Snails and Slugs- Department of Entomology at Texas A&M University - Extension Publications
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EEE-00026
June 2005

Snails and Slugs

J. A. Jackman
Professor and Extension Entomologist

Introduction
Many land snails and slugs are pests in landscapes, vegetable gardens and greenhouses when they feed on plants. They feed directly on foliage and fruit which is the main concern and damage from these molluscs can be severe. Their preference for succulent foliage makes them serious pests of seedlings, herbaceous plants, and fruit ripening close to the ground, e.g., tomatoes and strawberries. The most destructive snails and slugs are often introduced exotic species.

Snails and slugs may be difficult to detect because they are active primarily at night. However, they leave slime trails where they crawl which can be a clue to their presence. Their soft bodies and slimy appearance make them repulsive to many people, but actually they are quite fascinating creatures. Snails and slugs are best managed with a combination of tactics.

Description
Both slugs and snails have fleshy, soft, slimy legless bodies that range in color from whitish-yellow to black; most are mottled with shades of gray. Their eyes are carried on the ends of stalks or appendages on the head. The species in Texas grow to lengths of about ½ inch to 4 inches (1.25 cm to 10 cm).

Snails and slugs have similar bodies and both are protected by the mucus that they. secrete. Snails have a hard spiral shell on their backs while slugs lack external shells completely. Shells in Texas snails range from about 1/4 inch to over 3 inches (0.62 to 7.5 cm) in diameter, and are usually off-white to brown or black in color. Snail shells provide protection from predators and during periods of excessive heat and dryness.

Biology and Habits
Land snails and slugs lay masses of eggs on substrates like plants or in the soil. Their eggs are globular and often gelatinous, and can be very tough and resistant to heat, cold and drying. Under favorable conditions eggs will hatch in about 1 month. Immediately upon hatching the young begin to feed and can reach sexual maturity in three to five months. Most snails and slugs that hatch in the spring can begin egg laying in the fall. There is a tendency for young slugs and snails to stay close to the place where they were hatched and return there each morning. Some snails may take 2 years to become full grown.

Snails and slugs require some moisture for survival. However, many snails are capable of living well in relatively dry conditions. They normally hide during the day to avoid the sun and can be found under pieces of wood, plants, pottery, rocks, fallen leaves or mulch. They are active at night or on damp, dark days. Snails and slugs are able to move easily over almost any object. They can climb trees or the side of a building.
These pests feed on leaves, flowers, stems or roots of plants by scraping off the tissue or eating holes in the leaves or flowers. Their slime trails may remain for days on rocks, sidewalks or the painted siding of houses.

Management
Snails and slugs are best managed with a combination of tactics. Habitat modification, trapping, handpicking, barriers, and baits are all management options.

Insofar as practical, eliminate or decrease snail and slug habitats by decreasing the amount of debris, compost or other hiding places. Hiding places often can be located by following slime trails. Limiting the amount of moisture, by reducing irrigation may discourage snails and slugs.

Snails and slugs can be handpicked and destroyed. Look for them under flower pots and under pot rims too. It may be possible to collect snails and slugs directly on plants at night. Inspect nursery or vegetable plants when moving them into the landscape and avoid transplants that are known to harbor snails and slugs. 

Snails and slugs can be trapped with a variety of traps. Check the traps and destroy snails and slugs every day or two. Homemade or commercial traps can be used. The trap can be passive shelters or baited traps. A piece of shingle or small board slightly elevated will serve as a shelter where snails and slugs will hide. Baited traps can be made with a saucer or jar lid. Baited traps should allow the snails and slugs to enter the trap but have difficulty leaving. Thus a straight sided trap buried with the sides at ground level would be a good design to allow them to enter the trap and have difficulty leaving. Beer is commonly used attractant and supposedly drowns them. Commercial traps for snails and slugs are available such as “The Pit”® by Surefire®, and Slug Saloon®.

Snail and slug barriers usually are made of strips, foil, or screens made of copper. Copper barriers are believed to create an electrical current when they react to snail or slug secretions. Copper bands of one inch or wider can be used as barriers around tree trunks or plant beds. Copper barrier tape with an adhesive back is sold commercially, e.g., Surefire® Products.

Aquatic habitats are special situations. Copper sulfate is a liquid that is used to control snails in aquaria and ponds. Read the product label for directions on how to calibrate the application of these products.
Diatomaceous earth is sometimes suggested for snail and slug management. This may be effective in certain situations but will wash into the soil after a rain and become ineffective.

The nematode, Heterorhabditis marelatus, also kills slugs. It is sold by Integrated Biocontrol Systems, Inc. as GrobStake®. Link: http://www.nematodary.com/

If further control measures are needed, use a commercially prepared snail and slug bait product. Many snail and slug baits contain metaldehyde as the active ingredient. Metaldehyde causes paralysis and the mollucs die from dehydration. However, under cool and wet conditions when they are most troublesome, snails and slugs may recover. Some products may also contain carbaryl (Sevin®). Iron phosphate is the active ingredient in Sluggo® and Escar-Go® baits. Iron phosphate is considered safer than metaldehyde around children, pets, and wildlife. Apply bait products as directed on the label. Baits should be distributed just after a rain or after the garden is watered because this is when snails and slugs are more active. Baits should never be used directly on vegetables unless that use is specifically stated on the label. Use baits around the edges of gardens if needed.

