SnailS and SlugS - Maine

Snails and Slugs

Integrated Pest Management for Home Gardeners and Landscape Professionals

Snails and slugs are among the most Snails and slugs are most active at Figure 1. Brown garden snail.
bothersome pests in many gardens and night and on cloudy or foggy days. On Figure 2. Adult white garden snail,
landscapes. The brown garden snail, Cor- sunny days they seek hiding places out Theba pisana.
nu aspersum (formerly Helix aspersa), is the of the heat and bright light. Often the Figure 3. Gray garden slugs with chew-
most common snail causing problems in only clues to their presence are their ing damage and slime trails on leaves.
California gardens (Fig. 1). It was intro- silvery trails and plant damage. In Figure 4. Tawny slug, also called yellow
duced from France during the 1850s for areas with mild winters, such as south- cellar slug.
use as food. Another troublesome snail is ern coastal locations, snails and slugs
the white garden snail, Theba pisana (Fig. can be active throughout the year.
2). It currently is established only in San
Diego County but has been found in Los During cold weather, snails and slugs
Angeles and Orange counties as well. hibernate in the topsoil. During hot,
dry periods or when it is cold, snails
Several species of slugs also cause seal themselves off with a parchment-
damage including the gray garden slug like membrane and often attach them-
(Deroceras reticulatum, formerly Agrio- selves to tree trunks, fences, or walls.
limax meticulatus) (Fig. 3), the banded
slug (Lehmannia poirieri), the three-band DAMAGE
garden slug (L. valentiana), the tawny
slug (Limacus flavus) (Fig. 4), and the Snails and slugs feed on a variety of liv-
greenhouse slug (Milax gagates). ing plants and on decaying plant matter.
They chew irregular holes with smooth
IDENTIFICATION AND edges in leaves and flowers and can clip
BIOLOGY succulent plant parts. They also can
chew fruit and young plant bark.
Both snails and slugs are members of
the mollusk phylum and are similar in Because they prefer succulent foliage or
structure and biology, except slugs lack flowers, they primarily are pests of seed-
the snail’s external, spiral shell. These lings and herbaceous plants, but they
mollusks move by gliding along on a also are serious pests of ripening fruits
muscular “foot.” This muscle constant- that are close to the ground such as
ly secretes mucus, which facilitates strawberries, artichokes, and tomatoes.
their movement and later dries to form They also will feed on foliage and fruit
the silvery “slime trail” that signals the of some trees; citrus are especially sus-
presence of either pest. ceptible to damage. Look for the silvery
mucous trails to confirm slugs or snails
All land slugs and snails are hermaph- caused the damage and not earwigs,
rodites, so all have the potential to lay caterpillars, or other chewing insects.
eggs. Adult brown garden snails lay an
average of 80 spherical, pearly white MANAGEMENT
eggs (Fig. 5) at a time into a hole in the
soil. They can lay eggs up to 6 times a A good snail and slug management pro-
year, and it takes about 2 years for snails gram relies on a combination of methods.
to mature. Slugs reach maturity after The first step is to eliminate, as much as
about 3 to 6 months, depending on the possible, all places where they can hide
species, and lay clear, oval to round eggs during the day. Boards, stones, debris,
in batches of 3 to 40 beneath leaves, in weedy areas around tree trunks, leafy
soil cracks, and in other protected areas. branches growing close to the ground,
and dense ground covers such as ivy are

P NEST OTES Publication 7427
University of California
November 2009
Statewide Integrated Pest Manage ment Program
Agriculture and Natural Resources

