ifremeria which live at hydrothermal vents on the ocean floor, where super-hot, sulfuric water spews out of the seabed. Like the very first forms of life, these snails rely on chemosynthesis. They host chemosynthetic bacteria within their gills that convert vent fluids into food for both the bacteria and the gastropod.

The Cambrian Explosion: Fossil Marine Snail

For millions of years, life on Earth consisted primarily of small, simple organisms. But around 540 million years ago, life began rapidly evolving into new groups of complex organisms adapted to a wide range of habitats.

Popularly known as the “Cambrian Explosion,” this dramatic chapter in Earth’s history saw the appearance of nearly all the major animal groups alive today, including snails.

In 2020, scientists described one of the oldest known snail fossils, Pelagiella exigua, from the early Cambrian. Mineralized body structures like snail shells were an innovation during the Cambrian and helped provide structure and protection to these soft-bodied mollusks.

Colonization of Land: Fossil Land Snails

One of the greatest challenges that life on Earth had to overcome was the transition from water to land. Both plants and animals had to develop adaptations to deal with the pull of gravity, the risk of drying out and the UV stress from sunlight. Plants likely colonized land during the middle Ordovician Period around 470 million years ago, while animals are believed to have hauled themselves onto land roughly 100 million years later.

Snails were among the later arrivals. The oldest terrestrial snail fossils belong to the species Protocarychium mirum and Protocarychium arcidentata from the Late Carboniferous period between 350 and 300 million years ago. These fossils help researchers pinpoint when some snails ditched their gills and began breathing air.

Early Human Culture: The Abalone

When modern humans came onto the evolutionary scene around 300,000 years ago, snails had been crawling along for hundreds of millions of years. But it didn’t take long for these bipedal apes to begin incorporating the shelled mollusks into their budding cultures.

For more than 100,000 years, coastal communities have harvested abalone (genus Haliotis). These gastropods, which are found along rocky, temperate coastlines throughout the world, are an important source of food. Additionally, their shiny shells were perfect for tools, ornamentation and trade.

Abalone are particularly important to cultures living along the California coast. In the Channel Islands, archaeological evidence shows that Chumash communities began harvesting abalone over 12,000 years ago. Abalone also feature prominently in both Yurok and Wiyot mythologies from Northern California.

Early Trade: The Money Cowrie

When asked to picture “money,” most people think of paper bills, coins or simply numbers in a bank account. But in ancient times many would have thought of snails.

The aptly named Monetaria moneta — or the money cowrie — is generally accepted as being the world’s first international currency. As a result, it is potentially the most important snail in human history. This species is found in warm, shallow waters throughout the Indian and Pacific Oceans, but the most valuable and sought-after cowrie shells came from the remote islands of the Maldives. Much like how a Central Bank controls a nation’s production of currency, the remote range of the Maldivian cowrie gave its shells massive global value.

Durable, light, and difficult to counterfeit, money cowries were extensively used in trade throughout Eurasia and Africa. They circulated for longer than any other currency in history – from Neolithic China (3300-2000 BCE) to the trans-Atlantic slave trade. Even an old Chinese character for “money” (“bèi” (贝)) was derived from the depiction of a cowrie shell!

Social Class: Royal Purple Snails

The color purple has long been a symbol of royalty, but few know that we have snails to thank for that! Royal or “Tyrian” purple was a dye first produced during the Bronze Age (3300-1200 BCE) around the Mediterranean. Purple pigments were isolated from the mucus glands of three different marine snails (Hexaplex trunculus, Bolinus brandaris and Stamonita haemastoma) in a costly, laborious and highly secretive process.

It is estimated that 10,000 snails were needed to produce just one gram of purple pigment, making it one of the most expensive goods traded during the Roman Empire and costing up to three times its weight in gold. Its exorbitant price ensured that only the wealthiest members of society were able to (or, at times, allowed to) wear it. The beautiful, fade-resistant dye produced by these snails thus played an important role in the recognition of social hierarchies in early Western civilization.

Globalization: Giant African Land Snail

The spread of the giant African land snail is emblematic of a larger trend in biodiversity. As trade has globalized over the past 200 years, humans have introduced nonnative species across the globe, including several that cause ecological harm in their new homes. Invasive species have been implicated in 60% of known species extinctions worldwide.

Small but mighty, snails have been a rich part of Earth’s history for at least 500 million years. The next time you see a gastropod inching across your garden, remember how these easily overlooked creatures reflect the trajectory and history of our planet.