The slowest invasion: Non-native snails take over the Northwest | (2022)

EVERETT — 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’s sprinkled crushed eggshells around the plants in her back yard 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 snails are feasting on her hostas, and she recently discovered them in her boxwood shrubs.

“I didn’t even realize they ate boxwood,” O’Brien said.

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.

Million dollar problems

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The garden snail is a particular problem in California, where they infest citrus groves, said David G. 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 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 if you want to catch 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 is 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.

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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 the Evergreen State College.

Dirks said there’s a lack of real science being done, including identification, genetic profiling and publication 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 under some of the top researchers in the field of malacology at the University of Hawai’i 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.”

The most up-to-date guides to snails and slugs that would apply to the Pacific Northwest are Canadian, Robinson said.

That includes Robert G. Forsyth’s “Land Snails of British Columbia,” which covers a biome similar to Washington’s, and the Canadian government’s free publication, “Identifying Land Snails and Slugs in Canada.”

Aside from an occasional publication by a museum or university researcher identifying a new species, the last comprehensive U.S.-based publication was the 2,107-page, two-volume monograph by Henry A. Pilsbry, “Land Mollusca of North America (North of Mexico),” published in four installments from 1939-1948.

“Since then, there’s been very little published, which is why I’m working on a paper right now to list all the known invasive snails and slugs in the U.S.,” Robinson said. “It’s looking more like a book than a paper,” he added.

It’s fertile territory for exploration, and Dirks has conducted some small surveys with her students in and around Olympia. Her field work has turned up examples of what may be previously unknown species.

“There’s an orange slug out there that I’ve looked around for, that I haven’t seen anywhere else,” she said.

Emerging problems

Snails and slugs bring more problems than just chomping on your garden vegetables.

Non-native leopard slugs (Limax maximus), in particular, are quite aggressive, Gordon said.

“A lot of slug species will — if you imagine this in slow motion — chase down native species and bite them and try to kill them,” Gordon said.

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Their victims include the two most common slugs native to the Pacific Northwest: the Pacific banana slug (Ariolimax columbianus) and the self-amputating taildropper slug (Prophysaon andersoni).

The robust lancetooth (Haplotrema vancouverense) snail is also destructive: Its tongue has raspy teeth on it. “They use them to pull other snails out of their shells and eat them,” Gordon said.

The threat of invasives is acute in Hawaii, which has a large and isolated population of gastropods that researchers want to protect from outsiders.

For example, Hawaii imports most of its Christmas trees from Washington, Dirks said.

“There were years when they had to reject huge loads of trees because they were covered in slugs and snails,” she said.

Another species of concern is the vineyard snail (Cernuella virgata). It recently was spotted in the Tacoma area.

“It could invade wheat fields of Eastern Washington,” said Ed Johannes, who runs a business, Deixis Consultants, which does surveys to identify mollusks for governments and businesses.

The vineyard snail already has become a problem for farmers in Australia, he said.

“It gums up the machinery,” Johannes said.

Like snails, most of the slugs you’d find in your garden have been introduced from elsewhere.

“The native slugs prefer to eat dead plant matter as opposed to green. The introduced ones from Europe love green,” Johannes said.

Disease vector

Another recent concern is snail-borne disease, such as a 2006 outbreak in China of Angiostrongylus cantonensis, or rat lungworm, that sickened 160 people.

The pathogen reproduces in rats, but some species of snails are carriers. If people get infected, the parasite causes a form of meningitis, a potentially life-threatening disease characterized by inflammation of the membranes around the brain and spinal cord.

A handful of human cases have been detected in Hawaii, Dirks said. “It’s always two guys drinking in the woods and one of them dares another to eat a snail,” she said. “I always have my students have bottles of Purell.”

In Hawaii, the pathogen is carried by a species of semi-slugs, Parmarion martensi, which have shells too small to retreat into.

The rat lungworm nematode has also been shown to infect the giant African snail (Achatina achatina), the largest snail on earth which can grow up to 7 inches long and are often smuggled into the United States as exotic (and illegal) pets.

