Slugs and snails
What are they?
Slugs and snails are molluscs, like oysters and clams. They are both similar in structure, except that the snail is protected by a hard shell that makes it less vulnerable than slugs to dry conditions and the sun.
Slugs and snails have a soft, unsegmented body that is 2 to 4 cm (.79 to 1.5 inches) long. The head has one or two pairs of tentacles. The front tentacles are sensitive to odours and sometimes taste, while each of the larger back tentacles have an eye at the end.
Slugs and snails are known as gastropods, which means "stomach foot." The foot located on the stomach is how they move around. Slugs and snails are also hermaphrodites, with both male and female organs. Snails have an external shell large enough to cover the entire animal, helping them to survive severe drought and heat.
Should I be concerned?
When slugs and snails invade vegetable or herb gardens, they can cause major damage, eating up to 40 percent of their weight in a day. Slugs and snails attack seedlings, roots, tubers, and young plants, leaving large jagged holes and sticky silvery deposits, mainly on the leaves of herbs and garden vegetables.
In spring, soft sounds can be heard from slugs and snails under shrubs whose leaves are coming out. The animals crawl out of their winter shelter in search of damp surroundings where they can live. Moisture and mulch encourage slugs and snails to multiply.
How do I know if I have a problem?
During the day, slugs and snails hide in cool, dark places: under dead leaves, lumps of earth, rocks, mulch, and wooden boards. When dusk falls, they come out from their shelters in search of food. They are also more active under cloudy conditions or after a light rain. Their active period is from about April to October, and then they hibernate until the next spring.
How can I get rid of slugs and snails?
To prevent slugs and snails from invading vegetable gardens, it is important to remove all decaying vegetables and other sources of food, as well as bricks, boards, and piles of debris that are directly in contact with the soil. It is also a good idea to rake fallen leaves and to thin plants so the sun can get through more easily.
Snail and slug removal
When snails are faced with difficult living conditions, they react by sealing the opening of their shells with a mucus sheet (known as an operculum), which soon hardens to a leathery texture. The snails can then become dormant, and can remain this way for up to four years.
- Hand picking is most effective in the evening, about two hours after sunset, since slugs and snails are more active at night. Using a flashlight, check the base of plants, the back of leaves and between rows in your herb or vegetable garden. Use a spoon to dislodge the pests and then place them in a container of soapy water or rubbing alcohol to kill them. Although labour intensive, one hour of hand picking will noticeably reduce snail and slug populations.
- You may also trap slugs and snails by creating an ideal shelter for them in a cool dark location. Place melon or grapefruit peel or inverted flower pots in the garden, leaving space so that the pests can enter the shelter. Wooden boards or asphalt shingles covered with aluminum foil may also be used as traps. Simply place them along the plant rows with the foil side on top and nail the centre of the boards or shingles to the ground, so they are secure. During the day, slugs and snails will take shelter underneath the board or shingle to get away from the sun. Check traps daily, and kill any slugs and snails by putting them in soapy water or rubbing alcohol.
- To attract and drown slugs and snails, fill a shallow container with about 2.5 cm (1 inch) of stale beer and place it so that the top edge is at ground level. Space containers 3 metres (10 ft.) apart throughout the garden. Place these traps early in the evening when feeding activity begins, and empty them regularly.
- Slugs and snails have natural enemies. Thetoad is the most important, but snakes, several species of ground beetles and their larvae, wild birds, and ducks will also eat slugs and snails. Encourage these predators to live in your garden to maintain a natural balance.
- Barriers are an effective way to get rid of slugs and snails. Sprinkle a decent amount of sand, wood ashes, or crushed eggshells at the base of plants. These substances irritate the bodies of slugs and snails and discourage them from climbing onto the plants to feed. Copper flashings about 5 cm high may also be installed around the borders of your garden. Copper gives off a small electric charge that keeps slugs and snails away. Strips of aluminum mosquito screening (about 7.5 cm high and inserted 2.5 cm deep in the ground) can also be placed around the garden.
If you use a pesticide to control your pest problem, read the label to make sure you are choosing the right product for the right pest. Follow all label directions and warnings carefully. Always look for a Pest Control Products (PCP) number on the label so you know the product has been approved by Health Canada. See Use pesticides safely for more information on using pesticides safely
- Diatomaceous earth is a fine powder (also known as silicon dioxide) that is made up of crushed microscopic marine fossils. Apply by lightly coating or dusting places where slugs and snails hide, like in garden rows or under the leaves. As the slugs or snails crawl over the fine powder, their outer protection is scratched, causing them to dehydrate and die. Diatomaceous earth is non-toxic to humans and pets, but you should avoid breathing in the dust. It will remain active as long as it is kept dry.
- Chemical control products are sold under several trade names in garden supply and hardware stores, in the form of pellets or powders.
- Baits are also sold for the same purpose. For these products to be most effective, they should be used in wet weather in the late afternoon or evening when slugs and snails are most active. Since only moist baits attract the pests, the soil should be damp when these products are used.
Chemicals should not be used on the leaves and edible parts of garden vegetables. Make sure that children and pets can't get at the bait, which can cause poisoning.
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