BROWN GARDEN SNAIL, EMERGING PLANT PEST IN THE GEM STATE The Idaho State Department of Agriculture has confirmed the presence of the invasive garden pest known as the Brown Garden Snail (BGS) (Cryptomphalus aspersus) in several locations throughout Idaho. Last summer, the department called on the public to search for the snail after it was discovered in high numbers at the Idaho Botanical Garden in Boise in August. Newspapers and television stations from all over Idaho carried stories about the snail, along with pictures provided by the ISDA. Afterwards, the department received more than 75 phone calls and e-mails. As a result, the Brown Garden Snail (BGS) has been confirmed at more than 22 locations, including Boise, Coeur d’Alene, Eagle, Hagerman and Lewiston. Anecdotal reports from Boise homeowners indicate some citizens have suffered snail infestations for over five years. Now it is clear this snail has been unintentional introduced to several locations in the state. “We really appreciate the public’s response to this story, and we thank the media for getting the word out,” said Ben Simko, an ISDA entomologist. “As a result of the publicity on this issue, we’ve been able to develop a more accurate map of the statewide distribution of BGS. We are also beginning to gauge the magnitude of the problem particularly for the Treasure Valley were most of the confirmed infestation occur.” As an emerging plant pest there are still unanswered questions about the pest’s long term adaptability to Idaho’s environments and how severely the species will impact both urban landscapes and the nursery industry. As part of the eradication effort, ISDA is asking nurseries in the state to step up their efforts to look for this invasive species, especially because nurseries are considered a primary distributor of BGS. The snail and its eggs are easily transported in soils and plant stock. The snail is a widely distributed species that is native to Western Europe and those countries bordering the Mediterranean Basin. The primary introduction impacting the western U.S. is the reported establishment of BGS into California during 1850-1860. The snail is so destructive that it costs the state of California up to $10 million a year in agricultural losses and control measures. That’s why the Idaho State Department of Agriculture is asking for help from the nursery industry to locate snail infestations, help with eradication efforts, and slow down the snail’s spread on infested plant material. The snail will feed on a wide variety of plant species. A reproductively-active snail can produce upwards of 200 eggs. Some research has found that the snail will lay eggs as often as once a month, producing 400 eggs a year.” These snails are very destructive. They chew holes in fruit, leaves,

January 2006

flowers and other plant parts,” said Simko. “With education and the public’s vigilance, we hope to more aggressively control the pest and its spread throughout the state. Nurseries will have to be especially vigilant, according to Dr. David Robinson of the U.S. Department of Agriculture.” Nursery stock infested with this snail is often shipped from California to nurseries across the country,” said Robinson, a malacologist. Robinson also notes that this snail is very hardy, and has proven its adaptability under the most severe conditions. The snail has been known to survive harsh winters by burrowing into compost heaps. Notes Robinson: “Its current world distribution ranges from the humid tropics of South America, West Africa and eastern Asia to the cool boreal climate of southern Scandinavia. The only discernible limiting factor in its distribution so far seems to be its inability to survive extreme dry conditions. Shrub beds, ground cover and vegetable gardens are popular places for the snails, which are active at night and prefer the shade of large vine plants such as pumpkin and squash. Their presence can often be detected by plant damage and thin slime trails (versus a thicker slim trail often left by slugs.) A mature snail can measure up to 1 ½ inches in diameter. The snail has been known to live an average of four years. Safe control of the Brown Garden Snail is possible using products containing metaldehyde or iron phosphate. Home gardeners can purchase both products at home improvement, landscaping and garden stores. Homeowners are advised to always read and follow pesticide label instructions. Handpicking of the snail and setting of traps are also good ways to control garden infestations. Developmental stages of brown garden snail

January 2006

PEST NOTES Publication 7427

University of California

Agriculture and Natural Resources Revised May 2003

SNAILS AND SLUGS

Integrated Pest Management for Home Gardeners

Snails and slugs are among the mostbothersome pests in many garden andlandscape situations. The brown gardensnail (Helix aspersa) (Fig. 1), is the mostcommon snail causing problems inCalifornia gardens; it was introducedfrom France during the 1850s for use asfood.

