One of the southern legs of the Oak Grove Loop Trail extends southeast from the picnic area (the northernmost southern leg, if that makes sense: at about 32.818693, -117.053897). There my wife, son, and I saw many hundreds or thousands of empty snail shells on the north side of the trail. On the southern side, there were almost none.
It looked like a snail apocalypse, except when we looked closer we could see that many were bleached white by the sun and weather, as if they’d been there for years, although a few still showed their stripes and coloring.
Why are there so many empty shells there? What happened to the snails? Were they drowned? Eaten? Poisoned? Killed off by disease?
I asked the folks at Mission Trails Regional Park and got an email response from Education Coordinator and Ranger Heidi Gutknecht:
Those shells are from the common garden snail, which has a large variety of natural predators, including ground beetles and parasites. If not killed and eaten by a predator, they are usually eaten by ants or just dry and shrivel up in their shell after dying. If you saw a whole bunch of empty shells in one area, it’s probably due to the recent rains washing them out from beneath the shrubs.
The brown garden snail, Helix aspersa, considered a pest, probably also accounted for a lot of the shells we saw. Some also could have been Rumina decollata, which eats brown garden snails, though I don’t recall seeing any of their distinctive elongated, conical shells.
Another snail predator has the fantastic name of the devil’s coach horse, Ocypus olens.
As you can see by Alan King’s photos of snails in the park, some snail shells look white even before sun-bleaching, so shells might have been more recent than they appeared.
But why so many snail shells?
Well, besides being prolific breeders (laying up to 80 eggs at a time — up to 2,000 over a lifetime, according to this 2001 Union-Tribune article), snail shells take years to disintegrate.
One academic study reports that the half-life of snail shells is about 7.5 years, meaning the shells will degrade by about half during that time. It would take another 7.5 years for half of the remaining shell to disintegrate, and so on. They lie in the underbrush until swept together by freshets and caught against natural barriers.
More information about snails and their natural predators, including pictures, can be found on a brochure and web page from the University of California Statewide Integrated Pest Management Program at UC Davis.
Correction: As pointed out in a comment below, the original description of a snail shell’s half-life was incorrect. It has been updated to accurately indicate how long a snail’s shell would take to decompose.
I’m Grant Barrett, engagement editor for voiceofsandiego.org. Drop me a line at grant@voiceofsandiego.org, call me at (619) 550-5666, and follow me on Twitter @grantbarrett.
Escaped Mystery Snails can die from drying out, or get injured when falling from the tank. So its very important to keep a tank covered to the extent possible.
“Salt essentially draws the water out of their skin – an osmosis effect – and they die within minutes of dehydration,” says Dr Gordon Port, senior lecturer at Newcastle University. “Slugs and snails are extremely dependent on a high water content in their bodies. They constantly need water to replenish any the lose.
Since mystery snails only live around a year or two at most, I figured it was caused by age. Eventually, through research, I realized that PH levels in the tank are the most common culprit for this problem.
Typically, snails are slaughtered by boiling. First, the animals are washed and soaked in water. Then, snails are put in boiling water and cooked to death (Thompson & Cheney.
Another way to tell whether your snail is dead or just sleeping is to examine his shell in front of a light source. If he's alive, you should see his heart beating. If you've just bought a snail, he may not move in his tank for the first two or three days.
Most species of land snail are annual, others are known to live 2 or 3 years, but some of the larger species may live over 10 years in the wild. For instance, 10-year old individuals of the Roman snail Helix pomatia are probably not uncommon in natural populations.
Its shell will drop and land on its side. Check to see if the body is dangling freely or if it is slipping out of the shell. If so, pick it up; if it doesn't move after that, it is dead. When a snail dies, its body usually goes back into its shell and starts to break down.
A snail's microscopic teeth are arranged in rows along what is essentially its tongue, called the radula, so its durable teeth are ideally positioned to scrape up, or rasp, food particles. Typically, its teeth are so small that this rasping is unlikely to break your skin and create a wound.
Snails have very simple brain cells, and these are not organized into a single brain structure like mammal brains. However, snails do react to their environments in ways that include moving away from certain stimuli, suggesting they can feel at least some form of discomfort.
Some studies have shown that mollusks like slugs and snails still can feel pain, so coating them in salt and dehydrating them isn't the most humane. If you've ever accidentally gotten salt in your eye, that could be a similar feeling to what slugs experience when you use salt.
Sometimes snails can also get "fungal infections." Fungal infections show up as white, fuzzy patches on the snail's body or shell. To treat this, you can use antifungal medicine made for snails. It will help get rid of the fungus and make your snail feel better.
Because mystery snail poop contains a high percentage of partially digested (plant) matter and an abundance of micro-organisms, they can actually be a valuable addition to your shrimp tank as an extra source of healthy shrimp food.
Garden land snails are so easy to take care of and make great pets. They're low-maintenance, enjoy being handled (see notes below on safety) and can be really interesting to observe!
Lifespan. Most species of land snail are annual, others are known to live 2 or 3 years, but some of the larger species may live over 10 years in the wild.
All snails need damp conditions to live in, or their soft bodies can dry out. Food: Freshly cut fruit and vegetables, such as cucumber, carrot, lettuce and sweet potato. Replace the food every two days or earlier if it is all eaten. The food can be placed in a small, flat dish or directly onto the substrate.
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