Q: Can you discuss the snails that seem to have become part of the landscape in the Philadelphia area? This spring they seem to outnumber slugs. Are they harmful? Slugs in disguise? Please tell us!! Thank you!
----Marjorie in Wissahickon
A. Well, Marge—the bottom line is that snails are essentially the same type of creature as the slimy slug, although I wouldn't call their shell a 'disguise'; it's more the result of a certain mineral being abundant or absent.
Both snails and slugs are mollusks—a huge category of invertebrates that also includes octopus and squid. Both move by means of a single muscular foot, leave trails of slime, have a body part called a 'mantle' on top of their back, are hermaphrodites and—at least the species that live on land—can consume lots of plant material. The shell that forms on the mantle of a snail is made of absorbed calcium—so you'll find fewer snails in areas with calcium-poor soils, and lots where calcium is abundant.
One of the main purposes of the snails' shell seems to be moisture conservation. Mollusks dry out easily, and a shell—especially one that the creature can fully retract into—is a good way to stay moist. But that shell is attached, meaning that slugs—even big ones—can slither into much smaller spaces to escape predators and/or stay moist. Slugs can even live underground, while snails have to stay on the surface, because of that big house on their back.
Some researchers theorize that snails actually came first, and slugs are an adaption that shed the cumbersome armor, rather than slugs slowly evolving the shell for protection. But I suspect that only snails would leave a large fossil record behind (in the form of their shells)—so who knows?
Anyway, it may seem that there are more snails in our listener's region because it's easier to catch a glimpse of snails during the day, when they essentially just need shade. Most gardeners don't actually see slugs unless they go out and inspect their plants late at night, when slugs are feeding. A lot of gardeners are overrun with slugs but don't know it because they only see the damage in the morning.
Q. I have pets and would like to know how to safely rid my garden of snails.
---Barbara in Huntington Beach, California
A. There are 12,000 species of land-dwelling slugs and snails, and one of the most destructive is the brown garden snail, which is the poster child for plant problems in many parts of California. This snail eats gardens to the ground, and is a major pest of orchards; a single tree can have thousands of snails up in its canopy.
That's right--they climb trees; orchardists will often wrap bands of copper around the trunks of their trees to keep the snails from climbing up, the same way raised bed gardeners use strips of copper around their raised bed frames to keep snails and slugs out. Slugs and snails won't cross copper barriers; the metal reacts with their mucus and gives them a kind of electric shock.
Another control method that's safe around pets is the use of beer traps; small containers baited with fresh beer and left out in the evening; the miserable mollusks can't resist the yeast and drown in the alcohol. Just to be sure to use fresh beer; despite 'common knowledge', slugs and snails like stale beer about as much as I do. And always refill your traps in the evening, so the beer will still be in good shape when the slimers come out.
Yeasty baits that contain iron phosphate—marketed under names like "Sluggo" and "Escar-Go!"—are also very effective; slugs and snails go for the yeast and then can't metabolize the iron. (These products are a great improvement over old school baits, which contained a highly toxic chemical pesticide.)
And in certain regions of Southern California you can buy "predatory snails"—a species that eats other snails, especially the brown garden snail.
And you can kind of eat the brown garden snail directly!
The brown garden snail is the one that's used in French cuisine; in fact, that's how this European native got to be California's biggest garden pest—it escaped from an operation raising them for the restaurant market. But culinary snails are bred under very specific conditions and fed special diets to get rid of toxins, and—at least theoretically—make them more edible. (Although many types of snails are eaten in many parts of the world, some species are poisonous and I wouldn't eat a strange snail any more than I would an unknown mushroom.)
But 'escargot export' could become another option if our besieged gardener is willing to provide the specialized conditions necessary to make her snails edible; there's a shortage in France, and some Californians are raising the garden pests for export!
Want more? Here's a great article on California snails.
And one on the snails of Pennsylvania.