Several species of slugs are frequentlydamaging, including the gray gardenslug (Agriolimax reticulatum) (Fig. 2), thebanded slug (Limax marginatusi), thetawny slug (Limax flavus), and thegreenhouse slug (Milax gagates). Bothsnails and slugs are members of themollusk phylum and are similar instructure and biology, except slugs lackthe snail’s external spiral shell.

IDENTIFICATION ANDBIOLOGYSnails and slugs move by gliding alongon a muscular “foot.” This muscle con-stantly secretes mucus, which laterdries to form the silvery “slime trail”that signals the presence of either pest.Slugs and snails are hermaphrodites, soall have the potential to lay eggs. Adultbrown garden snails lay about 80spherical, pearly white eggs at a timeinto a hole in the topsoil. They may layeggs up to six times a year. It takesabout 2 years for snails to mature. Slugsreach maturity after about 3 to 6months, depending on species, and layclear oval to round eggs in batches of 3to 40 under leaves, in soil cracks, and inother protected areas.

Snails and slugs are most active at nightand on cloudy or foggy days. On sunnydays they seek hiding places out of theheat and bright light; often the only

clues to their presence are their silverytrails and plant damage. In mild-winterareas such as southern coastal locations,young snails and slugs can be activethroughout the year.

During cold weather, snails and slugshibernate in the topsoil. During hot, dryperiods or when it is cold, snails sealthemselves off with a parchmentlikemembrane and often attach themselvesto tree trunks, fences, or walls.

DAMAGESnails and slugs feed on a variety ofliving plants as well as on decayingplant matter. On plants they chew ir-regular holes with smooth edges inleaves and flowers and can clip succu-lent plant parts. They can also chewfruit and young plant bark. Becausethey prefer succulent foliage or flowers,they are primarily pests of seedlingsand herbaceous plants, but they are also

serious pests of ripening fruits, such asstrawberries, artichokes, and tomatoes,that are close to the ground. However,they will also feed on foliage and fruitof some trees; citrus are especially sus-ceptible to damage. Look for the silverymucous trails to confirm damage wascaused by slugs or snails and not ear-wigs, caterpillars, or other chewinginsects.

MANAGEMENTA good snail and slug managementprogram relies on a combination ofmethods. The first step is to eliminate,to the extent possible, all places where

Figure 1. Brown garden snail.

Figure 2. Gray garden slug.

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May 2003 Snails and Slugs

snails or slugs can hide during the day.Boards, stones, debris, weedy areasaround tree trunks, leafy branchesgrowing close to the ground, and denseground covers such as ivy are idealsheltering spots. There will be sheltersthat are not possible to eliminate—e.g.,low ledges on fences, the undersides ofwooden decks, and water meter boxes.Make a regular practice of trapping andremoving snails and slugs in theseareas. Also, locate vegetable gardens orsusceptible plants as far away as pos-sible from these areas. Reducing hidingplaces allows fewer snails and slugs tosurvive. The survivors congregate inthe remaining shelters, where they canmore easily be located and removed.Switching from sprinkler irrigation todrip irrigation will reduce humidityand moist surfaces, making the habitatless favorable for these pests. Choosesnail-proof plants for areas where snailsand slugs are dense. Copper barrierscan be useful for protecting especiallysusceptible plants. Though baits can bepart of a management program forsnails and slugs, by themselves theydon’t provide adequate control in gar-dens that contain plenty of shelter,food, and moisture.

Choice of plant can greatly affect howdifficult your battle with snails andslugs will be. Snails and slugs favorseedlings and plants with succulent

foliage and these plants must be vigi-lantly protected. Some plants that areseriously damaged include basil, beans,cabbage, dahlia, delphinium, hosta,lettuce, marigolds, strawberries, andmany vegetable plants. On the otherhand, many plants resist damage fromsnails and slugs including begonias,California poppy, fuchias, geraniums,impatiens, lantana, nasturtiums, andpurple robe cup flower, and manyplants with stiff leaves and highlyscented foliage like lavender, rosemary,and sage. Most ornamental woodyplants and ornamental grasses are alsonot seriously affected. If you designyour landscape using plants like these,you are likely to have very limiteddamage from snails and slugs.

