Minimalistic living and the tiny house movement reject spacious dwellings in favor of efficient homes. Typically, these petite houses can be small enough to be towed around in nomadic fashion. While it can be aesthetically and economically appealing, what is it like actually carrying an entire house with you everywhere?
Snails, and other members of the mollusk phylum, carefully balance the act of consuming resources and creating beautiful homes in the form of their logarithmically spiraled shells. One-upping the tiny-house movement, snails have truly designed transportable real-estate that is sustainable and optimized for their needs. To ensure survival, it’s imperative that snails consider their needs and environmental resources during the construction of their intricate shells.
The Greek oikos (“ecos”), meaning home or household, serves as the root for both ecology and economy which are both critical aspects of home building. To construct a house, the snail must consider the ecology, the study of the communication between living and non-living components of the ecosystem. Ecology takes a holistic approach to the science of dwelling considering all the interactions of organisms and their environment. Along with this, the snail must manage and spend the resources it obtains from nature economically. Careful organization of supplies allows it to move about the world, albeit at a snail’s pace, and produce its shell. The combination of ecology and economy accumulates into the artistic and portable home.
Like the modernist architectural movement cries “form follows function,” so does nature. This design principle states that the structure of a building or object should principally relate to its proposed purpose. Architect Louis Sullivan, famously states this aesthetic philosophy as such:
“It is the pervading law of all things organic and inorganic, of all things physical and metaphysical, of all things human and all things superhuman, of all true manifestations of the head, of the heart, of the soul, that the life is recognizable in its expression, that form ever follows function. This is the law.”
Which is just to say that the needs of a snail will dictate and shape the structure of its shell. So what is the shell’s purpose?
The word for mollusk (of which snails are classified) comes from the Greek word for “soft” as mollusks are squishy invertebrates. Protection by a hard mineral barrier is essential and achieved by shell formation in many mollusks. Exceptions are creatures like octopods and squids, but they have evolved other means of adapting and protecting themselves.
Some mollusks, especially of the bivalve class, further protect themselves by burying into sand. Named for their hard shell made up of two halves, clams, oysters, scallops, and other shelled-creatures found in your New England Chowder fall in this category. Different shell textures and patterns allow them to bury quicker (image below). For example, ridges on the shell provide grip to the mollusk to push through sand. The alternating pattern of steep dorsal and gentle ventral ridges allow for an alternating or sawing motion through the sediment. Some bivalves like razor clams can burrow through sand to a depth of two feet using their “aerodynamic” shell shape.
Just like in designed houses and urban planning, nature constructs abstract architectural beauty out of necessity. All homes are a form of protection and shelter because our homes are typically grounded to one spot they additionally need spaces to sleep and prepare food. Planning a house is more than designing rooms for functionality though and their construction requires material.
Snails, and gastropods in general, typically have a shell made of calcium carbonate: the same stuff that makes limestone and pearls. The combination of calcium, carbon, and oxygen atoms (CaCO3) is strong enough to serve as a sturdy structure for the snail to live.
Like human fingernails, snails are born with their shells though at this stage of life it’s called a protoconch (or “earliest shell”) and is very fragile. So the baby snail needs to devour a lot of calcium to help the shell harden, just like our bones need the mineral from our diet. Once ingested, the snail’s shell is formed, repaired, and maintained by the mantle (image below). This organ is able to secrete calcium carbonate which adds to the shell’s size and strength as the animal grows.
Because the building material of their shell is mainly composed of inorganic calcium, the shell is not made up of cells. This is distinct from some other shelled creatures, like turtles, where the turtle’s entire shell is more like a bone containing cells and nerves. As such, their shells grow with them while snails have to keep layering calcium in order for their shell to be the right size.
Each shell consists of several layers, the interior ones being more mineralized and the outermost layer coated with proteins. This roof-like protein layer, the periostracum, caps the rest of the shell and mantle and acts as a framework from which the outermost layer of calcium is suspended. Unlike the other layers, specialized cells seal a space between the mantle and the shell where calcium becomes highly saturated giving the shell it’s hardened surface.