Florida has been working to eliminate the giant African snail, which has escaped into the wild. So far there have been no cases of rat lungworm there, Robinson said, but another tropical species of snail in the state also is suspected to carry the disease.

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The fortunate thing is that the disease so far has been confined to tropical and subtropical areas. The concern is that the semi-slug could be exported to the mainland with Hawaiian agricultural products, such as cilantro.

“We’re keeping a very close eye on angiostrongylus because there have been a few cases of humans,” Robinson said.

The last line of defense

Once invasive snails get into the country and spread, gardeners find themselves on the last line of defense. They’ve developed a range of practices and techniques to control snail and slug populations.

Barb O’Brien’s scattered eggshells worked this year, but she also uses other natural techniques. Snails are drawn to a pie plate with a little beer in it. “They kind of drown and dissolve,” she said.

“I’ve been known to step on them. That’s also grisly,” she said.

Seattle author Gordon suggested changing watering practices. Watering at night gives gastropods a welcoming environment when they come out to eat, akin to running a Zamboni before a hockey game, he said.

Instead, watering in the morning gives the soil a chance to dry out and be less snail-friendly come nightfall.

Gordon also recommended raking gardens early in the season to expose the eggs to birds and the elements.

WSU Extension’s Sharon Collman said gardeners should be smart about using bait, putting it near the nests, not the food source, and coming back later to pick up the victims.

Some commercial snail bait only paralyzes the snail, and after they recover, they’ll never be fooled by the bait again, Collman said.

There is also the original, if brutal, chemical warfare agent against gastropods: salt.

“It’s a really painful death for them,” Collman said.

“I tend to favor a quick jab with the edge of a trowel, or the edge of my boot,” she said.

Chris Winters: 425-374-4165; Twitter: @Chris_At_Herald.

This story has been modified to correct the title of Barb O’Brien, secretary of the Everett Garden Club.

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Are snails invasive to Washington state? ›

Yes. New Zealand mud snails were first discovered in the lower Columbia River in 2002 and in Olympia's Capitol Lake in 2009. Other known locations are in the lower Columbia River, Long Beach peninsula, and in King County's Kelsey and Thornton Creeks and Lake Washington.

Are snails invasive in North America? ›

Background. Invasive snails include a variety of gastropods invasive to areas of North America.

What snail is invasive? ›

The Giant African Snail (Lissachatina fulica or GAS) was first found in southern Florida in the 1960s, and it took 10 years and $1 million to eradicate it. It was reintroduced in 2011, and eradication efforts were completed in Broward and Miami Dade counties in Florida in 2021.

Are snails native to Washington state? ›

The Pacific sideband (Monadenia fidelis) is a native snail, and is also the largest found in Washington, with shells up to an inch wide.

Are Grove snails invasive? ›

The Grove Snail (Cepaea nemoralis)

A native of Europe, it has also spread to North America. Fortunately, this snail is not normally interested in living plants and is therefore not a threat to horticulture or agriculture. The garden snail is becoming a pest in many parts of the world.

Are banana slugs invasive? ›

The native banana slug, Ariolimax columbianus. The invasive slug Arion rufus was introduced from Europe within the last century. Slugs are nocturnal detritivores, but little is known about the particular feeding preferences of these two species or whether they compete with each other for food.

What state has the most snails? ›

Alabama has the most diverse snail species in the U.S, making the Heart of Dixie a mollusk mecca.

Which animal eats snails? ›

Vertebrate predators of snails and slugs include shrews, mice, squirrels, and other small mammals; salamanders, toads and turtles, including the uncommon Blandings Turtle Emydoidea blandingii; and birds, especially ground-foragers such as thrushes, grouse, blackbirds, and wild turkey.

Are apple snails illegal in US? ›

Another snail on the list is the golden or channeled apple snail, a highly invasive freshwater snail that has already spread worldwide (Pomacea canaliculata). These species of snails are exceptionally restricted and unlawful for both interstate travel and importation into the United States.

What happens if you touch an African snail? ›

Giant African land snails pose a serious health risk to humans by carrying the parasite rat lungworm, known to cause meningitis in humans. The snails should not be handled without proper protection and sanitation.