HandpickingHandpicking can be very effective ifdone thoroughly on a regular basis. Atfirst it should be done daily. After thepopulation has noticeably declined, aweekly handpicking may be sufficient.To draw out snails, water the infestedarea in the late afternoon. After dark,search them out using a flashlight, pickthem up (rubber gloves are handywhen slugs are involved), place them ina plastic bag, and dispose of them in thetrash; or they can be put in a bucketwith soapy water and then disposed ofin your compost pile. Alternatively,captured snails and slugs can be

crushed and left in the garden. House-hold ammonia diluted to a 5 to 10%solution in water can also be sprayed oncollected slugs to kill them.

TrapsSnails and slugs can be trapped underboards or flower pots positionedthroughout the garden and landscape.Inverted melon rinds make good traps.You can make traps from 12" x 15"boards (or any easy-to-handle size)raised off the ground by 1-inch runners(Fig. 3). The runners make it easy forthe pests to crawl underneath. Scrapeoff the accumulated snails and slugsdaily and destroy them. Crushing is themost common method of destruction.Do not use salt to destroy snails andslugs; it will increase soil salinity.

Beer-baited traps have been used totrap and drown slugs and snails; how-ever, they are not very effective for thelabor involved. Beer traps attract slugsand snails within an area of only a fewfeet, and must be refilled every fewdays to keep the level deep enough todrown the mollusks. Traps are buriedat ground level, so the mollusks easilyfall into them. It is the fermented prod-uct that attracts them and a sugar-waterand yeast mixture can be used in placeof beer. Traps must have deep, verticalsides to keep the snails and slugs fromcrawling out and a top to reduce evapo-ration. Snail and slug traps can also bepurchased at garden supply stores.

BarriersSeveral types of barriers will keep snailsand slugs out of planting beds. Theeasiest to maintain are those made withcopper flashing and screen. Copperbarriers are effective because it isthought that the copper reacts with theslime that the snail or slug secretes,causing a flow of electricity. Verticalcopper screens can be erected aroundplanting beds. The screen should be 6inches tall and buried several inchesbelow the soil to prevent slugs fromcrawling through the soil beneath thebarrier.

Copper foil (for example, Snail-Barr)can be wrapped around planting boxes,

Figure 3. A snail trap can be made from a board with 1-inch strips.

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headers, or trunks to repel snails forseveral years. When banding trunks,wrap the copper foil around the trunk,tab side down, and cut it to allow an8-inch overlap. Attach one end or themiddle of the band to the trunk withone staple oriented parallel to the trunk.Overlap and fasten the ends with one ortwo large paper clips to allow the cop-per band to slide as the trunk grows.Bend the tabs out at a 90° angle from thetrunk. The bands need to be cleanedoccasionally with a vinegar solution.When using copper bands on planterboxes, be sure the soil within the boxesis snail-free before applying bands. If itis not, handpick the snails and slugsfrom the soil after applying the banduntil the box is free of these pests.

Instead of copper bands, Bordeauxmixture (a copper sulfate and hydratedlime mixture) or copper sulfate alonecan be brushed on trunks to repelsnails. One treatment should last abouta year. Adding a commercial spreaderor white latex paint may increase thepersistence of Bordeaux mixturethrough two seasons. Barriers of dryashes or diatomaceous earth, heaped ina band 1 inch high and 3 inches widearound the garden, have also beenshown to be effective. However, thesebarriers lose their effectiveness afterbecoming damp and are therefore diffi-cult to maintain and not very useful inmost garden situations.