Snails of Particular Interest

Brown garden snail, Cornu aspersum (previously placed in Helix and Cryptomphalus)
This introduced exotic species is a stout bodied snail with a short spire. Coloration is highly variable. The general color is various shades of brown with lighter stripes around the shell. Dead, weathered shells can be very white in color.

It is a general plant feeder that may attack almost any landscape plant. Brown garden snail is a serious pest of citrus in California and frequently climbs the trees to feed. It is relocated with landscape plants particularly potted plants and consequently can occur in almost any urban community. It has been reported from most major metropolitan areas in Texas. It is regulated as a pest by the Texas Department of Agriculture. Nevertheless, brown garden snails are raised as a human food and sold as escargot.

Other exotic land snails are also garden pests in Texas. Milk snail, Otala lactea, is often common in many parts of Texas, particularly in urban areas, and chocolate-banded snail, Eobania vermiculata, has populations in central and southeastern Texas. Both are closely related to brown garden snail, but are slightly smaller in size. Both have also been used as escargot.

Decollate snail, Rumina decollata
This exotic snail is generally a uniform brown or tan color. The shell is about an inch long and elongate, and the tip of older snails is often broken off. It is transported in nursery stock and may accompany the brown garden snail in landscape plantings. The decollate snail is sometimes promoted as a biological control agent to feed on the brown garden snail. However, the use of Rumina decollata as a biological control agent should be considered carefully. It feeds on plants too, so it can become a plant pest even if it is beneficial as a predator on other snail pests.

Rosy wolfsnail, Euglandia rosae, and related wolfsnails.
Unlike most other land snails, rosy wolfsnail and its relatives are predatory and actively find and consume other snails and slugs. Although introduced rosy wolfsnails have become major ecological pests in Hawaii and other Indo-Pacific islands, the species is native to southeastern Texas. Other species occur elsewhere in the state. Rosy wolfsnail has a spindle-shaped shell that reaches about 1.5 inches in length and is pink in color; other species are smaller and tan to white. The shell opening is long and slender (not rounded as in many land snails). Learn to recognize wolfsnails to avoid harming them.

Applesnails, Pomacea spp.
Some species of applesnails are large approaching the size of a human fist. They are generally solid dark brown, with black and tan banding. Some strains are gold, yellow, white, blue or ivory in color. They live primarily in water, but have both gills and lung-like structures that allow them to feed both in the water and on land. They lay large clusters of pink, orange, or red eggs on solid objects above the waterline. Applesnails are used as human food and aquarium pets, but some species may carry harmful parasite or eat aquarium plants.

There are several species imported or established in the U.S., but the channeled applesnail, Pomacea canaliculata, and its relatives with channeled shells, Pomacea canaliculata-group, are of most concern. Applesnails with channeled shells are now established in six counties in southeastern Texas. They are pests in aquatic ecosystems and some species are considered serious pests of rice. These snails are usually called “golden apple snails” outside the U.S.

Applesnails are considered invasive species so possession, sale, transport and release of specimens is regulated by various agencies in the U.S. Texas Parks and Wildlife Department currently prohibits true channeled applesnails, P. canaliculata, but may soon expand its restrictions to all applesnails except spiketop applesnail, P. bridgesii. Spiketop applesnail is sold in the pet trade as “mystery snail,” but it is not cold tolerant and does not harm plants.

Snails for Human Consumption
Growing snails for human consumption usually involves the brown garden snail and milk snail. Sometimes these snails can be collected in the wild and used for personal consumption. There is a limited market for live snails and unless you are sure you can sell them it is not wise to start a production operation. Few operations are actually successful in the long run. Snail production is regulated by various government agencies so be sure to investigate the regulations before venturing into this business. Possession and production of this species is regulated in the US because of its pest status. Be sure to check on regulations before starting a production operation. Snails like brown garden snail, milk snail, and species of applesnails can carry parasites that are harmful to humans. Any snails prepared for human consumption should be handled carefullly and thoroughly cooked.

Contacts
Texas Parks and Wildlife Department is the regulating authority on aquatic snails. Agricultural pests are regulated by Texas Department of Agriculture and USDA-Animal Plant Health Inspection Service-Plant Protection and Quarantine.

Acknowledgements
The author thanks Robert G. Howells, Texas Parks and Wildlife Department for editorial assistance and images used in this manuscript.

Insecticide label clearances are subject to change and changes may have occurred since this publication was authored. The pesticide USER is always responsible for the effects of pesticides on his/her own plants or household goods as well as problems caused by drift from his/her property to other properties or plants. Always read and follow carefully the instructions on the container label.

The information given herein is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by the Texas Cooperative Extension is implied.

Images

Decollate snail. Photo by Robert Howells.

Pomacea canaliculata

Pomacea bridgesii. Photo by Robert Howells.

Otala lactea. Photo by Robert Howells.

Rumina decollata. Photo by Robert Howells.

Pomacea sp. Photo by Robert Howells

Pomacea canaliculata-complex. Photo by Robert Howells.

Eobania vermiculata, Chocolate banded snail.  Photo by Robert Howells.

Euglandinda rosae. Rosy wolfsnail.  Photo by Robert Howells.