November 2009 Snails and Slugs

ideal sheltering spots. It won’t be possible to potential hiding places. After the Figure 5. Snail eggs.
to eliminate some shelters such as low population has noticeably declined, a
ledges on fences, the undersides of wood- weekly handpicking can be sufficient. Figure 6. This turned over board trap
en decks, and water meter boxes, so make reveals snails on its underside.
a regular practice of trapping and remov- To draw out snails and slugs, water the
ing snails and slugs from these areas. infested area in the late afternoon. After Figure 7. Copper barriers can keep snails
dark, search them out using a flashlight, and slugs out of trees and raised beds.
Locate vegetable gardens or susceptible pick them up (rubber gloves are handy
plants as far away from snail and slug when slugs are involved), place them in Barriers
hiding places as possible. Reducing hid- a plastic bag, and dispose of them in the
ing places allows fewer snails and slugs trash. You also can put them in a bucket Several types of barriers will keep
to survive. The survivors congregate in with soapy water and dispose of them snails and slugs out of planting beds.
the remaining shelters, where you can in your compost pile after they are dead. The easiest to maintain are those made
more easily locate and remove them. Alternatively, crush captured snails with copper flashing and screen. It is
and slugs and leave them in the garden. believed that copper barriers are effec-
Switching from sprinkler irrigation to Another option for killing slugs you tive because the copper reacts with the
drip irrigation will reduce humidity and have collected is to spray them with a slime that snails and slugs secrete, caus-
moist surfaces, making the habitat less solution of household ammonia diluted ing a disruption in their nervous system
favorable for these pests. Choose snail- to a 5 to 10% solution in water. similar to an electric shock. When erect-
proof plants, such as those listed below, ing vertical copper screens, it is best to
for areas where snails and slugs are Traps use ones that are at least 4 inches tall, so
dense. Copper barriers can be useful for you can bury a portion of it a few inches
protecting especially susceptible plants. You can trap snails and slugs beneath below the soil to prevent slugs from
Though baits can be part of a manage- boards or flower pots that you position crawling beneath the barrier.
ment program, it is better to use them in throughout the garden and landscape. Copper foil (e.g. Snail-Barr) wrapped
conjunction with other habitat modifica- Inverted melon rinds also make good around planting boxes, headers, or trunks
tion, especially in gardens that contain traps. Construct wooden traps using 12- (Fig. 7) will repel snails for several years.
plenty of shelter, food, and moisture. by 15-inch boards (or any easy-to-han- When banding trunks, wrap the copper
dle size) raised off the ground by 1-inch
Plant selection can greatly affect how runners (Fig. 6). The runners make it
difficult your battle with snails and easy for the pests to crawl underneath.
slugs will be. Because snails and slugs Scrape off the accumulated snails and
favor seedlings and plants with succu- slugs daily and destroy them; crushing
lent foliage, you will need to vigilantly is the most common method. Don’t use
protect these. Some plants these pests salt to destroy snails and slugs, since it
will seriously damage include basil, will increase soil salinity.
beans, cabbage, dahlia, delphinium,
hosta, lettuce, marigolds, strawberries, Some people use beer-baited traps
and many other vegetable plants. On the buried at ground level to catch and
other hand, many plants resist snail and drown slugs and snails that fall into
slug damage including begonias, Cali- them. Because it is the fermented part
fornia poppy, fuchias, geraniums, impa- of the product that attracts these pests,
tiens, lantana, nasturtiums, and purple you also can use a sugar-water and
robe cup flower as well as many plants yeast mixture instead of beer. However,
with stiff leaves and highly scented foli- these traps aren’t very effective for the
age such as lavender, rosemary, and sage. labor involved. Beer traps attract slugs
Most ornamental, woody plants, and and snails within an area of only a few
ornamental grasses also aren’t seriously feet, and you must replenish the bait
affected. If you design your landscape every few days to keep the level deep
using snail and slug resistant plants, you enough to drown the mollusks. Traps
are likely to have very limited damage. must have deep, vertical sides to keep
the snails and slugs from crawling out
Handpicking and a top to reduce evaporation. You
can purchase this type of snail and
Handpicking can be very effective if slug trap at garden supply stores.
done thoroughly on a regular basis.
At first you should look for snails and
slugs daily, paying careful attention

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November 2009 Snails and Slugs