Natural EnemiesSnails and slugs have many naturalenemies, including ground beetles,pathogens, snakes, toads, turtles, andbirds, but most are rarely effectiveenough to provide satisfactory controlin the garden. An exception is the use ofdomesticated fowl—ducks, geese, orchickens—kept penned in infested ar-eas. (Be careful, though, as these birdsmay also eat seedlings.) The predaceousdecollate snail (Rumina decollata) hasbeen released in southern Californiacitrus orchards for control of the browngarden snail and is providing very ef-fective biological control. It feeds onlyon small snails, not full-sized ones.Because of the potential impact of thedecollate snail on certain endangered

mollusk species, it cannot be released inCalifornia outside of Fresno, Imperial,Kern, Los Angeles, Madera, Orange,Riverside, Santa Barbara, San Bernar-dino, San Diego, Ventura, or Tularecounties. Also, decollate snails mayfeed on seedlings, small plants, andflowers as well as be a nuisance whenthey cover the back patio on a mistyday. Decollate snails will be killed bysnail baits.

BaitsSnail and slug baits can be effectivewhen used properly in conjunctionwith a cultural program incorporatingthe other methods discussed above.However, baits alone will not effec-tively control snails or slugs. Severaltypes of snail and slug bait products areavailable. Baits containing the activeingredient metaldehyde are most com-mon. Metaldehyde baits are particu-larly poisonous to dogs and cats, andthe pelleted form is especially attractiveto dogs. Metaldehyde snail baits shouldnot be used where children and petscannot be kept away from them. Somemetaldehyde products are formulatedwith carbaryl, partly to increase thespectrum of pests controlled to includesoil and debris-dwelling insects, spi-ders, and sowbugs. However, carbarylis toxic to soil-inhabiting beneficials likeground beetles and earthworms andshould be avoided if snail and slugmanagement is all that is required.Metaldehyde baits containing 4%metaldehyde are significantly moreeffective than those products containingonly 2% metaldehyde; however, theyare also more toxic to dogs and wildlife.Most currently available 4% productsare formulated for use in enclosed baitstations to minimize their hazard.

Avoid getting metaldehyde bait onplants, especially vegetables. Baits con-taining only metaldehyde are mostreliable when temperatures are warmor following a rain when snails andslugs are active. Metaldehyde does notkill snails and slugs directly unless theyeat a substantial amount; rather, itstimulates their mucous-producing cellsto overproduce mucous in an attemptto detoxify the bait. The cells eventually

fail and the snail dies. When it is sunnyor hot, they die from desiccation. Ifbaiting is followed by cool and wetweather, they may recover if they ingesta sublethal dose. Do not water heavilyfor at least 3 or 4 days after bait place-ment; watering will reduce effective-ness and snails may recover frommetaldehyde poisoning if high mois-ture conditions occur. Most metalde-hyde baits break down rapidly whenexposed to sunlight; however, somepaste or bullet formulations (such asDeadline) hold up somewhat longerunder conditions of sunlight andmoisture.

A recently registered snail and slugbait, iron phosphate (available undermany trade names including Sluggoand Escar-Go), has the advantage ofbeing safe for use around domesticanimals, children, birds, fish, and otherwildlife and is a good choice for a gar-den IPM program. Ingestion of the ironphosphate bait, even in small amounts,will cause snails and slugs to ceasefeeding, although it may take severaldays for the snails to die. Iron phos-phate bait can be scattered on lawns oron the soil around any vegetables, orna-mentals, or fruit trees to be protected.Iron phosphate baits may be more effec-tive against snails than slugs.

Sprinkle baits in areas that snails andslugs regularly frequent such as areasaround sprinkler heads. Placing baitsrepeatedly in the same areas maximizescontrol because molluscs tend to returnto food source sites. Never pile bait inmounds or clumps, especially thosebaits that are hazardous, because pilingmakes a bait attractive to pets and chil-dren. Placement of the bait in a com-mercial bait trap reduces hazards topets and children and can protect baitsfrom moisture, but may also reducetheir effectiveness. Thick liquid baitsmay persist better under conditions ofrain and sprinklers.

The timing of any baiting is critical;baiting is less effective during very hot,very dry, or cold times of the year be-cause snails and slugs are less activeduring these periods. Irrigate before

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May 2003 Snails and Slugs

For more information contact the University

of California Cooperative Extension or agri-

cultural commissioner’s office in your coun-

ty. See your phone book for addresses and

phone numbers.