Is giant African snail invasive? ›

It feeds voraciously and is a vector for plant pathogens, causing severe damage to agricultural crops and native plants. It competes with native snail taxa, is a nuisance pest of urban areas, and spreads human disease. This snail is listed as one of the top 100 invasive species in the world.

Are snails toxic to dogs? ›

When it comes to eating snails, they generally are non-toxic. But that's not to say snails can't cause problems. In fact, snail consumption can cause a major health issue in dogs: lungworm infestation. Lungworms can cause coughing as well as more severe respiratory problems, such as bronchitis or difficulty breathing.

What type of slugs live in Washington? ›

The most damaging slugs in western Washington are the 3- to 4-inch Arion ater (orange to black in Arion ater color) and the 1- to 1-1/2-inch Deroceras reticulatum (gray to brown). The native yellow “banana slug” is seldom a serious pest.

What do Oregon forest snails eat? ›

  • Range.
  • Habitat. On the South Coast BC, Oregon Forestsnail is found in broadleaf forests or mixed forests. ...
  • Diet. Oregon Forestsnail graze on and mulch herbaceous vegetation but appear to have a strong preference for Stinging Nettle, one of the plants populations are most often found in association with.
  • Life Cycle.

How much space does a snail need? ›

Space for a Snail

Snails do not take up much space. Each snail should have at least a one gallon tank to roam in. But even if you splurge for a five or ten gallon tank, this still only takes up a couple of feet of desk space.

Are leopard slugs invasive? ›

Leopard slugs, also called great gray slugs or the giant garden slug, are an invasive species to North America, having been introduced here from Europe.

Are black slugs invasive? ›

Native to Europe, the black slug is an invasive species in Australia, Canada (British Columbia, Newfoundland, Quebec), and the United States (Pacific Northwest).

What's the biggest slug in the world? ›

The world's largest species of terrestrial slug is the ash-black slug Limax cinereoniger. Found in ancient woodlands throughout all but the most northerly regions of Europe, it can grow to a length of up to 30 cm, and eats fungi.

What does licking a banana slug do? ›

A curious animal that prods the banana slug with its nose or tongue will quickly discover that the slime acts as an anesthetic. This is why banana slugs have no natural predators—and why “lick the banana slug” is a popular dare among coastal forest hikers.

Can you eat cooked slugs? ›

Terrestrial slugs and snails (found on land, not in the sea) are generally safe for human consumption, always after a thorough cooking. And their nutritional value certainly justifies the effort of collecting and preparing them.

Are orange slugs rare? ›

It's a common garden slug I believe, usually seen in black - but it does come in a variety of colours.

What snail has pink eggs? ›

Island and channeled apple snails lay “pink” eggs that turn white/ grey before hatching.

What is the largest snail on record? ›

The largest known land gastropod is the African giant snail (Achatina achatina) 🐌 The largest recorded specimen measured 39.3 cm (1 ft 3.5 in) from snout to tail when fully extended, with a shell length of 27.3 cm (10.75 in). It weighed 900 g (2 lb).

Are giant snails illegal in US? ›

USDA prohibits importing or owning the giant African Snail (GAS) because it poses a significant risk to U.S. agricultural and human health. GAS is one of the most damaging snails in the world and feeds on at least 500 types of plants, including peanuts, most varieties of beans, peas, cucumbers, and melons.

What are snails scared of? ›

Garlic, Lawn Chamomile, chives. Some plants repel most slugs and snails and these may have a deterrent effect when planted alongside or used to make an extract. Many gardeners swear by garlic as a natural pest control. Some say chives are effective it the leaves are tied around vulnerable plants; sounds fiddly.

Do snails have brain? ›

Gastropods and snails do not have brains, but their nervous systems are centralized to a certain extent, and they have analogous structures, which are several pairs of ganglia (clusters of neurons) connected by a nerve cord.

