BY CHRIS WINTERS
JUNE 26, 2016
EVERETT, Wash. — Whether you think snails are good looking or good for nothing (or good eating), one fact seems undeniable: The little critters are everywhere this year.
And they’re hungry.
“I have dahlias and several things that they just eat up,” said Barb O’Brien, secretary of the Everett Garden Club.
O’Brien, who also is a Snohomish County Master Gardener, raises hens, and she has sprinkled crushed eggshells around the plants in her backyard to keep the gastropods at bay.
“I think it is because they don’t like the sharp edges,” she said. “That seems to be working real well for me this year.”
The bane of many a Northwest garden, it’s hard to say definitively where the snails came from in such numbers, and even how many different kinds there are.
Origin of the species
Most of the land snails, and their shell-less cousins the slugs, aren’t native to the Pacific Northwest.
David George Gordon, the Seattle author of “The Secret World of Slugs and Snails: Life in the Slow Lane,” told one common origin story for foreign snails: a French immigrant wanting a little taste of the homeland.
“In the 1800s in San Jose, which back then was a farming community in California, there was a French vineyard owner who introduced escargot snails in California,” Gordon said. “He was like the Johnny Appleseed of snails.”
One species of escargot snail brought over was the grove snail (Cepaea nemoralis), one of the most common species in Europe, which is now widespread in the United States.
Gordon said he recently found a bunch of escargot snails in McCollum Park outside Everett.
Another problem species is the common or brown garden snail (Cornu aspersa), which originated in the Mediterranean but is now everywhere worldwide. The Port Townsend area has a particular problem, Gordon said.
Homegrown species, Gordon said, mostly are confined to the wilder parts of the region.
“Native species are living in forests where they grew up, they don’t really have use for a garden,” Gordon said.
The garden snail is a particular problem in California, where they infest citrus groves, said David Robinson, who for 21 years has worked for the U.S. Department of Agriculture as the national malacologist, the term for scientists who study mollusks.
“In California, it costs the state anywhere between $8 million to $10 million per year just to control and suppress it,” Robinson said.
The snails will eat anything, Robinson said. He also said it’s a myth that most invasive gastropod species are displacing natives.
“Most invasive species are those that we call synanthropic, which means they’re associated with human activities, human agriculture,” he said. “We’ve brought these species from elsewhere ourselves, and we have driven out the native species.”
Nurseries are major contributors to the spread of invasive snails. The eggs invisibly hitch a ride on plants brought in from out of the area and get planted in gardens and flower boxes everywhere.
But they also arrive on vegetables or on the exteriors of containers.
Robinson’s office is responsible for identifying any snail or slug that comes through an international port on or in millions of containers.
He used to do it all by himself, with samples sent by overnight express to his office at the Academy of Natural Sciences of Drexel University in Philadelphia. He’s since trained a number of mollusk observers at several key points of entry into the country, but it’s still hard to keep up.
“We are deluged,” he said.
Change in the weather
There’s another explanation for the sudden proliferation of snails, especially in recent years: changing weather patterns with more frequent dry spells.
“Snails can endure droughts better than slugs because they can pull back into their shells,” Gordon said.
The general warming of the climate, with milder winters, also means there are fewer mass killings during cold snaps.
Sharon Collman, an instructor at the Washington State University Extension in Horticulture and Integrated Pest Management, said snails seem to generally outnumber slugs now.
Collman said identifying newly introduced species is important for catching them before they multiply out of control.
A new species can lie in wait for 20 years, and suddenly people will see the population explode, she said.
“I’ve toyed with the idea of having a mini slug-fest to have people bring what they can find and see if we can pick up introduced species early,” she said.
The Pacific sideband (Monadenia fidelis) is a native snail and also the largest found in Washington, with shells up to an inch wide. It is one of many species known for shooting “love darts” into another snail during the mating process.
To the untrained eye, the native sideband and the invasive garden snail might be visually indistinguishable.
“Sometimes it can be a subtle difference,” Collman said, such as the width of the bands on the shells.
There could be 10 to 15 or more invasive species in western Washington, along with a similar number of slugs.
The exact number of different species is unknown because snails and slugs in the Northwest are not well studied.
“There’s really no one in this state studying snails,” said Clarissa Dirks, a molecular biologist at Evergreen State College.
Dirks said there’s a lack of real science being done, including identification, and genetic profiling, in peer-reviewed journals.
It’s hard even to tell some species of snail apart, Dirks said, because it requires catching and dissecting them to remove their teeth and scan them with electron microscopes.
Dirks recently studied snails at the University of Hawaii at Manoa.
“The reason I went and learned how to do all this stuff is it’s completely understudied in this state,” she said. “Until we have good genetics work, for example, we can’t easily identify them, so we won’t even know when we have new species around you.”