foil around the trunk, tab side down, and problems. Be careful, though, as these Figure 8. The devil’s coach horse, Ocy-
cut it to allow an 8-inch overlap. Attach birds also can eat seedlings. pus olens, which is more than an inch
one end or the middle of the band to the long, is a predatory beetle that feeds on
trunk with one staple oriented parallel to The predatory decollate snail, Rumina de- snails and slugs.
the trunk. Overlap and fasten the ends collata, (Fig. 9) has been released in South-
with one or two large paper clips to al- ern California citrus orchards to control Figure 9. The decollate snail is a preda-
low the copper band to slide as the trunk young brown garden snails and is pro- tor of snails.
grows. Bend the tabs out at a 90° angle viding very effective biological control. It Baits containing only metaldehyde are
from the trunk. If the bands tarnish, you feeds only on small snails, not full-sized most reliable when temperatures are
can clean them with a vinegar solution. ones. Because of the potential impact of warm or during periods of lower hu-
When using copper bands on planter the decollate snail on certain endangered midity. When it is sunny or hot, these
boxes, be sure the soil within the boxes mollusk species, it can’t be released in baits cause snails and slugs to die from
is snail free before applying them. If California outside of Fresno, Imperial, desiccation or dehydration. The pests
it isn’t, handpick the snails and slugs Kern, Los Angeles, Madera, Orange, Riv- usually die with one day of ingesting
from the soil after applying the band erside, Santa Barbara, San Bernardino, the chemical or getting it on their foot.
(but before planting new plants) until San Diego, Ventura, and Tulare counties. If cool, wet weather follows the bait-
the box is free of these pests. Solarizing Decollate snails can feed on seedlings, ing, they can recover if they ingest a
the soil—a technique that uses clear, small plants, and flowers and can be a sublethal dose. Don’t water heavily for
plastic tarp and the sun’s heat—is a nuisance when they cover the back patio at least 3 or 4 days after bait placement,
good way to kill eggs in raised beds. on a misty day. Because snail baits will since watering will reduce effectiveness.
Instead of copper bands, Bordeaux kill decollate snails, you shouldn’t use Most metaldehyde baits break down
mixture (a copper sulfate and hydrated them where these predators are active. rapidly when exposed to sunlight and
lime mixture) or copper sulfate alone high irrigation; however, some paste or
brushed onto trunks will repel snails. Baits bullet formulations (e.g. Deadline) hold
One treatment should last about a year. up somewhat longer in these conditions.
Adding a commercial spreader or white Snail and slug baits can be effective Iron phosphate baits—available under
latex paint can help the Bordeaux mix- when used properly in conjunction many trade names including Sluggo
ture remain effective for two seasons. with a cultural program incorporating and Escar-Go—have the advantage
Barriers of dry ashes or other abrasives the other methods discussed above. of being safe for use around children,
heaped in a band 1 inch high and 3 However, baits alone won’t effectively domestic animals, birds, fish, and other
inches wide around the garden also can control snails or slugs. Baits are toxic to wildlife, making them a good choice
be effective. However, these barriers lose all snails and slugs, including the pred- for an integrated pest management
their effectiveness after becoming damp, atory decollate snail and native species. program in your garden. Ingesting
making them difficult to maintain and even small amounts of the bait will
not very useful in most garden situations. Several types of snail and slug bait prod- cause snails and slugs to stop feeding,
ucts are available. Baits containing the although it can take several days for
Natural Enemies active ingredient metaldehyde are most
common; however, metaldehyde baits
Snails and slugs have many natural en- are particularly poisonous to dogs and
emies including ground beetles, patho- cats, and the pelleted form is especially
gens, snakes, toads, turtles, and birds, attractive to dogs. Don’t use metaldehyde
but most are rarely effective enough snail baits where children and pets could
to provide satisfactory control in the encounter them. Metaldehyde baits con-
garden. One predator found in some taining 4% active ingredient are more
California gardens is a large Staphyli- effective than those containing only 2%;
nid beetle called the devil’s coach horse, however, they also are more toxic to dogs
Ocypus olens (Fig. 8). However, this and wildlife. Avoid getting metaldehyde
beetle, which is more than 1-inch long, bait on plants, especially vegetables.
also will feed on ripening or decaying
fruits and vegetables. Some metaldehyde products are formu-
Domesticated fowl—such as ducks, lated with carbaryl, partly to increase
geese, or chickens—kept penned in the spectrum of pests controlled such
infested areas can be effective snail as soil- and debris-dwelling insects, spi-
predators that significantly reduce ders, and sowbugs. However, carbaryl
is toxic to earthworms and soil-inhab-
iting beneficial insects such as ground
beetles, so it is better to avoid using
snail baits containing carbaryl.

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November 2009 Snails and Slugs

the snails to die. You can scatter the and Native Fauna of California. Oakland:
bait on lawns or on the soil around any Univ. Calif. Agric. Nat. Res. Publ. 8336.
vegetable, ornamental, or fruit tree that
needs protection. Iron phosphate baits Sakovich, N. J., J. B. Bailey, and T. W.
can be more effective against snails Fisher. 1984. Decollate Snails for Con-
than slugs overall and more effective trol of Brown Garden Snails in Southern
than metaldehyde during periods of California Citrus Groves. Oakland: Univ.
higher humidity. Snails and slugs tend Calif. Agric. Nat. Res. Publ. 21384. v
to hide before they die, so you won’t
see scattered empty shells or dead
snails and slugs as you would if treat-
ing them with metaldehyde.