AUTHOR: M. L. Flint

EDITOR: B. Ohlendorf

TECHNICAL EDITOR: M. L. Flint

DESIGN AND PRODUCTION: M. Brush

ILLUSTRATIONS: Figs. 1 & 2: Seventeenth

Street Studios. Fig. 3: DANR Leaflet 2530.

Produced by IPM Education and Publica-

tions, UC Statewide IPM Program, Universi-

ty of California, Davis, CA 95616-8620

This Pest Note is available on the World

Wide Web (http://www.ipm.ucdavis.edu)

This publication has been anonymously peer re-viewed for technical accuracy by University of Cal-ifornia scientists and other qualified professionals.This review process was managed by the ANR

Associate Editor for Pest Management.

To simplify information, trade names of productshave been used. No endorsement of named productsis intended, nor is criticism implied of similar productsthat are not mentioned.

This material is partially based upon worksupported by the Extension Service, U.S. Departmentof Agriculture, under special project Section 3(d),Integrated Pest Management.

WARNING ON THE USE OF CHEMICALSPesticides are poisonous. Always read and carefully follow all precautions and safety recommendations

given on the container label. Store all chemicals in the original labeled containers in a locked cabinet or shed,away from food or feeds, and out of the reach of children, unauthorized persons, pets, and livestock.

Confine chemicals to the property being treated. Avoid drift onto neighboring properties, especiallygardens containing fruits or vegetables ready to be picked.

Do not place containers containing pesticide in the trash nor pour pesticides down sink or toilet. Eitheruse the pesticide according to the label or take unwanted pesticides to a Household Hazardous WasteCollection site. Contact your county agricultural commissioner for additional information on safe containerdisposal and for the location of the Household Hazardous Waste Collection site nearest you. Dispose ofempty containers by following label directions. Never reuse or burn the containers or dispose of them in sucha manner that they may contaminate water supplies or natural waterways.

The University of California prohibits discrimination against or harassment of any person employed by orseeking employment with the University on the basis of race, color, national origin, religion, sex, physicalor mental disability, medical condition (cancer-related or genetic characteristics), ancestry, marital status,age, sexual orientation, citizenship, or status as a covered veteran (covered veterans are special disabledveterans, recently separated veterans, Vietnam-era veterans, or any other veterans who served on activeduty during a war or in a campaign or expedition for which a campaign badge has been authorized).University policy is intended to be consistent with the provisions of applicable State and Federal laws.Inquiries regarding the University’s equal employment opportunity policies may be directed to theAffirmative Action/Staff Personnel Services Director, University of California, Agriculture and NaturalResources, 300 Lakeside Drive, 6th Floor, Oakland, CA 94612-3550, (510) 987-0096.

applying a bait to promote snail activ-ity and apply the bait in the late after-noon or evening. Application on awarm, humid evening is ideal. Applybait in a narrow strip around sprin-klers, close to walls and fences or inother moist and protected locations, orscatter it along areas that snails andslugs cross to get from sheltered areasto the garden.

REFERENCESDreistadt, S. H., J. K. Clark, and M. L.Flint. 1994. Pests of Landscape Trees andShrubs: An Integrated Pest ManagementGuide. Oakland: Univ. Calif. Agric. Nat.Res. Publ. 3359.

Flint, M. L. 1998. Pests of the Garden andSmall Farm: A Grower’s Guide to UsingLess Pesticide. 2nd ed. Oakland: Univ.Calif. Agric. Nat. Res. Publ. 3332.

Hesketh, K. A., and W. S. Moore. 1979.Snails and Slugs in the Home Garden.Oakland: Univ. Calif. Agric. Nat. Res.Leaflet 2530.

Sakovich, N. J, J. B. Bailey, and T. W.Fisher. 1984. Decollate Snails for Controlof Brown Garden Snails in Southern Cali-fornia Citrus Groves. Oakland: Univ.Calif. Agric. Nat. Res. Publ. 21384.