Do snails have any benefits? ›

In addition to containing significant sources of protein and low amounts of fat, snails are also good sources of iron, calcium, Vitamin A, and a number of other minerals. Vitamin A helps your immune system fight off diseases and strengthens your eyes. It also helps cells in your body grow.

What is a fire snail? ›

Platymma tweediei, often called the (Malaysian) fire snail, is the largest land snail in Peninsular Malaysia, living exclusively in the mountainous forests there. It is the only species in the genus Platymma. It is characterized by its black shell and orange to bright red foot.

Are Roman snails legal in the US? ›

Achatinine snails including the genera Achatina, Archachatina and Lissachatina (including Lissachatina fulica, the giant African snail), are specifically prohibited for both interstate movement and importation into the United States. These snails poses a threat to both humans and plants.

Are Japanese trapdoor snails invasive? ›

Japanese Trapdoor Snails are considered an invasive species, and are even illegal in some states. You will want to make sure that you check your local laws before purchasing. Japanese Trapdoor Snails are a favorite food of raccoons.

What kind of slugs are in Washington state? ›

The most damaging slugs in western Washington are the 3- to 4-inch Arion ater (orange to black in Arion ater color) and the 1- to 1-1/2-inch Deroceras reticulatum (gray to brown). The native yellow “banana slug” is seldom a serious pest.

How do I know what kind of snail I have? ›

Firstly the number of whorls can help to determine between species. The profile of the whorls and their comparative size can often help, some snails are very ventricose, others very slender, some have a huge body whorl, others have more evenly increasing whorls.

What do Pacific sideband snails eat? ›

Pacific sidebands are endemic to the Pacific Coast of North America, where they typically reside in cool, moist, shaded forests. They feed on fungi and plant material and provide prey for raccoons, shrews, and mice, among others.

What do Oregon forest snails eat? ›

  • Range.
  • Habitat. On the South Coast BC, Oregon Forestsnail is found in broadleaf forests or mixed forests. ...
  • Diet. Oregon Forestsnail graze on and mulch herbaceous vegetation but appear to have a strong preference for Stinging Nettle, one of the plants populations are most often found in association with.
  • Life Cycle.

What eats slugs in Washington State? ›

Benefits. Slugs have important ecological roles. They help cycle organic matter, which in turns helps to build healthy, rich soil. They also are food for wildlife, including raccoons, possums, garter snakes, toads, turtles, and birds.

Are orange slugs poisonous? ›

These slugs are usually black; however, some might be brown or close to orange in color. These slugs are also very common near houses and gardens. These slugs are not poisonous.

Are slugs good to eat? ›

As you may have gathered by now, it's a bad idea to eat raw slugs or snails. The same goes for raw frogs and freshwater crabs and shrimp.

What is a snails favorite food? ›

Most slugs and snails are omnivores — they can eat nearly everything. However, if they have the choice, they turn into real gourmets. For example, cucumbers, tomatoes, and wilting lettuce leaves are at the top of their list of favorite foods.

How long is a snail's pregnancy? ›

The eggs may take one to five weeks to hatch depending on water temperatures. The warmer the water, the faster the eggs will hatch. A juvenile snail is about 1/100 inch at hatching, but rap- idly grows its first year to several hundred times its birth size.

Why is my land snails shell turning white? ›

too high a co2 level can cause their shells to erode and turn white (too high of a carbonic acid level). In addition, too high of a potassium level can also cause calcium uptake problems... so even if you have calcium, if you have high potassium and high co2, it won't do much good to add more calcium.

What do BC snails eat? ›

European brown garden snail is present in Southern BC and Vancouver Island. This snail eats a wide variety of ornamental and agricultural crops and will compete with native snail and slug species for food and habitat.

Can you eat snails in Oregon? ›

You can eat almost all species of snails, clams, octopi and fish. Most aren't going to make you sick.”

Are there banana slugs in Oregon? ›

Oregon is home to one of the biggest land mollusks in the world – the banana slug (Ariolimax columbianus). These unmistakable creatures can grow six to 10 inches long.

Are slugs in Oregon poisonous? ›

While slugs are slimy and damaging to plants, they are not poisonous to humans.

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