Sprinkle baits in areas that snails and AUTHORS: M. L. Flint, UC Statewide IPM University of California scientists and other
slugs regularly frequent such as around Program, Davis/Entomology, UC Davis; and qualified professionals have anonymously peer
sprinkler heads. Placing baits repeated- C. A. Wilen, UC Statewide IPM Program, reviewed this publication for technical accuracy. The
ly in the same areas maximizes control, San Diego Co. ANR Associate Editor for Urban Pest Management
because mollusks tend to return to food managed this review process.
source sites. Never pile bait in mounds EDITOR: M. L. Fayard To simplify information, trade names of products
or clumps, especially those products have been used. No endorsement of named products
that are more hazardous, because pil- ILLUSTRATIONS: Figs. 1, 3–7 and 9, J, is intended, nor is criticism implied of similar products
ing makes bait attractive to pets and K. Clark, Fig. 2, D. Rosen; and Fig. 8, R. that are not mentioned.
children and is not as effective as sprin- Weinstein. This material is partially based upon work
kling. Thick, liquid baits might persist supported by the Extension Service, U.S. Department
better when it is rainy or in areas that of Agriculture, under special project Section 3(d),
receive sprinkler irrigation. Integrated Pest Management.

The timing of any baiting is critical; bait- Produced by UC Statewide
ing is less effective during very hot, very Integrated Pest Management Program
dry, or cold times of the year, because University of California, Davis, CA 95616
snails and slugs are less active during
these periods. Irrigate before applying a This and other Pest Notes are available at
bait to promote snail activity, and apply www.ipm.ucdavis.edu.
the bait in the late afternoon or evening.
Sprinkle bait around sprinklers, close to For more information, contact the University of University of California
walls and fences, or in other moist and California Cooperative Extension office in your Agriculture and Natural Resources Program
protected locations, or scatter it along county. See your telephone directory for addresses
areas that snails and slugs cross to get
from sheltered areas to the garden. and phone numbers, or visit http://ucanr.org/ce.cfm.

REFERENCES WARNING ON THE USE OF CHEMICALS
Pesticides are poisonous. Always read and carefully follow all precautions and safety recommendations
Dreistadt, S. H., J. K. Clark, and M. L. given on the container label. Store all chemicals in the original, labeled containers in a locked cabinet or shed,
Flint. 1994. Pests of Landscape Trees and away from food or feeds, and out of the reach of children, unauthorized persons, pets, and livestock.
Shrubs: An Integrated Pest Management Pesticides applied in your home and landscape can move and contaminate creeks, rivers, and oceans.
Guide. Oakland: Univ. Calif. Agric. Nat. Confine chemicals to the property being treated. Avoid drift onto neighboring properties, especially gardens
Res. Publ. 3359. containing fruits or vegetables ready to be picked.
Do not place containers containing pesticide in the trash or pour pesticides down the sink or toilet. Either use
Flint, M. L. 1998. Pests of the Garden and the pesticide according to the label, or take unwanted pesticides to a Household Hazardous Waste Collection
Small Farm: A Grower’s Guide to Using site. Contact your county agricultural commissioner for additional information on safe container disposal and
Less Pesticide. 2nd ed. Oakland: Univ. for the location of the Household Hazardous Waste Collection site nearest you. Dispose of empty containers
Calif. Agric. Nat. Res. Publ. 3332. by following label directions. Never reuse or burn the containers or dispose of them in such a manner that
they may contaminate water supplies or natural waterways.
Koehler, C. and W. Barclay. 1983. Snail
Barriers. California Agriculture 37(9-10):15. NONDISCRIMINATION STATEMENT
The University of California prohibits discrimination or harassment of any person on the basis of race,
McDonnell, R., T. Paine, and M. J. Gor- color, national origin, religion, sex, gender identity, pregnancy (including childbirth and medical conditions
mally. 2009. Slugs: A Guide to the Invasive related to pregnancy or childbirth), physical or mental disability, medical condition (cancer-related or
genetic characteristics), ancestry, marital status, age, sexual orientation, citizenship, or service in the
uniformed services (as defined by the Uniformed Services Employment and Reemployment Rights Act of
1994: service in the uniformed services includes membership, application for membership, performance of
service, application for service, or obligation for service in the uniformed services) in any of its programs
or activities.
University policy also prohibits reprisal or retaliation against any person in any of its programs or activities
for making a complaint of discrimination or sexual harassment or for using or participating in the investigation
or resolution process of any such complaint.
University policy is intended to be consistent with the provisions of applicable State and Federal laws.
Inquiries regarding the University’s nondiscrimination policies may be directed to the Affirmative Action/
Equal Opportunity Director, University of California, Agriculture and Natural Resources, 1111 Franklin Street,
6th Floor, Oakland, CA 94607, (510) 987-0096.

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