Snails can’t live in the California desert. Or can they?
Lizards in the desert? Yes. Scorpions in the desert? Of course. But snails? We are used to seeing snails in well-watered landscapes around our homes. But when I asked 12 people if they thought snails lived on the cactus-covered slopes that surround our valley, I received a unanimous “no.” Answers ranged from “it’s too hot” to “it’s too dry.”
Their conclusion was mine when I first moved to the Coachella Valley. I reasoned that snails required cool, moist surroundings. They lived in well-watered gardens, my 10-gallon aquarium and, based upon the shells I found on the beach, in the ocean. I was well aware that with their extremely porous skin, a Helix garden snail dehydrates within minutes when exposed to the summer sun.
So, I was surprised the first time I found snail shells in the desert. At the time I was a student in college. My roommate and I had become fascinated with the diversity and abundance of desert reptiles. Each spring, we would take weekly sojourns into the California deserts in search of them. We scoured canyons across California’s arid mountain ranges in hopes of discovering an illusive collared lizard, rosy boa or speckled rattlesnake.
But most of these creatures, most of the time, eluded us. We settled, instead, for other curiosities such as plants or animals that were rare or seemed out of place. In this latter category was my first encounter with snail carcasses, snail shells to be exact. They were easy to spot. Bleached by sunlight, the shells were bright white and contrasted dramatically with the dark gray sand and gravel on which they rested. Though no larger than a thumbnail, the spiral shells I found were sufficiently reminiscent of the common introduced garden snail (Helix) to make me confident it was a snail and not something else. This first discovery took place years ago in Berdoo Canyon just north of Indio. At the time, the access road into the canyon was not well known. Today, it is regularly used by many Coachella Valley four-wheel-drive owners as both the shortest and roughest road into Joshua Tree National Park.
Berdoo Canyon is a tough place to live for any animal. In its lower reaches, the temperature exceeds 100 degrees for more than three months every year. Rainfall averages less than 5 inches. It is a true hyperarid environment. My roommate and I couldn’t help but wonder how snails survived in such a clearly inhospitable place. Based upon the handful of shells we found on that day, however, I concluded land snails were not rare, at least not within Berdoo Canyon. Since that time, I have discovered land snail shells in nearly every desert canyon in which I have hiked; from Texas’ Big Bend National Park to our own Santa Rosa and San Jacinto Mountains National Monument. On rocky hillsides and in deep canyons it is hard to avoid them. Indeed, apparently native desert snails are not only surviving but thriving.
Desert snails are typically confined to microclimates in isolated mountain ranges. Their poor dispersal ability (they can’t fly like birds or run like mammals) and susceptibility to heat and dryness essentially trap them where they are. During the Pleistocene ice ages, however, cooler and wetter climates allowed snails to move, over many generations, between mountain ranges. During those times a few big populations existed which freely interbred — exchanging genes in the process. Their isolation today in widely scattered desert mountain ranges has resulted in the evolution of new species primarily through a process known as genetic drift. In this process, any organism changes over time as it carries a unique set of genes and adapts to a unique set of environmental conditions. Eventually, it changes so much it can no longer breed with snails from other isolated localities, even if a change in climate allows separate populations to reunite. The result has been the evolution of dozens, perhaps hundreds, of new species across the desert Southwest representing several genera. New species are discovered and described in the scientific literature several times a decade. Just a few years ago, biologist Lance Gilbertson discovered a new species in Mojave National Preserve, just a two-hour drive north of Palm Springs.
For more than a decade after I became aware of their existence, I had not encountered an actual living desert land snail. Bleached white shells were the rule. Occasionally, my hiking companions and I might stumble upon a recently deceased individual, identified in our area by the original color base of a tan, almost pinkish flesh tone. Inevitably, there is also a dark purplish stripe accenting the uncoiling shell. Such a shell is beautiful in its simplicity; particularly when compared with those of the familiar Helix garden snails.
My failure to find a living snail ended on a February afternoon while searching for evidence of bighorn sheep on the floor of Chino Canyon (the canyon in which the Palm Springs Aerial Tramway is located). A biologist friend and I were walking slowly up the canyon looking for sheep tracks and scat when I spotted something I thought I might never see, a living desert snail! It was crawling over a whitish rock that accentuated the nearly black flesh of the snail. The rock was wet from a light rain that was falling and, according to the thermometer attached to my backpack, the air temperature was a cool 57 degrees Fahrenheit.
From this first experience, as well as several later encounters, I concluded most Southwest snails survive in deserts not by enduring extremes of heat and aridity but by avoiding such conditions. For more than 95% of the year, a snail seeks shelter in a deep rock crevice. In such a miniature, cave-like environment, temperatures can approximate the average annual temperature which is less than 80 degrees in the Coachella Valley. Humidity is also much higher than on the desert surface. Based on field studies by Nick Waters of the Arizona Game and Fish Department, it seems the maximum temperature any desert snail voluntarily exposes itself to is 93 degrees Fahrenheit. That’s surprisingly warm but far from lethal for most desert animals. When hot and dry conditions prevail, the snail protects itself from water loss by crawling onto a flat rock and secreting an impervious cover across its shell opening. Ensconced, protected and stuck to a rock, it remains dormant until the next storm arrives in a week, month or, in some cases, a year or more.
When it does finally rain there is a flurry, by snail standards, of activity. Rehydration is first with snails being able to absorb water directly through their skin. Feeding is next. Though different species can be expected to eat different things, plant material, both living and dead, seems to be the choice. (There are carnivorous snails but apparently none of these are desert natives.) Eating moist and wet plants also helps in rehydration.
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Breeding is next and involves some novel adaptations. Most snails are hermaphroditic; they have both male and female reproductive structures and produce both egg and sperm cells. One snail finds another by following the mucous scent paths laid down as they crawl over the ground. Once a rendezvous occurs, they fertilize each other’s eggs. Since both snails in such a pairing lay eggs, their reproductive potential is doubled. Not a bad breeding adaptation where the odds of a hatchling snail surviving to adulthood are likely slim.
An even more bizarre breeding behavior is the darting of the mate. Not all desert snails have darts, but most do. The dart is a sharp, calcareous dagger explosively shot into the mate during copulation. Once a snail has darted its mate, it can fertilize the victim’s eggs. It is not clear if mutual darting occurs, but in either case the victim’s fertility is reduced, and lifespan shortened. A darted snail is much less likely to mate again ensuring its eggs are fertilized only by its first partner.
If you wish to view a desert snail alive, do what I did this past winter. Grab a flashlight and hike up a canyon on a cold night. (Most any desert canyon will do but the rockier the better.) Don’t start until it has been raining for one hour. Be patient. The rocks will be slippery and catclaw and other spine- or thorn-covered plants will scratch your skin. Of course, you’ll get soaking wet. Within two hours you have a good chance of finding a tiny, living snail in your flashlight beam.
The reward will be well worth the effort, depending, of course, upon how fond you are of snails.