Where many human houses opt for a study steel framed foundation, the innermost core of the snail shell, the nacre, has the smoothest and softest surface. This allows the body of the mollusk to move without mechanical hindrance of the inorganic hard shell. The nacreous layer, too, is composed of layers arranged in parallel sheets after starting from an irregular calcium carbonate deposition, and end up arranging into an ordered crystalline structure. As intermediate layers accumulate, the inorganic material further assembles atop the crystalline base until reaching the periostracum, that protein coated exterior. As the mollusk incrementally grows, there’s an environmental record of each layer – like the rings in a tree.
The iconic spiral that snails have are asymmetrically coiled with either a left or right directionality (clock- or counter clock-wise). This final morphology comes from biological parameters like body shape, the outline of the main opening of the shell, and how fast the shell is made along different points. Clockwise or counterclockwise twists typically classify the species – but sometimes mutations cause shells to have opposite directionality. Snails with the counterclockwise shell, the opposite directionality as typical snails, prevents their ability to mate as was the case with Jeremy the left-twisted snail until sympathetic humans found him a left-twisted partner, Tomeu. Luckily, the shape of our houses doesn’t prevent our ability to mate (though perhaps a sloppy interior may hurt one’s chances).
Spirals themselves are so common because the process of their physical maintenance is relatively easy – rotate a small angle, grow, rotate, grow a bit more, and so on. The final fractal-like coil, with multiple rounds of calcified layers, is also stronger. As the creature becomes bigger, the shell spirals to accommodate the changing size – not unlike additions to our houses.
Most of the time the coil is around a single axis, but in some species there can even be up to four coiling axes. Like contemporary architecture breaks from the traditional rectangular house, in this species of snail, the body has to detach and reattach, without reference support, to make a wild sinistroid pattern. Only shells have been discovered, such that neither live species nor their ancestors in fossil form have been found, so the how and why for these creatures remains a mystery. A more understandable, and practical, deviation from the snail-norm include the iconic conch with the high spire and siphon-like shape. These modifications help protect the “nose” area of the snail that locates food. Surprisingly perhaps, the beauty we find in intricate conches is not selected for evolutionarily in the snail themselves. The interesting and unique patterns and shapes are really just the most practical and useful for the snail’s survival.
All of this shell building necessitates the availability of resources and energy and their subsequent consumption. Taking a biological standpoint on the form-function relationship, an essential component is cost. Evolutionarily, certain designs and adaptations like a protective shell provide protection are advantageous. However, if the cost of its construction is too high, then the upfront price is too much for an organism to afford and the protection is unattainable. Here, the currency is the basics of life: food, shelter, and mating. All of these components play a role in terms of the cost of home maintenance as well.
The reduction in cost is important for the long-term economics of life. As with all evolution, costs vary by situation. Where some costs are worthwhile, others are not. Risks and rewards vary over time so the task of managing resources is a tricky one. Yet it’s incredible that inherently the snail will combine the surrounding inorganic matter of the environment to artistically produce something that wasn’t there before – a home and life.
Economically, it’s never been straightforward to own or maintain, let alone build, a house. Without a balanced budget, it can easily become overwhelming to try to allocate income and time to obtain basic needs. Where snails’ shells are optimized, perhaps the structures and buildings in which we live could reproduce their efficiency by having a more biological and ecological focus. It’s worth taking the time to reflect on our individual needs, determine how those play into larger ecological context, and respect the resources and space upon which our homes are constructed. Uniting form and function into one, our homes too could have practical simplistic beauty that lets nature into our homes rather than trying to keep it out.
References:
Natural History of Shells, Geerat J. Vermeij. Link.
Sullivan, Louis H. “The Tall Office Building Artistically Considered.” Lippincott’s Magazine (March 1896): 403-9. Link.